[02/18] fsinfo: Add fsinfo() syscall to query filesystem information [ver #21]

Commit Message

David Howells Aug. 3, 2020, 1:36 p.m. UTC

Add a system call to allow filesystem information to be queried.  A request
value can be given to indicate the desired attribute.  Support is provided
for enumerating multi-value attributes.

===============
NEW SYSTEM CALL
===============

The new system call looks like:

	int ret = fsinfo(int dfd,
			 const char *pathname,
			 const struct fsinfo_params *params,
			 size_t params_size,
			 void *result_buffer,
			 size_t result_buf_size);

The params parameter optionally points to a block of parameters:

	struct fsinfo_params {
		__u64	resolve_flags;
		__u32	at_flags;
		__u32	flags;
		__u32	request;
		__u32	Nth;
		__u32	Mth;
	};

If params is NULL, the default is that params->request is
FSINFO_ATTR_STATFS and all the other fields are 0.  params_size indicates
the size of the parameter struct.  If the parameter block is short compared
to what the kernel expects, the missing length will be set to 0; if the
parameter block is longer, an error will be given if the excess is not all
zeros.

The object to be queried is specified as follows - part param->flags
indicates the type of reference:

 (1) FSINFO_FLAGS_QUERY_PATH - dfd, pathname and at_flags indicate a
     filesystem object to query.

     There is no separate system call providing an analogue of lstat() -
     AT_SYMLINK_NOFOLLOW should be set in at_flags instead.
     AT_NO_AUTOMOUNT can also be used to an allow automount point to be
     queried without triggering it.

     RESOLVE_* flags can also be set in resolve_flags to further restrict
     the patchwalk.

 (2) FSINFO_FLAGS_QUERY_FD - dfd indicates a file descriptor pointing to
     the filesystem object to query.  pathname should be NULL.

 (3) FSINFO_FLAGS_QUERY_MOUNT - pathname indicates the numeric ID of the
     mountpoint to query as a string.  dfd is used to constrain which
     mounts can be accessed.  If dfd is AT_FDCWD, the mount must be within
     the subtree rooted at chroot, otherwise the mount must be within the
     subtree rooted at the directory specified by dfd.

 (4) In the future FSINFO_FLAGS_QUERY_FSCONTEXT will be added - dfd will
     indicate a context handle fd obtained from fsopen() or fspick(),
     allowing that to be queried before the target superblock is attached
     to the filesystem or even created.

params->request indicates the attribute/attributes to be queried.  This can
be one of:

	FSINFO_ATTR_STATFS		- statfs-style info
	FSINFO_ATTR_IDS			- Filesystem IDs
	FSINFO_ATTR_LIMITS		- Filesystem limits
	FSINFO_ATTR_SUPPORTS		- Support for statx, ioctl, etc.
	FSINFO_ATTR_TIMESTAMP_INFO	- Inode timestamp info
	FSINFO_ATTR_VOLUME_ID		- Volume ID (string)
	FSINFO_ATTR_VOLUME_UUID		- Volume UUID
	FSINFO_ATTR_VOLUME_NAME		- Volume name (string)
	FSINFO_ATTR_FSINFO_ATTRIBUTE_INFO - Information about attr Nth
	FSINFO_ATTR_FSINFO_ATTRIBUTES	- List of supported attrs

Some attributes (such as the servers backing a network filesystem) can have
multiple values.  These can be enumerated by setting params->Nth and
params->Mth to 0, 1, ... until ENODATA is returned.

result_buffer and result_buf_size point to the reply buffer.  The buffer is
filled up to the specified size, even if this means truncating the reply.
The size of the full reply is returned, irrespective of the amount data
that was copied.  In future versions, this will allow extra fields to be
tacked on to the end of the reply, but anyone not expecting them will only
get the subset they're expecting.  If either buffer of result_buf_size are
0, no copy will take place and the data size will be returned.

Signed-off-by: David Howells <[e-mail]>
cc: [e-mail]
---

 arch/alpha/kernel/syscalls/syscall.tbl      |    1 
 arch/arm/tools/syscall.tbl                  |    1 
 arch/arm64/include/asm/unistd.h             |    2 
 arch/arm64/include/asm/unistd32.h           |    2 
 arch/ia64/kernel/syscalls/syscall.tbl       |    1 
 arch/m68k/kernel/syscalls/syscall.tbl       |    1 
 arch/microblaze/kernel/syscalls/syscall.tbl |    1 
 arch/mips/kernel/syscalls/syscall_n32.tbl   |    1 
 arch/mips/kernel/syscalls/syscall_n64.tbl   |    1 
 arch/mips/kernel/syscalls/syscall_o32.tbl   |    1 
 arch/parisc/kernel/syscalls/syscall.tbl     |    1 
 arch/powerpc/kernel/syscalls/syscall.tbl    |    1 
 arch/s390/kernel/syscalls/syscall.tbl       |    1 
 arch/sh/kernel/syscalls/syscall.tbl         |    1 
 arch/sparc/kernel/syscalls/syscall.tbl      |    1 
 arch/x86/entry/syscalls/syscall_32.tbl      |    1 
 arch/x86/entry/syscalls/syscall_64.tbl      |    1 
 arch/xtensa/kernel/syscalls/syscall.tbl     |    1 
 fs/Kconfig                                  |    7 
 fs/Makefile                                 |    1 
 fs/fsinfo.c                                 |  596 +++++++++++++++++++++++++
 include/linux/fs.h                          |    4 
 include/linux/fsinfo.h                      |   74 +++
 include/linux/syscalls.h                    |    4 
 include/uapi/asm-generic/unistd.h           |    4 
 include/uapi/linux/fsinfo.h                 |  189 ++++++++
 kernel/sys_ni.c                             |    1 
 samples/vfs/Makefile                        |    2 
 samples/vfs/test-fsinfo.c                   |  646 +++++++++++++++++++++++++++
 29 files changed, 1545 insertions(+), 3 deletions(-)
 create mode 100644 fs/fsinfo.c
 create mode 100644 include/linux/fsinfo.h
 create mode 100644 include/uapi/linux/fsinfo.h
 create mode 100644 samples/vfs/test-fsinfo.c

Comments

Miklos Szeredi Aug. 4, 2020, 10:16 a.m. UTC | #1

On Mon, Aug 03, 2020 at 02:36:42PM +0100, David Howells wrote:
> Add a system call to allow filesystem information to be queried.  A request
> value can be given to indicate the desired attribute.  Support is provided
> for enumerating multi-value attributes.
> 
> ===============
> NEW SYSTEM CALL
> ===============
> 
> The new system call looks like:
> 
> 	int ret = fsinfo(int dfd,
> 			 const char *pathname,
> 			 const struct fsinfo_params *params,
> 			 size_t params_size,
> 			 void *result_buffer,
> 			 size_t result_buf_size);
> 
> The params parameter optionally points to a block of parameters:
> 
> 	struct fsinfo_params {
> 		__u64	resolve_flags;
> 		__u32	at_flags;
> 		__u32	flags;
> 		__u32	request;
> 		__u32	Nth;
> 		__u32	Mth;

The Mth field seems to be unused in this patchset.  Since the struct is
extensible, I guess there's no point in adding it now.

> 	};
> 
> If params is NULL, the default is that params->request is
> FSINFO_ATTR_STATFS and all the other fields are 0.  params_size indicates
> the size of the parameter struct.  If the parameter block is short compared
> to what the kernel expects, the missing length will be set to 0; if the
> parameter block is longer, an error will be given if the excess is not all
> zeros.
> 
> The object to be queried is specified as follows - part param->flags
> indicates the type of reference:
> 
>  (1) FSINFO_FLAGS_QUERY_PATH - dfd, pathname and at_flags indicate a
>      filesystem object to query.
> 
>      There is no separate system call providing an analogue of lstat() -
>      AT_SYMLINK_NOFOLLOW should be set in at_flags instead.
>      AT_NO_AUTOMOUNT can also be used to an allow automount point to be
>      queried without triggering it.
> 
>      RESOLVE_* flags can also be set in resolve_flags to further restrict
>      the patchwalk.
> 
>  (2) FSINFO_FLAGS_QUERY_FD - dfd indicates a file descriptor pointing to
>      the filesystem object to query.  pathname should be NULL.

This is at_flags = AT_EMPTY_PATH by convention.


> 
>  (3) FSINFO_FLAGS_QUERY_MOUNT - pathname indicates the numeric ID of the
>      mountpoint to query as a string.  dfd is used to constrain which
>      mounts can be accessed.  If dfd is AT_FDCWD, the mount must be within
>      the subtree rooted at chroot, otherwise the mount must be within the
>      subtree rooted at the directory specified by dfd.
> 
>  (4) In the future FSINFO_FLAGS_QUERY_FSCONTEXT will be added - dfd will
>      indicate a context handle fd obtained from fsopen() or fspick(),
>      allowing that to be queried before the target superblock is attached
>      to the filesystem or even created.

Can you describe features that are added by *this* patch?  It's compex enough as
is.

> 
> params->request indicates the attribute/attributes to be queried.  This can
> be one of:
> 
> 	FSINFO_ATTR_STATFS		- statfs-style info
> 	FSINFO_ATTR_IDS			- Filesystem IDs
> 	FSINFO_ATTR_LIMITS		- Filesystem limits
> 	FSINFO_ATTR_SUPPORTS		- Support for statx, ioctl, etc.
> 	FSINFO_ATTR_TIMESTAMP_INFO	- Inode timestamp info
> 	FSINFO_ATTR_VOLUME_ID		- Volume ID (string)
> 	FSINFO_ATTR_VOLUME_UUID		- Volume UUID
> 	FSINFO_ATTR_VOLUME_NAME		- Volume name (string)
> 	FSINFO_ATTR_FSINFO_ATTRIBUTE_INFO - Information about attr Nth
> 	FSINFO_ATTR_FSINFO_ATTRIBUTES	- List of supported attrs
> 
> Some attributes (such as the servers backing a network filesystem) can have
> multiple values.  These can be enumerated by setting params->Nth and
> params->Mth to 0, 1, ... until ENODATA is returned.
> 
> result_buffer and result_buf_size point to the reply buffer.  The buffer is
> filled up to the specified size, even if this means truncating the reply.
> The size of the full reply is returned, irrespective of the amount data
> that was copied.  In future versions, this will allow extra fields to be
> tacked on to the end of the reply, but anyone not expecting them will only
> get the subset they're expecting.  If either buffer of result_buf_size are
> 0, no copy will take place and the data size will be returned.
> 
> Signed-off-by: David Howells <[e-mail]>
> cc: [e-mail]
> ---
> 
>  arch/alpha/kernel/syscalls/syscall.tbl      |    1 
>  arch/arm/tools/syscall.tbl                  |    1 
>  arch/arm64/include/asm/unistd.h             |    2 
>  arch/arm64/include/asm/unistd32.h           |    2 
>  arch/ia64/kernel/syscalls/syscall.tbl       |    1 
>  arch/m68k/kernel/syscalls/syscall.tbl       |    1 
>  arch/microblaze/kernel/syscalls/syscall.tbl |    1 
>  arch/mips/kernel/syscalls/syscall_n32.tbl   |    1 
>  arch/mips/kernel/syscalls/syscall_n64.tbl   |    1 
>  arch/mips/kernel/syscalls/syscall_o32.tbl   |    1 
>  arch/parisc/kernel/syscalls/syscall.tbl     |    1 
>  arch/powerpc/kernel/syscalls/syscall.tbl    |    1 
>  arch/s390/kernel/syscalls/syscall.tbl       |    1 
>  arch/sh/kernel/syscalls/syscall.tbl         |    1 
>  arch/sparc/kernel/syscalls/syscall.tbl      |    1 
>  arch/x86/entry/syscalls/syscall_32.tbl      |    1 
>  arch/x86/entry/syscalls/syscall_64.tbl      |    1 
>  arch/xtensa/kernel/syscalls/syscall.tbl     |    1 
>  fs/Kconfig                                  |    7 
>  fs/Makefile                                 |    1 
>  fs/fsinfo.c                                 |  596 +++++++++++++++++++++++++
>  include/linux/fs.h                          |    4 
>  include/linux/fsinfo.h                      |   74 +++
>  include/linux/syscalls.h                    |    4 
>  include/uapi/asm-generic/unistd.h           |    4 
>  include/uapi/linux/fsinfo.h                 |  189 ++++++++
>  kernel/sys_ni.c                             |    1 
>  samples/vfs/Makefile                        |    2 
>  samples/vfs/test-fsinfo.c                   |  646 +++++++++++++++++++++++++++
>  29 files changed, 1545 insertions(+), 3 deletions(-)
>  create mode 100644 fs/fsinfo.c
>  create mode 100644 include/linux/fsinfo.h
>  create mode 100644 include/uapi/linux/fsinfo.h
>  create mode 100644 samples/vfs/test-fsinfo.c
> 
> diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl
> index b6cf8403da35..984abd1ac058 100644
> --- a/arch/alpha/kernel/syscalls/syscall.tbl
> +++ b/arch/alpha/kernel/syscalls/syscall.tbl
> @@ -479,3 +479,4 @@
>  548	common	pidfd_getfd			sys_pidfd_getfd
>  549	common	faccessat2			sys_faccessat2
>  550	common	watch_mount			sys_watch_mount
> +551	common	fsinfo				sys_fsinfo
> diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl
> index 27cc1f53f4a0..bd791f91f5bb 100644
> --- a/arch/arm/tools/syscall.tbl
> +++ b/arch/arm/tools/syscall.tbl
> @@ -453,3 +453,4 @@
>  438	common	pidfd_getfd			sys_pidfd_getfd
>  439	common	faccessat2			sys_faccessat2
>  440	common	watch_mount			sys_watch_mount
> +441	common	fsinfo				sys_fsinfo
> diff --git a/arch/arm64/include/asm/unistd.h b/arch/arm64/include/asm/unistd.h
> index b3b2019f8d16..86a9d7b3eabe 100644
> --- a/arch/arm64/include/asm/unistd.h
> +++ b/arch/arm64/include/asm/unistd.h
> @@ -38,7 +38,7 @@
>  #define __ARM_NR_compat_set_tls		(__ARM_NR_COMPAT_BASE + 5)
>  #define __ARM_NR_COMPAT_END		(__ARM_NR_COMPAT_BASE + 0x800)
>  
> -#define __NR_compat_syscalls		441
> +#define __NR_compat_syscalls		442
>  #endif
>  
>  #define __ARCH_WANT_SYS_CLONE
> diff --git a/arch/arm64/include/asm/unistd32.h b/arch/arm64/include/asm/unistd32.h
> index 4f9cf98cdf0f..bd78eb2c487a 100644
> --- a/arch/arm64/include/asm/unistd32.h
> +++ b/arch/arm64/include/asm/unistd32.h
> @@ -887,6 +887,8 @@ __SYSCALL(__NR_pidfd_getfd, sys_pidfd_getfd)
>  __SYSCALL(__NR_faccessat2, sys_faccessat2)
>  #define __NR_watch_mount 440
>  __SYSCALL(__NR_watch_mount, sys_watch_mount)
> +#define __NR_fsinfo 441
> +__SYSCALL(__NR_fsinfo, sys_fsinfo)
>  
>  /*
>   * Please add new compat syscalls above this comment and update
> diff --git a/arch/ia64/kernel/syscalls/syscall.tbl b/arch/ia64/kernel/syscalls/syscall.tbl
> index fc6d87903781..09d144487b7d 100644
> --- a/arch/ia64/kernel/syscalls/syscall.tbl
> +++ b/arch/ia64/kernel/syscalls/syscall.tbl
> @@ -360,3 +360,4 @@
>  438	common	pidfd_getfd			sys_pidfd_getfd
>  439	common	faccessat2			sys_faccessat2
>  440	common	watch_mount			sys_watch_mount
> +441	common	fsinfo				sys_fsinfo
> diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl
> index c671aa0e4d25..1bdc26af3c54 100644
> --- a/arch/m68k/kernel/syscalls/syscall.tbl
> +++ b/arch/m68k/kernel/syscalls/syscall.tbl
> @@ -439,3 +439,4 @@
>  438	common	pidfd_getfd			sys_pidfd_getfd
>  439	common	faccessat2			sys_faccessat2
>  440	common	watch_mount			sys_watch_mount
> +441	common	fsinfo				sys_fsinfo
> diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl
> index 65cc53f129ef..fb8543122904 100644
> --- a/arch/microblaze/kernel/syscalls/syscall.tbl
> +++ b/arch/microblaze/kernel/syscalls/syscall.tbl
> @@ -445,3 +445,4 @@
>  438	common	pidfd_getfd			sys_pidfd_getfd
>  439	common	faccessat2			sys_faccessat2
>  440	common	watch_mount			sys_watch_mount
> +441	common	fsinfo				sys_fsinfo
> diff --git a/arch/mips/kernel/syscalls/syscall_n32.tbl b/arch/mips/kernel/syscalls/syscall_n32.tbl
> index 7f034a239930..b8362bd6bd4a 100644
> --- a/arch/mips/kernel/syscalls/syscall_n32.tbl
> +++ b/arch/mips/kernel/syscalls/syscall_n32.tbl
> @@ -378,3 +378,4 @@
>  438	n32	pidfd_getfd			sys_pidfd_getfd
>  439	n32	faccessat2			sys_faccessat2
>  440	n32	watch_mount			sys_watch_mount
> +441	n32	fsinfo				sys_fsinfo
> diff --git a/arch/mips/kernel/syscalls/syscall_n64.tbl b/arch/mips/kernel/syscalls/syscall_n64.tbl
> index d39b90de3642..60ca4091d378 100644
> --- a/arch/mips/kernel/syscalls/syscall_n64.tbl
> +++ b/arch/mips/kernel/syscalls/syscall_n64.tbl
> @@ -354,3 +354,4 @@
>  438	n64	pidfd_getfd			sys_pidfd_getfd
>  439	n64	faccessat2			sys_faccessat2
>  440	n64	watch_mount			sys_watch_mount
> +441	n64	fsinfo				sys_fsinfo
> diff --git a/arch/mips/kernel/syscalls/syscall_o32.tbl b/arch/mips/kernel/syscalls/syscall_o32.tbl
> index 09f426cb45b1..07aea9379ca0 100644
> --- a/arch/mips/kernel/syscalls/syscall_o32.tbl
> +++ b/arch/mips/kernel/syscalls/syscall_o32.tbl
> @@ -427,3 +427,4 @@
>  438	o32	pidfd_getfd			sys_pidfd_getfd
>  439	o32	faccessat2			sys_faccessat2
>  440	o32	watch_mount			sys_watch_mount
> +441	o32	fsinfo				sys_fsinfo
> diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl
> index 52ff3454baa1..f8060767f11a 100644
> --- a/arch/parisc/kernel/syscalls/syscall.tbl
> +++ b/arch/parisc/kernel/syscalls/syscall.tbl
> @@ -437,3 +437,4 @@
>  438	common	pidfd_getfd			sys_pidfd_getfd
>  439	common	faccessat2			sys_faccessat2
>  440	common	watch_mount			sys_watch_mount
> +441	common	fsinfo				sys_fsinfo
> diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl
> index 10b7ed3c7a1b..3036bf1336d2 100644
> --- a/arch/powerpc/kernel/syscalls/syscall.tbl
> +++ b/arch/powerpc/kernel/syscalls/syscall.tbl
> @@ -529,3 +529,4 @@
>  438	common	pidfd_getfd			sys_pidfd_getfd
>  439	common	faccessat2			sys_faccessat2
>  440	common	watch_mount			sys_watch_mount
> +441	common	fsinfo				sys_fsinfo
> diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl
> index 86f317bf52df..c0a111fdb3ce 100644
> --- a/arch/s390/kernel/syscalls/syscall.tbl
> +++ b/arch/s390/kernel/syscalls/syscall.tbl
> @@ -442,3 +442,4 @@
>  438  common	pidfd_getfd		sys_pidfd_getfd			sys_pidfd_getfd
>  439  common	faccessat2		sys_faccessat2			sys_faccessat2
>  440	common	watch_mount		sys_watch_mount			sys_watch_mount
> +441	common	fsinfo			sys_fsinfo			sys_fsinfo
> diff --git a/arch/sh/kernel/syscalls/syscall.tbl b/arch/sh/kernel/syscalls/syscall.tbl
> index 0bb0f0b372c7..03b55c32441f 100644
> --- a/arch/sh/kernel/syscalls/syscall.tbl
> +++ b/arch/sh/kernel/syscalls/syscall.tbl
> @@ -442,3 +442,4 @@
>  438	common	pidfd_getfd			sys_pidfd_getfd
>  439	common	faccessat2			sys_faccessat2
>  440	common	watch_mount			sys_watch_mount
> +441	common	fsinfo				sys_fsinfo
> diff --git a/arch/sparc/kernel/syscalls/syscall.tbl b/arch/sparc/kernel/syscalls/syscall.tbl
> index 369ab65c1e9a..a0144db9fb8c 100644
> --- a/arch/sparc/kernel/syscalls/syscall.tbl
> +++ b/arch/sparc/kernel/syscalls/syscall.tbl
> @@ -485,3 +485,4 @@
>  438	common	pidfd_getfd			sys_pidfd_getfd
>  439	common	faccessat2			sys_faccessat2
>  440	common	watch_mount			sys_watch_mount
> +441	common	fsinfo				sys_fsinfo
> diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
> index e760ba92c58d..edf90a2be0b9 100644
> --- a/arch/x86/entry/syscalls/syscall_32.tbl
> +++ b/arch/x86/entry/syscalls/syscall_32.tbl
> @@ -444,3 +444,4 @@
>  438	i386	pidfd_getfd		sys_pidfd_getfd
>  439	i386	faccessat2		sys_faccessat2
>  440	i386	watch_mount		sys_watch_mount
> +441	i386	fsinfo			sys_fsinfo
> diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
> index 5b58621d4f75..ab0eda639d67 100644
> --- a/arch/x86/entry/syscalls/syscall_64.tbl
> +++ b/arch/x86/entry/syscalls/syscall_64.tbl
> @@ -361,6 +361,7 @@
>  438	common	pidfd_getfd		sys_pidfd_getfd
>  439	common	faccessat2		sys_faccessat2
>  440	common	watch_mount		sys_watch_mount
> +441	common	fsinfo			sys_fsinfo
>  
>  #
>  # x32-specific system call numbers start at 512 to avoid cache impact
> diff --git a/arch/xtensa/kernel/syscalls/syscall.tbl b/arch/xtensa/kernel/syscalls/syscall.tbl
> index 5b28ee39f70f..979013890caf 100644
> --- a/arch/xtensa/kernel/syscalls/syscall.tbl
> +++ b/arch/xtensa/kernel/syscalls/syscall.tbl
> @@ -410,3 +410,4 @@
>  438	common	pidfd_getfd			sys_pidfd_getfd
>  439	common	faccessat2			sys_faccessat2
>  440	common	watch_mount			sys_watch_mount
> +441	common	fsinfo				sys_fsinfo
> diff --git a/fs/Kconfig b/fs/Kconfig
> index 1a55e56d5c54..df76451ab49a 100644
> --- a/fs/Kconfig
> +++ b/fs/Kconfig
> @@ -15,6 +15,13 @@ config VALIDATE_FS_PARSER
>  	  Enable this to perform validation of the parameter description for a
>  	  filesystem when it is registered.
>  
> +config FSINFO
> +	bool "Enable the fsinfo() system call"
> +	help
> +	  Enable the file system information querying system call to allow
> +	  comprehensive information to be retrieved about a filesystem,
> +	  superblock or mount object.
> +
>  if BLOCK
>  
>  config FS_IOMAP
> diff --git a/fs/Makefile b/fs/Makefile
> index dd0d87e2ef19..93a7f8047585 100644
> --- a/fs/Makefile
> +++ b/fs/Makefile
> @@ -55,6 +55,7 @@ obj-$(CONFIG_COREDUMP)		+= coredump.o
>  obj-$(CONFIG_SYSCTL)		+= drop_caches.o
>  
>  obj-$(CONFIG_FHANDLE)		+= fhandle.o
> +obj-$(CONFIG_FSINFO)		+= fsinfo.o
>  obj-y				+= iomap/
>  
>  obj-y				+= quota/
> diff --git a/fs/fsinfo.c b/fs/fsinfo.c
> new file mode 100644
> index 000000000000..7d9c73e9cbde
> --- /dev/null
> +++ b/fs/fsinfo.c
> @@ -0,0 +1,596 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Filesystem information query.
> + *
> + * Copyright (C) 2020 Red Hat, Inc. All Rights Reserved.
> + * Written by David Howells ([e-mail])
> + */
> +#include <linux/syscalls.h>
> +#include <linux/fs.h>
> +#include <linux/file.h>
> +#include <linux/mount.h>
> +#include <linux/namei.h>
> +#include <linux/statfs.h>
> +#include <linux/security.h>
> +#include <linux/uaccess.h>
> +#include <linux/fsinfo.h>
> +#include <uapi/linux/mount.h>
> +#include "internal.h"
> +
> +/**
> + * fsinfo_opaque - Store opaque blob as an fsinfo attribute value.
> + * @s: The blob to store (may be NULL)
> + * @ctx: The parameter context
> + * @len: The length of the blob
> + */
> +int fsinfo_opaque(const void *s, struct fsinfo_context *ctx, unsigned int len)
> +{
> +	void *p = ctx->buffer;
> +	int ret = 0;
> +
> +	if (s) {
> +		if (!ctx->want_size_only)
> +			memcpy(p, s, len);
> +		ret = len;
> +	}
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL(fsinfo_opaque);
> +
> +/**
> + * fsinfo_string - Store a NUL-terminated string as an fsinfo attribute value.
> + * @s: The string to store (may be NULL)
> + * @ctx: The parameter context
> + */
> +int fsinfo_string(const char *s, struct fsinfo_context *ctx)
> +{
> +	if (!s)
> +		return 1;
> +	return fsinfo_opaque(s, ctx, min_t(size_t, strlen(s) + 1, ctx->buf_size));
> +}
> +EXPORT_SYMBOL(fsinfo_string);
> +
> +/*
> + * Get basic filesystem stats from statfs.
> + */
> +static int fsinfo_generic_statfs(struct path *path, struct fsinfo_context *ctx)
> +{
> +	struct fsinfo_statfs *p = ctx->buffer;
> +	struct kstatfs buf;
> +	int ret;
> +
> +	ret = vfs_statfs(path, &buf);
> +	if (ret < 0)
> +		return ret;
> +
> +	p->f_blocks.lo	= buf.f_blocks;
> +	p->f_bfree.lo	= buf.f_bfree;
> +	p->f_bavail.lo	= buf.f_bavail;
> +	p->f_files.lo	= buf.f_files;
> +	p->f_ffree.lo	= buf.f_ffree;
> +	p->f_favail.lo	= buf.f_ffree;
> +	p->f_bsize	= buf.f_bsize;
> +	p->f_frsize	= buf.f_frsize;
> +	return sizeof(*p);
> +}
> +
> +static int fsinfo_generic_ids(struct path *path, struct fsinfo_context *ctx)
> +{
> +	struct fsinfo_ids *p = ctx->buffer;
> +	struct super_block *sb;
> +	struct kstatfs buf;
> +	int ret;
> +
> +	ret = vfs_statfs(path, &buf);
> +	if (ret < 0 && ret != -ENOSYS)
> +		return ret;
> +	if (ret == 0)
> +		memcpy(&p->f_fsid, &buf.f_fsid, sizeof(p->f_fsid));
> +
> +	sb = path->dentry->d_sb;
> +	p->f_fstype	= sb->s_magic;
> +	p->f_dev_major	= MAJOR(sb->s_dev);
> +	p->f_dev_minor	= MINOR(sb->s_dev);
> +	p->f_sb_id	= sb->s_unique_id;
> +	strlcpy(p->f_fs_name, sb->s_type->name, sizeof(p->f_fs_name));
> +	return sizeof(*p);
> +}
> +
> +int fsinfo_generic_limits(struct path *path, struct fsinfo_context *ctx)
> +{
> +	struct fsinfo_limits *p = ctx->buffer;
> +	struct super_block *sb = path->dentry->d_sb;
> +
> +	p->max_file_size.hi	= 0;
> +	p->max_file_size.lo	= sb->s_maxbytes;
> +	p->max_ino.hi		= 0;
> +	p->max_ino.lo		= UINT_MAX;
> +	p->max_hard_links	= sb->s_max_links;
> +	p->max_uid		= UINT_MAX;
> +	p->max_gid		= UINT_MAX;
> +	p->max_projid		= UINT_MAX;
> +	p->max_filename_len	= NAME_MAX;
> +	p->max_symlink_len	= PATH_MAX;
> +	p->max_xattr_name_len	= XATTR_NAME_MAX;
> +	p->max_xattr_body_len	= XATTR_SIZE_MAX;
> +	p->max_dev_major	= 0xffffff;
> +	p->max_dev_minor	= 0xff;
> +	return sizeof(*p);
> +}
> +EXPORT_SYMBOL(fsinfo_generic_limits);
> +
> +int fsinfo_generic_supports(struct path *path, struct fsinfo_context *ctx)
> +{
> +	struct fsinfo_supports *p = ctx->buffer;
> +	struct super_block *sb = path->dentry->d_sb;
> +
> +	p->stx_mask = STATX_BASIC_STATS;
> +	if (sb->s_d_op && sb->s_d_op->d_automount)
> +		p->stx_attributes |= STATX_ATTR_AUTOMOUNT;
> +	return sizeof(*p);
> +}
> +EXPORT_SYMBOL(fsinfo_generic_supports);
> +
> +static const struct fsinfo_timestamp_info fsinfo_default_timestamp_info = {
> +	.atime = {
> +		.minimum	= S64_MIN,
> +		.maximum	= S64_MAX,
> +		.gran_mantissa	= 1,
> +		.gran_exponent	= 0,
> +	},
> +	.mtime = {
> +		.minimum	= S64_MIN,
> +		.maximum	= S64_MAX,
> +		.gran_mantissa	= 1,
> +		.gran_exponent	= 0,
> +	},
> +	.ctime = {
> +		.minimum	= S64_MIN,
> +		.maximum	= S64_MAX,
> +		.gran_mantissa	= 1,
> +		.gran_exponent	= 0,
> +	},
> +	.btime = {
> +		.minimum	= S64_MIN,
> +		.maximum	= S64_MAX,
> +		.gran_mantissa	= 1,
> +		.gran_exponent	= 0,
> +	},
> +};
> +
> +int fsinfo_generic_timestamp_info(struct path *path, struct fsinfo_context *ctx)
> +{
> +	struct fsinfo_timestamp_info *p = ctx->buffer;
> +	struct super_block *sb = path->dentry->d_sb;
> +	s8 exponent;
> +
> +	*p = fsinfo_default_timestamp_info;
> +
> +	if (sb->s_time_gran < 1000000000) {
> +		if (sb->s_time_gran < 1000)
> +			exponent = -9;
> +		else if (sb->s_time_gran < 1000000)
> +			exponent = -6;
> +		else
> +			exponent = -3;
> +
> +		p->atime.gran_exponent = exponent;
> +		p->mtime.gran_exponent = exponent;
> +		p->ctime.gran_exponent = exponent;
> +		p->btime.gran_exponent = exponent;
> +	}
> +
> +	return sizeof(*p);
> +}
> +EXPORT_SYMBOL(fsinfo_generic_timestamp_info);
> +
> +static int fsinfo_generic_volume_uuid(struct path *path, struct fsinfo_context *ctx)
> +{
> +	struct fsinfo_volume_uuid *p = ctx->buffer;
> +	struct super_block *sb = path->dentry->d_sb;
> +
> +	memcpy(p, &sb->s_uuid, sizeof(*p));
> +	return sizeof(*p);
> +}
> +
> +static int fsinfo_generic_volume_id(struct path *path, struct fsinfo_context *ctx)
> +{
> +	return fsinfo_string(path->dentry->d_sb->s_id, ctx);
> +}
> +
> +static const struct fsinfo_attribute fsinfo_common_attributes[] = {
> +	FSINFO_VSTRUCT	(FSINFO_ATTR_STATFS,		fsinfo_generic_statfs),
> +	FSINFO_VSTRUCT	(FSINFO_ATTR_IDS,		fsinfo_generic_ids),
> +	FSINFO_VSTRUCT	(FSINFO_ATTR_LIMITS,		fsinfo_generic_limits),
> +	FSINFO_VSTRUCT	(FSINFO_ATTR_SUPPORTS,		fsinfo_generic_supports),
> +	FSINFO_VSTRUCT	(FSINFO_ATTR_TIMESTAMP_INFO,	fsinfo_generic_timestamp_info),
> +	FSINFO_STRING	(FSINFO_ATTR_VOLUME_ID,		fsinfo_generic_volume_id),
> +	FSINFO_VSTRUCT	(FSINFO_ATTR_VOLUME_UUID,	fsinfo_generic_volume_uuid),
> +
> +	FSINFO_LIST	(FSINFO_ATTR_FSINFO_ATTRIBUTES,	(void *)123UL),
> +	FSINFO_VSTRUCT_N(FSINFO_ATTR_FSINFO_ATTRIBUTE_INFO, (void *)123UL),
> +	{}
> +};
> +
> +/*
> + * Determine an attribute's minimum buffer size and, if the buffer is large
> + * enough, get the attribute value.
> + */
> +static int fsinfo_get_this_attribute(struct path *path,
> +				     struct fsinfo_context *ctx,
> +				     const struct fsinfo_attribute *attr)
> +{
> +	int buf_size;
> +
> +	if (ctx->Nth != 0 && !(attr->flags & (FSINFO_FLAGS_N | FSINFO_FLAGS_NM)))
> +		return -ENODATA;
> +	if (ctx->Mth != 0 && !(attr->flags & FSINFO_FLAGS_NM))
> +		return -ENODATA;
> +
> +	switch (attr->type) {
> +	case FSINFO_TYPE_VSTRUCT:
> +		ctx->clear_tail = true;
> +		buf_size = attr->size;
> +		break;
> +	case FSINFO_TYPE_STRING:
> +	case FSINFO_TYPE_OPAQUE:
> +	case FSINFO_TYPE_LIST:
> +		buf_size = 4096;
> +		break;
> +	default:
> +		return -ENOPKG;
> +	}
> +
> +	if (ctx->buf_size < buf_size)
> +		return buf_size;
> +
> +	return attr->get(path, ctx);
> +}
> +
> +static void fsinfo_attributes_insert(struct fsinfo_context *ctx,
> +				     const struct fsinfo_attribute *attr)
> +{
> +	__u32 *p = ctx->buffer;
> +	unsigned int i;
> +
> +	if (ctx->usage >= ctx->buf_size ||
> +	    ctx->buf_size - ctx->usage < sizeof(__u32)) {
> +		ctx->usage += sizeof(__u32);
> +		return;
> +	}
> +
> +	for (i = 0; i < ctx->usage / sizeof(__u32); i++)
> +		if (p[i] == attr->attr_id)
> +			return;
> +
> +	p[i] = attr->attr_id;
> +	ctx->usage += sizeof(__u32);
> +}
> +
> +static int fsinfo_list_attributes(struct path *path,
> +				  struct fsinfo_context *ctx,
> +				  const struct fsinfo_attribute *attributes)
> +{
> +	const struct fsinfo_attribute *a;
> +
> +	for (a = attributes; a->get; a++)
> +		fsinfo_attributes_insert(ctx, a);
> +	return -EOPNOTSUPP; /* We want to go through all the lists */
> +}
> +
> +static int fsinfo_get_attribute_info(struct path *path,
> +				     struct fsinfo_context *ctx,
> +				     const struct fsinfo_attribute *attributes)
> +{
> +	const struct fsinfo_attribute *a;
> +	struct fsinfo_attribute_info *p = ctx->buffer;
> +
> +	if (!ctx->buf_size)
> +		return sizeof(*p);
> +
> +	for (a = attributes; a->get; a++) {
> +		if (a->attr_id == ctx->Nth) {
> +			p->attr_id	= a->attr_id;
> +			p->type		= a->type;
> +			p->flags	= a->flags;
> +			p->size		= a->size;
> +			p->size		= a->size;
> +			return sizeof(*p);
> +		}
> +	}
> +	return -EOPNOTSUPP; /* We want to go through all the lists */
> +}
> +
> +/**
> + * fsinfo_get_attribute - Look up and handle an attribute
> + * @path: The object to query
> + * @params: Parameters to define a request and place to store result
> + * @attributes: List of attributes to search.
> + *
> + * Look through a list of attributes for one that matches the requested
> + * attribute then call the handler for it.
> + */
> +int fsinfo_get_attribute(struct path *path, struct fsinfo_context *ctx,
> +			 const struct fsinfo_attribute *attributes)
> +{
> +	const struct fsinfo_attribute *a;
> +
> +	switch (ctx->requested_attr) {
> +	case FSINFO_ATTR_FSINFO_ATTRIBUTE_INFO:
> +		return fsinfo_get_attribute_info(path, ctx, attributes);
> +	case FSINFO_ATTR_FSINFO_ATTRIBUTES:
> +		return fsinfo_list_attributes(path, ctx, attributes);
> +	default:
> +		for (a = attributes; a->get; a++)
> +			if (a->attr_id == ctx->requested_attr)
> +				return fsinfo_get_this_attribute(path, ctx, a);
> +		return -EOPNOTSUPP;
> +	}
> +}
> +EXPORT_SYMBOL(fsinfo_get_attribute);
> +
> +/**
> + * generic_fsinfo - Handle an fsinfo attribute generically
> + * @path: The object to query
> + * @params: Parameters to define a request and place to store result
> + */
> +static int fsinfo_call(struct path *path, struct fsinfo_context *ctx)
> +{
> +	int ret;
> +
> +	if (path->dentry->d_sb->s_op->fsinfo) {
> +		ret = path->dentry->d_sb->s_op->fsinfo(path, ctx);
> +		if (ret != -EOPNOTSUPP)
> +			return ret;
> +	}
> +	ret = fsinfo_get_attribute(path, ctx, fsinfo_common_attributes);
> +	if (ret != -EOPNOTSUPP)
> +		return ret;
> +
> +	switch (ctx->requested_attr) {
> +	case FSINFO_ATTR_FSINFO_ATTRIBUTE_INFO:
> +		return -ENODATA;
> +	case FSINFO_ATTR_FSINFO_ATTRIBUTES:
> +		return ctx->usage;
> +	default:
> +		return -EOPNOTSUPP;
> +	}
> +}
> +
> +/**
> + * vfs_fsinfo - Retrieve filesystem information
> + * @path: The object to query
> + * @params: Parameters to define a request and place to store result
> + *
> + * Get an attribute on a filesystem or an object within a filesystem.  The
> + * filesystem attribute to be queried is indicated by @ctx->requested_attr, and
> + * if it's a multi-valued attribute, the particular value is selected by
> + * @ctx->Nth and then @ctx->Mth.
> + *
> + * For common attributes, a value may be fabricated if it is not supported by
> + * the filesystem.
> + *
> + * On success, the size of the attribute's value is returned (0 is a valid
> + * size).  A buffer will have been allocated and will be pointed to by
> + * @ctx->buffer.  The caller must free this with kvfree().
> + *
> + * Errors can also be returned: -ENOMEM if a buffer cannot be allocated, -EPERM
> + * or -EACCES if permission is denied by the LSM, -EOPNOTSUPP if an attribute
> + * doesn't exist for the specified object or -ENODATA if the attribute exists,
> + * but the Nth,Mth value does not exist.  -EMSGSIZE indicates that the value is
> + * unmanageable internally and -ENOPKG indicates other internal failure.
> + *
> + * Errors such as -EIO may also come from attempts to access media or servers
> + * to obtain the requested information if it's not immediately to hand.
> + *
> + * [*] Note that the caller may set @ctx->want_size_only if it only wants the
> + *     size of the value and not the data.  If this is set, a buffer may not be
> + *     allocated under some circumstances.  This is intended for size query by
> + *     userspace.
> + *
> + * [*] Note that @ctx->clear_tail will be returned set if the data should be
> + *     padded out with zeros when writing it to userspace.
> + */
> +static int vfs_fsinfo(struct path *path, struct fsinfo_context *ctx)
> +{
> +	struct dentry *dentry = path->dentry;
> +	int ret;
> +
> +	ret = security_sb_statfs(dentry);
> +	if (ret)
> +		return ret;
> +
> +	/* Call the handler to find out the buffer size required. */
> +	ctx->buf_size = 0;
> +	ret = fsinfo_call(path, ctx);
> +	if (ret < 0 || ctx->want_size_only)
> +		return ret;
> +	ctx->buf_size = ret;
> +
> +	do {
> +		/* Allocate a buffer of the requested size. */
> +		if (ctx->buf_size > INT_MAX)
> +			return -EMSGSIZE;
> +		ctx->buffer = kvzalloc(ctx->buf_size, GFP_KERNEL);
> +		if (!ctx->buffer)
> +			return -ENOMEM;
> +
> +		ctx->usage = 0;
> +		ctx->skip = 0;
> +		ret = fsinfo_call(path, ctx);
> +		if (IS_ERR_VALUE((long)ret))
> +			return ret;
> +		if ((unsigned int)ret <= ctx->buf_size)
> +			return ret; /* It fitted */
> +
> +		/* We need to resize the buffer */
> +		ctx->buf_size = roundup(ret, PAGE_SIZE);
> +		kvfree(ctx->buffer);
> +		ctx->buffer = NULL;
> +	} while (!signal_pending(current));
> +
> +	return -ERESTARTSYS;
> +}
> +
> +static int vfs_fsinfo_path(int dfd, const char __user *pathname,
> +			   const struct fsinfo_params *up,
> +			   struct fsinfo_context *ctx)
> +{
> +	struct path path;
> +	unsigned lookup_flags = LOOKUP_FOLLOW | LOOKUP_AUTOMOUNT;
> +	int ret = -EINVAL;
> +
> +	if (up->resolve_flags & ~VALID_RESOLVE_FLAGS)
> +		return -EINVAL;
> +	if (up->at_flags & ~(AT_SYMLINK_NOFOLLOW | AT_NO_AUTOMOUNT |
> +			     AT_EMPTY_PATH))
> +		return -EINVAL;
> +
> +	if (up->resolve_flags & RESOLVE_NO_XDEV)
> +		lookup_flags |= LOOKUP_NO_XDEV;
> +	if (up->resolve_flags & RESOLVE_NO_MAGICLINKS)
> +		lookup_flags |= LOOKUP_NO_MAGICLINKS;
> +	if (up->resolve_flags & RESOLVE_NO_SYMLINKS)
> +		lookup_flags |= LOOKUP_NO_SYMLINKS;
> +	if (up->resolve_flags & RESOLVE_BENEATH)
> +		lookup_flags |= LOOKUP_BENEATH;
> +	if (up->resolve_flags & RESOLVE_IN_ROOT)
> +		lookup_flags |= LOOKUP_IN_ROOT;
> +	if (up->at_flags & AT_SYMLINK_NOFOLLOW)
> +		lookup_flags &= ~LOOKUP_FOLLOW;
> +	if (up->at_flags & AT_NO_AUTOMOUNT)
> +		lookup_flags &= ~LOOKUP_AUTOMOUNT;
> +	if (up->at_flags & AT_EMPTY_PATH)
> +		lookup_flags |= LOOKUP_EMPTY;
> +
> +retry:
> +	ret = user_path_at(dfd, pathname, lookup_flags, &path);
> +	if (ret)
> +		goto out;
> +
> +	ret = vfs_fsinfo(&path, ctx);
> +	path_put(&path);
> +	if (retry_estale(ret, lookup_flags)) {
> +		lookup_flags |= LOOKUP_REVAL;
> +		goto retry;
> +	}
> +out:
> +	return ret;
> +}
> +
> +static int vfs_fsinfo_fd(unsigned int fd, struct fsinfo_context *ctx)
> +{
> +	struct fd f = fdget_raw(fd);
> +	int ret = -EBADF;
> +
> +	if (f.file) {
> +		ret = vfs_fsinfo(&f.file->f_path, ctx);
> +		fdput(f);
> +	}
> +	return ret;
> +}
> +
> +/**
> + * sys_fsinfo - System call to get filesystem information
> + * @dfd: Base directory to pathwalk from or fd referring to filesystem.
> + * @pathname: Filesystem to query or NULL.
> + * @params: Parameters to define request (NULL: FSINFO_ATTR_STATFS).
> + * @params_size: Size of parameter buffer.
> + * @result_buffer: Result buffer.
> + * @result_buf_size: Size of result buffer.
> + *
> + * Get information on a filesystem.  The filesystem attribute to be queried is
> + * indicated by @_params->request, and some of the attributes can have multiple
> + * values, indexed by @_params->Nth and @_params->Mth.  If @_params is NULL,
> + * then the 0th fsinfo_attr_statfs attribute is queried.  If an attribute does
> + * not exist, EOPNOTSUPP is returned; if the Nth,Mth value does not exist,
> + * ENODATA is returned.
> + *
> + * On success, the size of the attribute's value is returned.  If
> + * @result_buf_size is 0 or @result_buffer is NULL, only the size is returned.
> + * If the size of the value is larger than @result_buf_size, it will be
> + * truncated by the copy.  If the size of the value is smaller than
> + * @result_buf_size then the excess buffer space will be cleared.  The full
> + * size of the value will be returned, irrespective of how much data is
> + * actually placed in the buffer.
> + */
> +SYSCALL_DEFINE6(fsinfo,
> +		int, dfd,
> +		const char __user *, pathname,
> +		const struct fsinfo_params __user *, params,
> +		size_t, params_size,
> +		void __user *, result_buffer,
> +		size_t, result_buf_size)
> +{
> +	struct fsinfo_context ctx;
> +	struct fsinfo_params user_params;
> +	unsigned int result_size;
> +	void *r;
> +	int ret;
> +
> +	if ((!params &&  params_size) ||
> +	    ( params && !params_size) ||
> +	    (!result_buffer &&  result_buf_size) ||
> +	    ( result_buffer && !result_buf_size))
> +		return -EINVAL;
> +	if (result_buf_size > UINT_MAX)
> +		return -EOVERFLOW;
> +
> +	memset(&ctx, 0, sizeof(ctx));
> +	ctx.requested_attr	= FSINFO_ATTR_STATFS;
> +	ctx.flags		= FSINFO_FLAGS_QUERY_PATH;
> +	ctx.want_size_only	= (result_buf_size == 0);
> +
> +	if (params) {
> +		ret = copy_struct_from_user(&user_params, sizeof(user_params),
> +					    params, params_size);
> +		if (ret < 0)
> +			return ret;
> +		if (user_params.flags & ~FSINFO_FLAGS_QUERY_MASK)
> +			return -EINVAL;
> +		ctx.flags = user_params.flags;
> +		ctx.requested_attr = user_params.request;
> +		ctx.Nth = user_params.Nth;
> +		ctx.Mth = user_params.Mth;
> +	}
> +
> +	switch (ctx.flags & FSINFO_FLAGS_QUERY_MASK) {
> +	case FSINFO_FLAGS_QUERY_PATH:
> +		ret = vfs_fsinfo_path(dfd, pathname, &user_params, &ctx);
> +		break;
> +	case FSINFO_FLAGS_QUERY_FD:
> +		if (pathname)
> +			return -EINVAL;
> +		ret = vfs_fsinfo_fd(dfd, &ctx);
> +		break;
> +	default:
> +		return -EINVAL;
> +	}
> +
> +	if (ret < 0)
> +		goto error;
> +
> +	r = ctx.buffer + ctx.skip;
> +	result_size = min_t(size_t, ret, result_buf_size);
> +	if (result_size > 0 &&
> +	    copy_to_user(result_buffer, r, result_size) != 0) {
> +		ret = -EFAULT;
> +		goto error;
> +	}
> +
> +	/* Clear any part of the buffer that we won't fill if we're putting a
> +	 * struct in there.  Strings, opaque objects and arrays are expected to
> +	 * be variable length.
> +	 */
> +	if (ctx.clear_tail &&
> +	    result_buf_size > result_size &&
> +	    clear_user(result_buffer + result_size,
> +		       result_buf_size - result_size) != 0) {
> +		ret = -EFAULT;
> +		goto error;
> +	}
> +
> +error:
> +	kvfree(ctx.buffer);
> +	return ret;
> +}
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 28a29356eace..3284f497de0a 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -68,6 +68,7 @@ struct fsverity_info;
>  struct fsverity_operations;
>  struct fs_context;
>  struct fs_parameter_spec;
> +struct fsinfo_context;
>  
>  extern void __init inode_init(void);
>  extern void __init inode_init_early(void);
> @@ -1963,6 +1964,9 @@ struct super_operations {
>  	int (*thaw_super) (struct super_block *);
>  	int (*unfreeze_fs) (struct super_block *);
>  	int (*statfs) (struct dentry *, struct kstatfs *);
> +#ifdef CONFIG_FSINFO
> +	int (*fsinfo)(struct path *, struct fsinfo_context *);
> +#endif
>  	int (*remount_fs) (struct super_block *, int *, char *);
>  	void (*umount_begin) (struct super_block *);
>  
> diff --git a/include/linux/fsinfo.h b/include/linux/fsinfo.h
> new file mode 100644
> index 000000000000..a811d69b02ff
> --- /dev/null
> +++ b/include/linux/fsinfo.h
> @@ -0,0 +1,74 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Filesystem information query
> + *
> + * Copyright (C) 2020 Red Hat, Inc. All Rights Reserved.
> + * Written by David Howells ([e-mail])
> + */
> +
> +#ifndef _LINUX_FSINFO_H
> +#define _LINUX_FSINFO_H
> +
> +#ifdef CONFIG_FSINFO
> +
> +#include <uapi/linux/fsinfo.h>
> +
> +struct path;
> +
> +#define FSINFO_NORMAL_ATTR_MAX_SIZE 4096
> +
> +struct fsinfo_context {
> +	__u32		flags;		/* [in] FSINFO_FLAGS_* */
> +	__u32		requested_attr;	/* [in] What is being asking for */
> +	__u32		Nth;		/* [in] Instance of it (some may have multiple) */
> +	__u32		Mth;		/* [in] Subinstance */
> +	bool		want_size_only;	/* [in] Just want to know the size, not the data */
> +	bool		clear_tail;	/* [out] T if tail of buffer should be cleared */
> +	unsigned int	skip;		/* [out] Number of bytes to skip in buffer */
> +	unsigned int	usage;		/* [tmp] Amount of buffer used (if large) */
> +	unsigned int	buf_size;	/* [tmp] Size of ->buffer[] */
> +	void		*buffer;	/* [out] The reply buffer */
> +};
> +
> +/*
> + * A filesystem information attribute definition.
> + */
> +struct fsinfo_attribute {
> +	unsigned int		attr_id;	/* The ID of the attribute */
> +	enum fsinfo_value_type	type:8;		/* The type of the attribute's value(s) */
> +	unsigned int		flags:8;
> +	unsigned int		size:16;	/* - Value size (FSINFO_STRUCT/LIST) */
> +	int (*get)(struct path *path, struct fsinfo_context *params);
> +};
> +
> +#define __FSINFO(A, T, S, G, F) \
> +	{ .attr_id = A, .type = T, .flags = F, .size = S, .get = G }
> +
> +#define _FSINFO(A, T, S, G)	__FSINFO(A, T, S, G, 0)
> +#define _FSINFO_N(A, T, S, G)	__FSINFO(A, T, S, G, FSINFO_FLAGS_N)
> +#define _FSINFO_NM(A, T, S, G)	__FSINFO(A, T, S, G, FSINFO_FLAGS_NM)
> +
> +#define _FSINFO_VSTRUCT(A,S,G)	  _FSINFO   (A, FSINFO_TYPE_VSTRUCT, sizeof(S), G)
> +#define _FSINFO_VSTRUCT_N(A,S,G)  _FSINFO_N (A, FSINFO_TYPE_VSTRUCT, sizeof(S), G)
> +#define _FSINFO_VSTRUCT_NM(A,S,G) _FSINFO_NM(A, FSINFO_TYPE_VSTRUCT, sizeof(S), G)
> +
> +#define FSINFO_VSTRUCT(A,G)	_FSINFO_VSTRUCT   (A, A##__STRUCT, G)
> +#define FSINFO_VSTRUCT_N(A,G)	_FSINFO_VSTRUCT_N (A, A##__STRUCT, G)
> +#define FSINFO_VSTRUCT_NM(A,G)	_FSINFO_VSTRUCT_NM(A, A##__STRUCT, G)
> +#define FSINFO_STRING(A,G)	_FSINFO   (A, FSINFO_TYPE_STRING, 0, G)
> +#define FSINFO_STRING_N(A,G)	_FSINFO_N (A, FSINFO_TYPE_STRING, 0, G)
> +#define FSINFO_STRING_NM(A,G)	_FSINFO_NM(A, FSINFO_TYPE_STRING, 0, G)
> +#define FSINFO_OPAQUE(A,G)	_FSINFO   (A, FSINFO_TYPE_OPAQUE, 0, G)


The opaque type seems to be unused in this patchset.  It's definitely not
somehting we want without a good reason, so if that reason arrises, then let's
please discuss then.

> +#define FSINFO_LIST(A,G)	_FSINFO   (A, FSINFO_TYPE_LIST, sizeof(A##__STRUCT), G)
> +#define FSINFO_LIST_N(A,G)	_FSINFO_N (A, FSINFO_TYPE_LIST, sizeof(A##__STRUCT), G)
> +
> +extern int fsinfo_opaque(const void *, struct fsinfo_context *, unsigned int);
> +extern int fsinfo_string(const char *, struct fsinfo_context *);
> +extern int fsinfo_generic_timestamp_info(struct path *, struct fsinfo_context *);
> +extern int fsinfo_generic_supports(struct path *, struct fsinfo_context *);
> +extern int fsinfo_generic_limits(struct path *, struct fsinfo_context *);
> +extern int fsinfo_get_attribute(struct path *, struct fsinfo_context *,
> +				const struct fsinfo_attribute *);
> +
> +#endif /* CONFIG_FSINFO */
> +
> +#endif /* _LINUX_FSINFO_H */
> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index 88d03fd627ab..e31ad49af4c3 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -47,6 +47,7 @@ struct stat64;
>  struct statfs;
>  struct statfs64;
>  struct statx;
> +struct fsinfo_params;
>  struct __sysctl_args;
>  struct sysinfo;
>  struct timespec;
> @@ -1007,6 +1008,9 @@ asmlinkage long sys_pidfd_send_signal(int pidfd, int sig,
>  asmlinkage long sys_pidfd_getfd(int pidfd, int fd, unsigned int flags);
>  asmlinkage long sys_watch_mount(int dfd, const char __user *path,
>  				unsigned int at_flags, int watch_fd, int watch_id);
> +asmlinkage long sys_fsinfo(int dfd, const char __user *pathname,
> +			   const struct fsinfo_params __user *params, size_t params_size,
> +			   void __user *result_buffer, size_t result_buf_size);
>  
>  /*
>   * Architecture-specific system calls
> diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
> index fcdca8c7d30a..9e38f611ab56 100644
> --- a/include/uapi/asm-generic/unistd.h
> +++ b/include/uapi/asm-generic/unistd.h
> @@ -859,9 +859,11 @@ __SYSCALL(__NR_pidfd_getfd, sys_pidfd_getfd)
>  __SYSCALL(__NR_faccessat2, sys_faccessat2)
>  #define __NR_watch_mount 440
>  __SYSCALL(__NR_watch_mount, sys_watch_mount)
> +#define __NR_fsinfo 441
> +__SYSCALL(__NR_fsinfo, sys_fsinfo)
>  
>  #undef __NR_syscalls
> -#define __NR_syscalls 441
> +#define __NR_syscalls 442
>  
>  /*
>   * 32 bit systems traditionally used different
> diff --git a/include/uapi/linux/fsinfo.h b/include/uapi/linux/fsinfo.h
> new file mode 100644
> index 000000000000..65892239ba86
> --- /dev/null
> +++ b/include/uapi/linux/fsinfo.h
> @@ -0,0 +1,189 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> +/* fsinfo() definitions.
> + *
> + * Copyright (C) 2020 Red Hat, Inc. All Rights Reserved.
> + * Written by David Howells ([e-mail])
> + */
> +#ifndef _UAPI_LINUX_FSINFO_H
> +#define _UAPI_LINUX_FSINFO_H
> +
> +#include <linux/types.h>
> +#include <linux/socket.h>
> +#include <linux/openat2.h>
> +
> +/*
> + * The filesystem attributes that can be requested.  Note that some attributes
> + * may have multiple instances which can be switched in the parameter block.
> + */
> +#define FSINFO_ATTR_STATFS		0x00	/* statfs()-style state */
> +#define FSINFO_ATTR_IDS			0x01	/* Filesystem IDs */
> +#define FSINFO_ATTR_LIMITS		0x02	/* Filesystem limits */
> +#define FSINFO_ATTR_SUPPORTS		0x03	/* What's supported in statx, iocflags, ... */
> +#define FSINFO_ATTR_TIMESTAMP_INFO	0x04	/* Inode timestamp info */
> +#define FSINFO_ATTR_VOLUME_ID		0x05	/* Volume ID (string) */
> +#define FSINFO_ATTR_VOLUME_UUID		0x06	/* Volume UUID (LE uuid) */
> +#define FSINFO_ATTR_VOLUME_NAME		0x07	/* Volume name (string) */
> +
> +#define FSINFO_ATTR_FSINFO_ATTRIBUTE_INFO 0x100	/* Information about attr N (for path) */
> +#define FSINFO_ATTR_FSINFO_ATTRIBUTES	0x101	/* List of supported attrs (for path) */


I think it would make sense to move the actual attributes to a separate patch
and leave this just being the infrastructure.

> +
> +/*
> + * Optional fsinfo() parameter structure.
> + *
> + * If this is not given, it is assumed that fsinfo_attr_statfs instance 0,0 is
> + * desired.
> + */
> +struct fsinfo_params {
> +	__u64	resolve_flags;	/* RESOLVE_* flags */
> +	__u32	at_flags;	/* AT_* flags */
> +	__u32	flags;		/* Flags controlling fsinfo() specifically */
> +#define FSINFO_FLAGS_QUERY_MASK	0x0007 /* What object should fsinfo() query? */
> +#define FSINFO_FLAGS_QUERY_PATH	0x0000 /* - path, specified by dirfd,pathname,AT_EMPTY_PATH */
> +#define FSINFO_FLAGS_QUERY_FD	0x0001 /* - fd specified by dirfd */
> +	__u32	request;	/* ID of requested attribute */
> +	__u32	Nth;		/* Instance of it (some may have multiple) */
> +	__u32	Mth;		/* Subinstance of Nth instance */
> +};
> +
> +enum fsinfo_value_type {
> +	FSINFO_TYPE_VSTRUCT	= 0,	/* Version-lengthed struct (up to 4096 bytes) */
> +	FSINFO_TYPE_STRING	= 1,	/* NUL-term var-length string (up to 4095 chars) */
> +	FSINFO_TYPE_OPAQUE	= 2,	/* Opaque blob (unlimited size) */
> +	FSINFO_TYPE_LIST	= 3,	/* List of ints/structs (unlimited size) */
> +};
> +
> +/*
> + * Information struct for fsinfo(FSINFO_ATTR_FSINFO_ATTRIBUTE_INFO).
> + *
> + * This gives information about the attributes supported by fsinfo for the
> + * given path.
> + */
> +struct fsinfo_attribute_info {
> +	unsigned int		attr_id;	/* The ID of the attribute */
> +	enum fsinfo_value_type	type;		/* The type of the attribute's value(s) */
> +	unsigned int		flags;
> +#define FSINFO_FLAGS_N		0x01		/* - Attr has a set of values */
> +#define FSINFO_FLAGS_NM		0x02		/* - Attr has a set of sets of values */
> +	unsigned int		size;		/* - Value size (FSINFO_STRUCT/FSINFO_LIST) */
> +};
> +
> +#define FSINFO_ATTR_FSINFO_ATTRIBUTE_INFO__STRUCT struct fsinfo_attribute_info
> +#define FSINFO_ATTR_FSINFO_ATTRIBUTES__STRUCT __u32
> +
> +struct fsinfo_u128 {
> +#if defined(__BYTE_ORDER) ? __BYTE_ORDER == __BIG_ENDIAN : defined(__BIG_ENDIAN)
> +	__u64	hi;
> +	__u64	lo;
> +#elif defined(__BYTE_ORDER) ? __BYTE_ORDER == __LITTLE_ENDIAN : defined(__LITTLE_ENDIAN)
> +	__u64	lo;
> +	__u64	hi;
> +#endif

Shouldn't this belong in <linux/types.h>?

> +};
> +
> +/*
> + * Information struct for fsinfo(FSINFO_ATTR_STATFS).
> + * - This gives extended filesystem information.
> + */
> +struct fsinfo_statfs {
> +	struct fsinfo_u128 f_blocks;	/* Total number of blocks in fs */
> +	struct fsinfo_u128 f_bfree;	/* Total number of free blocks */
> +	struct fsinfo_u128 f_bavail;	/* Number of free blocks available to ordinary user */
> +	struct fsinfo_u128 f_files;	/* Total number of file nodes in fs */
> +	struct fsinfo_u128 f_ffree;	/* Number of free file nodes */
> +	struct fsinfo_u128 f_favail;	/* Number of file nodes available to ordinary user */


Is there a reason these are 128 wide fields?  Are we approaching the limits of
64bits?

> +	__u64	f_bsize;		/* Optimal block size */
> +	__u64	f_frsize;		/* Fragment size */
> +};
> +
> +#define FSINFO_ATTR_STATFS__STRUCT struct fsinfo_statfs
> +
> +/*
> + * Information struct for fsinfo(FSINFO_ATTR_IDS).
> + *
> + * List of basic identifiers as is normally found in statfs().
> + */
> +struct fsinfo_ids {
> +	char	f_fs_name[15 + 1];	/* Filesystem name */
> +	__u64	f_fsid;			/* Short 64-bit Filesystem ID (as statfs) */
> +	__u64	f_sb_id;		/* Internal superblock ID for sbnotify()/mntnotify() */
> +	__u32	f_fstype;		/* Filesystem type from linux/magic.h [uncond] */
> +	__u32	f_dev_major;		/* As st_dev_* from struct statx [uncond] */
> +	__u32	f_dev_minor;
> +	__u32	__padding[1];
> +};
> +
> +#define FSINFO_ATTR_IDS__STRUCT struct fsinfo_ids
> +
> +/*
> + * Information struct for fsinfo(FSINFO_ATTR_LIMITS).
> + *
> + * List of supported filesystem limits.
> + */
> +struct fsinfo_limits {
> +	struct fsinfo_u128 max_file_size;	/* Maximum file size */
> +	struct fsinfo_u128 max_ino;		/* Maximum inode number */

Again, what's the reason.  AFACT we are not yet worried about overflowing 64
bits.  Future proofing is good, but there has to be some rules and reasons
behind the decisions.

BTW, having all-string attributes (which I have advocated in the past) would
avoid having to worry about field widths.

> +	__u64	max_uid;			/* Maximum UID supported */
> +	__u64	max_gid;			/* Maximum GID supported */
> +	__u64	max_projid;			/* Maximum project ID supported */
> +	__u64	max_hard_links;			/* Maximum number of hard links on a file */
> +	__u64	max_xattr_body_len;		/* Maximum xattr content length */
> +	__u32	max_xattr_name_len;		/* Maximum xattr name length */
> +	__u32	max_filename_len;		/* Maximum filename length */
> +	__u32	max_symlink_len;		/* Maximum symlink content length */
> +	__u32	max_dev_major;			/* Maximum device major representable */
> +	__u32	max_dev_minor;			/* Maximum device minor representable */
> +	__u32	__padding[1];
> +};
> +
> +#define FSINFO_ATTR_LIMITS__STRUCT struct fsinfo_limits
> +
> +/*
> + * Information struct for fsinfo(FSINFO_ATTR_SUPPORTS).
> + *
> + * What's supported in various masks, such as statx() attribute and mask bits
> + * and IOC flags.
> + */
> +struct fsinfo_supports {
> +	__u64	stx_attributes;		/* What statx::stx_attributes are supported */
> +	__u32	stx_mask;		/* What statx::stx_mask bits are supported */
> +	__u32	fs_ioc_getflags;	/* What FS_IOC_GETFLAGS may return */
> +	__u32	fs_ioc_setflags_set;	/* What FS_IOC_SETFLAGS may set */
> +	__u32	fs_ioc_setflags_clear;	/* What FS_IOC_SETFLAGS may clear */
> +	__u32	fs_ioc_fsgetxattr_xflags; /* What FS_IOC_FSGETXATTR[A] may return in fsx_xflags */
> +	__u32	fs_ioc_fssetxattr_xflags_set; /* What FS_IOC_FSSETXATTR may set in fsx_xflags */
> +	__u32	fs_ioc_fssetxattr_xflags_clear; /* What FS_IOC_FSSETXATTR may set in fsx_xflags */
> +	__u32	win_file_attrs;		/* What DOS/Windows FILE_* attributes are supported */
> +};
> +
> +#define FSINFO_ATTR_SUPPORTS__STRUCT struct fsinfo_supports
> +
> +struct fsinfo_timestamp_one {
> +	__s64	minimum;	/* Minimum timestamp value in seconds */
> +	__s64	maximum;	/* Maximum timestamp value in seconds */
> +	__u16	gran_mantissa;	/* Granularity(secs) = mant * 10^exp */
> +	__s8	gran_exponent;
> +	__u8	__padding[5];
> +};
> +
> +/*
> + * Information struct for fsinfo(FSINFO_ATTR_TIMESTAMP_INFO).
> + */
> +struct fsinfo_timestamp_info {
> +	struct fsinfo_timestamp_one	atime;	/* Access time */
> +	struct fsinfo_timestamp_one	mtime;	/* Modification time */
> +	struct fsinfo_timestamp_one	ctime;	/* Change time */
> +	struct fsinfo_timestamp_one	btime;	/* Birth/creation time */
> +};
> +
> +#define FSINFO_ATTR_TIMESTAMP_INFO__STRUCT struct fsinfo_timestamp_info
> +
> +/*
> + * Information struct for fsinfo(FSINFO_ATTR_VOLUME_UUID).
> + */
> +struct fsinfo_volume_uuid {
> +	__u8	uuid[16];
> +};
> +
> +#define FSINFO_ATTR_VOLUME_UUID__STRUCT struct fsinfo_volume_uuid
> +
> +#endif /* _UAPI_LINUX_FSINFO_H */
> diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
> index 3e1c5c9d2efe..f72a9e4ddc9a 100644
> --- a/kernel/sys_ni.c
> +++ b/kernel/sys_ni.c
> @@ -51,6 +51,7 @@ COND_SYSCALL_COMPAT(io_pgetevents);
>  COND_SYSCALL(io_uring_setup);
>  COND_SYSCALL(io_uring_enter);
>  COND_SYSCALL(io_uring_register);
> +COND_SYSCALL(fsinfo);
>  
>  /* fs/xattr.c */
>  
> diff --git a/samples/vfs/Makefile b/samples/vfs/Makefile
> index 00b6824f9237..d63af5106fc2 100644
> --- a/samples/vfs/Makefile
> +++ b/samples/vfs/Makefile
> @@ -1,5 +1,5 @@
>  # SPDX-License-Identifier: GPL-2.0-only
> -userprogs := test-fsmount test-statx
> +userprogs := test-fsinfo test-fsmount test-statx
>  always-y := $(userprogs)
>  
>  userccflags += -I usr/include
> diff --git a/samples/vfs/test-fsinfo.c b/samples/vfs/test-fsinfo.c
> new file mode 100644
> index 000000000000..934b25399ffe
> --- /dev/null
> +++ b/samples/vfs/test-fsinfo.c
> @@ -0,0 +1,646 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/* Test the fsinfo() system call
> + *
> + * Copyright (C) 2020 Red Hat, Inc. All Rights Reserved.
> + * Written by David Howells ([e-mail])
> + */
> +
> +#define _GNU_SOURCE
> +#define _ATFILE_SOURCE
> +#include <stdbool.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <stdint.h>
> +#include <string.h>
> +#include <unistd.h>
> +#include <ctype.h>
> +#include <errno.h>
> +#include <time.h>
> +#include <math.h>
> +#include <fcntl.h>
> +#include <sys/syscall.h>
> +#include <linux/fsinfo.h>
> +#include <linux/socket.h>
> +#include <sys/stat.h>
> +#include <arpa/inet.h>
> +
> +#ifndef __NR_fsinfo
> +#define __NR_fsinfo -1
> +#endif
> +
> +static bool debug = 0;
> +static bool list_last;
> +
> +static __attribute__((unused))
> +ssize_t fsinfo(int dfd, const char *filename,
> +	       struct fsinfo_params *params, size_t params_size,
> +	       void *result_buffer, size_t result_buf_size)
> +{
> +	return syscall(__NR_fsinfo, dfd, filename,
> +		       params, params_size,
> +		       result_buffer, result_buf_size);
> +}
> +
> +struct fsinfo_attribute {
> +	unsigned int		attr_id;
> +	enum fsinfo_value_type	type;
> +	unsigned int		size;
> +	const char		*name;
> +	void (*dump)(void *reply, unsigned int size);
> +};
> +
> +static const struct fsinfo_attribute fsinfo_attributes[];
> +
> +static ssize_t get_fsinfo(const char *, const char *, struct fsinfo_params *, void **);
> +
> +static void dump_hex(FILE *f, unsigned char *data, int from, int to)
> +{
> +	unsigned offset, col = 0;
> +	bool print_offset = true;
> +
> +	for (offset = from; offset < to; offset++) {
> +		if (print_offset) {
> +			fprintf(f, "%04x: ", offset);
> +			print_offset = 0;
> +		}
> +		fprintf(f, "%02x", data[offset]);
> +		col++;
> +		if ((col & 3) == 0) {
> +			if ((col & 15) == 0) {
> +				fprintf(f, "\n");
> +				print_offset = 1;
> +			} else {
> +				fprintf(f, " ");
> +			}
> +		}
> +	}
> +
> +	if (!print_offset)
> +		fprintf(f, "\n");
> +}
> +
> +static void dump_attribute_info(void *reply, unsigned int size)
> +{
> +	struct fsinfo_attribute_info *attr_info = reply;
> +	const struct fsinfo_attribute *attr;
> +	char type[32], val_size[32];
> +
> +	switch (attr_info->type) {
> +	case FSINFO_TYPE_VSTRUCT:	strcpy(type, "V-STRUCT");	break;
> +	case FSINFO_TYPE_STRING:	strcpy(type, "STRING");		break;
> +	case FSINFO_TYPE_OPAQUE:	strcpy(type, "OPAQUE");		break;
> +	case FSINFO_TYPE_LIST:		strcpy(type, "LIST");		break;
> +	default:
> +		sprintf(type, "type-%x", attr_info->type);
> +		break;
> +	}
> +
> +	if (attr_info->flags & FSINFO_FLAGS_N)
> +		strcat(type, " x N");
> +	else if (attr_info->flags & FSINFO_FLAGS_NM)
> +		strcat(type, " x NM");
> +
> +	for (attr = fsinfo_attributes; attr->name; attr++)
> +		if (attr->attr_id == attr_info->attr_id)
> +			break;
> +
> +	if (attr_info->size)
> +		sprintf(val_size, "%u", attr_info->size);
> +	else
> +		strcpy(val_size, "-");
> +
> +	printf("%8x %-12s %08x %5s %s\n",
> +	       attr_info->attr_id,
> +	       type,
> +	       attr_info->flags,
> +	       val_size,
> +	       attr->name ? attr->name : "");
> +}
> +
> +static void dump_fsinfo_generic_statfs(void *reply, unsigned int size)
> +{
> +	struct fsinfo_statfs *f = reply;
> +
> +	printf("\n");
> +	printf("\tblocks       : n=%llu fr=%llu av=%llu\n",
> +	       (unsigned long long)f->f_blocks.lo,
> +	       (unsigned long long)f->f_bfree.lo,
> +	       (unsigned long long)f->f_bavail.lo);
> +
> +	printf("\tfiles        : n=%llu fr=%llu av=%llu\n",
> +	       (unsigned long long)f->f_files.lo,
> +	       (unsigned long long)f->f_ffree.lo,
> +	       (unsigned long long)f->f_favail.lo);
> +	printf("\tbsize        : %llu\n",
> +	       (unsigned long long)f->f_bsize);
> +	printf("\tfrsize       : %llu\n",
> +	       (unsigned long long)f->f_frsize);
> +}
> +
> +static void dump_fsinfo_generic_ids(void *reply, unsigned int size)
> +{
> +	struct fsinfo_ids *f = reply;
> +
> +	printf("\n");
> +	printf("\tdev          : %02x:%02x\n", f->f_dev_major, f->f_dev_minor);
> +	printf("\tfs           : type=%x name=%s\n", f->f_fstype, f->f_fs_name);
> +	printf("\tfsid         : %llx\n", (unsigned long long)f->f_fsid);
> +	printf("\tsbid         : %llx\n", (unsigned long long)f->f_sb_id);
> +}
> +
> +static void dump_fsinfo_generic_limits(void *reply, unsigned int size)
> +{
> +	struct fsinfo_limits *f = reply;
> +
> +	printf("\n");
> +	printf("\tmax file size: %llx%016llx\n",
> +	       (unsigned long long)f->max_file_size.hi,
> +	       (unsigned long long)f->max_file_size.lo);
> +	printf("\tmax ino      : %llx%016llx\n",
> +	       (unsigned long long)f->max_ino.hi,
> +	       (unsigned long long)f->max_ino.lo);
> +	printf("\tmax ids      : u=%llx g=%llx p=%llx\n",
> +	       (unsigned long long)f->max_uid,
> +	       (unsigned long long)f->max_gid,
> +	       (unsigned long long)f->max_projid);
> +	printf("\tmax dev      : maj=%x min=%x\n",
> +	       f->max_dev_major, f->max_dev_minor);
> +	printf("\tmax links    : %llx\n",
> +	       (unsigned long long)f->max_hard_links);
> +	printf("\tmax xattr    : n=%x b=%llx\n",
> +	       f->max_xattr_name_len,
> +	       (unsigned long long)f->max_xattr_body_len);
> +	printf("\tmax len      : file=%x sym=%x\n",
> +	       f->max_filename_len, f->max_symlink_len);
> +}
> +
> +static void dump_fsinfo_generic_supports(void *reply, unsigned int size)
> +{
> +	struct fsinfo_supports *f = reply;
> +
> +	printf("\n");
> +	printf("\tstx_attr     : %llx\n", (unsigned long long)f->stx_attributes);
> +	printf("\tstx_mask     : %x\n", f->stx_mask);
> +	printf("\tfs_ioc_*flags: get=%x set=%x clr=%x\n",
> +	       f->fs_ioc_getflags, f->fs_ioc_setflags_set, f->fs_ioc_setflags_clear);
> +	printf("\tfs_ioc_*xattr: fsx_xflags: get=%x set=%x clr=%x\n",
> +	       f->fs_ioc_fsgetxattr_xflags,
> +	       f->fs_ioc_fssetxattr_xflags_set,
> +	       f->fs_ioc_fssetxattr_xflags_clear);
> +	printf("\twin_fattrs   : %x\n", f->win_file_attrs);
> +}
> +
> +static void print_time(struct fsinfo_timestamp_one *t, char stamp)
> +{
> +	printf("\t%ctime       : gran=%uE%d range=%llx-%llx\n",
> +	       stamp,
> +	       t->gran_mantissa, t->gran_exponent,
> +	       (long long)t->minimum, (long long)t->maximum);
> +}
> +
> +static void dump_fsinfo_generic_timestamp_info(void *reply, unsigned int size)
> +{
> +	struct fsinfo_timestamp_info *f = reply;
> +
> +	printf("\n");
> +	print_time(&f->atime, 'a');
> +	print_time(&f->mtime, 'm');
> +	print_time(&f->ctime, 'c');
> +	print_time(&f->btime, 'b');
> +}
> +
> +static void dump_fsinfo_generic_volume_uuid(void *reply, unsigned int size)
> +{
> +	struct fsinfo_volume_uuid *f = reply;
> +
> +	printf("%02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x"
> +	       "-%02x%02x%02x%02x%02x%02x\n",
> +	       f->uuid[ 0], f->uuid[ 1],
> +	       f->uuid[ 2], f->uuid[ 3],
> +	       f->uuid[ 4], f->uuid[ 5],
> +	       f->uuid[ 6], f->uuid[ 7],
> +	       f->uuid[ 8], f->uuid[ 9],
> +	       f->uuid[10], f->uuid[11],
> +	       f->uuid[12], f->uuid[13],
> +	       f->uuid[14], f->uuid[15]);
> +}
> +
> +static void dump_string(void *reply, unsigned int size)
> +{
> +	char *s = reply, *p;
> +	bool nl = false, last_nl = false;
> +
> +	p = s;
> +	if (size >= 4096) {
> +		size = 4096;
> +		p[4092] = '.';
> +		p[4093] = '.';
> +		p[4094] = '.';
> +		p[4095] = 0;
> +	} else {
> +		p[size] = 0;
> +	}
> +
> +	for (p = s; *p; p++) {
> +		if (*p == '\n') {
> +			last_nl = nl = true;
> +			continue;
> +		}
> +		last_nl = false;
> +		if (!isprint(*p) && *p != '\t')
> +			*p = '?';
> +	}
> +
> +	if (nl)
> +		putchar('\n');
> +	printf("%s", s);
> +	if (!last_nl)
> +		putchar('\n');
> +}
> +
> +#define dump_fsinfo_meta_attribute_info		(void *)0x123
> +#define dump_fsinfo_meta_attributes		(void *)0x123
> +
> +/*
> + *
> + */
> +#define __FSINFO(A, T, S, G, F, N)					\
> +	{ .attr_id = A, .type = T, .size = S, .name = N, .dump = dump_##G }
> +
> +#define _FSINFO(A,T,S,G,N)	__FSINFO(A, T, S, G, 0, N)
> +#define _FSINFO_N(A,T,S,G,N)	__FSINFO(A, T, S, G, FSINFO_FLAGS_N, N)
> +#define _FSINFO_NM(A,T,S,G,N)	__FSINFO(A, T, S, G, FSINFO_FLAGS_NM, N)
> +
> +#define _FSINFO_VSTRUCT(A,S,G,N)    _FSINFO   (A, FSINFO_TYPE_VSTRUCT, sizeof(S), G, N)
> +#define _FSINFO_VSTRUCT_N(A,S,G,N)  _FSINFO_N (A, FSINFO_TYPE_VSTRUCT, sizeof(S), G, N)
> +#define _FSINFO_VSTRUCT_NM(A,S,G,N) _FSINFO_NM(A, FSINFO_TYPE_VSTRUCT, sizeof(S), G, N)
> +
> +#define FSINFO_VSTRUCT(A,G)	_FSINFO_VSTRUCT   (A, A##__STRUCT, G, #A)
> +#define FSINFO_VSTRUCT_N(A,G)	_FSINFO_VSTRUCT_N (A, A##__STRUCT, G, #A)
> +#define FSINFO_VSTRUCT_NM(A,G)	_FSINFO_VSTRUCT_NM(A, A##__STRUCT, G, #A)
> +#define FSINFO_STRING(A,G)	_FSINFO   (A, FSINFO_TYPE_STRING, 0, G, #A)
> +#define FSINFO_STRING_N(A,G)	_FSINFO_N (A, FSINFO_TYPE_STRING, 0, G, #A)
> +#define FSINFO_STRING_NM(A,G)	_FSINFO_NM(A, FSINFO_TYPE_STRING, 0, G, #A)
> +#define FSINFO_OPAQUE(A,G)	_FSINFO   (A, FSINFO_TYPE_OPAQUE, 0, G, #A)
> +#define FSINFO_LIST(A,G)	_FSINFO   (A, FSINFO_TYPE_LIST, sizeof(A##__STRUCT), G, #A)
> +#define FSINFO_LIST_N(A,G)	_FSINFO_N (A, FSINFO_TYPE_LIST, sizeof(A##__STRUCT), G, #A)
> +
> +static const struct fsinfo_attribute fsinfo_attributes[] = {
> +	FSINFO_VSTRUCT	(FSINFO_ATTR_STATFS,		fsinfo_generic_statfs),
> +	FSINFO_VSTRUCT	(FSINFO_ATTR_IDS,		fsinfo_generic_ids),
> +	FSINFO_VSTRUCT	(FSINFO_ATTR_LIMITS,		fsinfo_generic_limits),
> +	FSINFO_VSTRUCT	(FSINFO_ATTR_SUPPORTS,		fsinfo_generic_supports),
> +	FSINFO_VSTRUCT	(FSINFO_ATTR_TIMESTAMP_INFO,	fsinfo_generic_timestamp_info),
> +	FSINFO_STRING	(FSINFO_ATTR_VOLUME_ID,		string),
> +	FSINFO_VSTRUCT	(FSINFO_ATTR_VOLUME_UUID,	fsinfo_generic_volume_uuid),
> +	FSINFO_STRING	(FSINFO_ATTR_VOLUME_NAME,	string),
> +	FSINFO_VSTRUCT_N(FSINFO_ATTR_FSINFO_ATTRIBUTE_INFO, fsinfo_meta_attribute_info),
> +	FSINFO_LIST	(FSINFO_ATTR_FSINFO_ATTRIBUTES,	fsinfo_meta_attributes),
> +	{}
> +};
> +
> +static __attribute__((noreturn))
> +void bad_value(const char *what,
> +	       struct fsinfo_params *params,
> +	       const struct fsinfo_attribute *attr,
> +	       const struct fsinfo_attribute_info *attr_info,
> +	       void *reply, unsigned int size)
> +{
> +	printf("\n");
> +	fprintf(stderr, "%s %s{%u}{%u} t=%x f=%x s=%x\n",
> +		what, attr->name, params->Nth, params->Mth,
> +		attr_info->type, attr_info->flags, attr_info->size);
> +	fprintf(stderr, "size=%u\n", size);
> +	dump_hex(stderr, reply, 0, size);
> +	exit(1);
> +}
> +
> +static void dump_value(unsigned int attr_id,
> +		       const struct fsinfo_attribute *attr,
> +		       const struct fsinfo_attribute_info *attr_info,
> +		       void *reply, unsigned int size)
> +{
> +	if (!attr || !attr->dump) {
> +		printf("<no dumper>\n");
> +		return;
> +	}
> +
> +	if (attr->type == FSINFO_TYPE_VSTRUCT && size < attr->size) {
> +		printf("<short data %u/%u>\n", size, attr->size);
> +		return;
> +	}
> +
> +	attr->dump(reply, size);
> +}
> +
> +static void dump_list(unsigned int attr_id,
> +		      const struct fsinfo_attribute *attr,
> +		      const struct fsinfo_attribute_info *attr_info,
> +		      void *reply, unsigned int size)
> +{
> +	size_t elem_size = attr_info->size;
> +	unsigned int ix = 0;
> +
> +	printf("\n");
> +	if (!attr || !attr->dump) {
> +		printf("<no dumper>\n");
> +		return;
> +	}
> +
> +	if (attr->type == FSINFO_TYPE_VSTRUCT && size < attr->size) {
> +		printf("<short data %u/%u>\n", size, attr->size);
> +		return;
> +	}
> +
> +	list_last = false;
> +	while (size >= elem_size) {
> +		printf("\t[%02x] ", ix);
> +		if (size == elem_size)
> +			list_last = true;
> +		attr->dump(reply, size);
> +		reply += elem_size;
> +		size -= elem_size;
> +		ix++;
> +	}
> +}
> +
> +/*
> + * Call fsinfo, expanding the buffer as necessary.
> + */
> +static ssize_t get_fsinfo(const char *file, const char *name,
> +			  struct fsinfo_params *params, void **_r)
> +{
> +	ssize_t ret;
> +	size_t buf_size = 4096;
> +	void *r;
> +
> +	for (;;) {
> +		r = malloc(buf_size);
> +		if (!r) {
> +			perror("malloc");
> +			exit(1);
> +		}
> +		memset(r, 0xbd, buf_size);
> +
> +		errno = 0;
> +		ret = fsinfo(AT_FDCWD, file, params, sizeof(*params), r, buf_size - 1);
> +		if (ret == -1)
> +			goto error;
> +
> +		if (ret <= buf_size - 1)
> +			break;
> +		buf_size = (ret + 4096 - 1) & ~(4096 - 1);
> +	}
> +
> +	if (debug)
> +		printf("fsinfo(%s,%s,%u,%u) = %zd\n",
> +		       file, name, params->Nth, params->Mth, ret);
> +
> +	((char *)r)[ret] = 0;
> +	*_r = r;
> +	return ret;
> +
> +error:
> +	*_r = NULL;
> +	free(r);
> +	if (debug)
> +		printf("fsinfo(%s,%s,%u,%u) = %m\n",
> +		       file, name, params->Nth, params->Mth);
> +	return ret;
> +}
> +
> +/*
> + * Try one subinstance of an attribute.
> + */
> +static int try_one(const char *file, struct fsinfo_params *params,
> +		   const struct fsinfo_attribute_info *attr_info, bool raw)
> +{
> +	const struct fsinfo_attribute *attr;
> +	const char *name;
> +	size_t size = 4096;
> +	char namebuf[32];
> +	void *r;
> +
> +	for (attr = fsinfo_attributes; attr->name; attr++) {
> +		if (attr->attr_id == params->request) {
> +			name = attr->name;
> +			if (strncmp(name, "fsinfo_generic_", 15) == 0)
> +				name += 15;
> +			goto found;
> +		}
> +	}
> +
> +	sprintf(namebuf, "<unknown-%x>", params->request);
> +	name = namebuf;
> +	attr = NULL;
> +
> +found:
> +	size = get_fsinfo(file, name, params, &r);
> +
> +	if (size == -1) {
> +		if (errno == ENODATA) {
> +			if (!(attr_info->flags & (FSINFO_FLAGS_N | FSINFO_FLAGS_NM)) &&
> +			    params->Nth == 0 && params->Mth == 0)
> +				bad_value("Unexpected ENODATA",
> +					  params, attr, attr_info, r, size);
> +			free(r);
> +			return (params->Mth == 0) ? 2 : 1;
> +		}
> +		if (errno == EOPNOTSUPP) {
> +			if (params->Nth > 0 || params->Mth > 0)
> +				bad_value("Should return ENODATA",
> +					  params, attr, attr_info, r, size);
> +			//printf("\e[33m%s\e[m: <not supported>\n",
> +			//       fsinfo_attr_names[attr]);
> +			free(r);
> +			return 2;
> +		}
> +		perror(file);
> +		exit(1);
> +	}
> +
> +	if (raw) {
> +		if (size > 4096)
> +			size = 4096;
> +		dump_hex(stdout, r, 0, size);
> +		free(r);
> +		return 0;
> +	}
> +
> +	switch (attr_info->flags & (FSINFO_FLAGS_N | FSINFO_FLAGS_NM)) {
> +	case 0:
> +		printf("\e[33m%s\e[m: ", name);
> +		break;
> +	case FSINFO_FLAGS_N:
> +		printf("\e[33m%s{%u}\e[m: ", name, params->Nth);
> +		break;
> +	case FSINFO_FLAGS_NM:
> +		printf("\e[33m%s{%u,%u}\e[m: ", name, params->Nth, params->Mth);
> +		break;
> +	}
> +
> +	switch (attr_info->type) {
> +	case FSINFO_TYPE_STRING:
> +		if (size == 0 || ((char *)r)[size - 1] != 0)
> +			bad_value("Unterminated string",
> +				  params, attr, attr_info, r, size);
> +	case FSINFO_TYPE_VSTRUCT:
> +	case FSINFO_TYPE_OPAQUE:
> +		dump_value(params->request, attr, attr_info, r, size);
> +		free(r);
> +		return 0;
> +
> +	case FSINFO_TYPE_LIST:
> +		dump_list(params->request, attr, attr_info, r, size);
> +		free(r);
> +		return 0;
> +
> +	default:
> +		bad_value("Fishy type", params, attr, attr_info, r, size);
> +	}
> +}
> +
> +static int cmp_u32(const void *a, const void *b)
> +{
> +	return *(const int *)a - *(const int *)b;
> +}
> +
> +/*
> + *
> + */
> +int main(int argc, char **argv)
> +{
> +	struct fsinfo_attribute_info attr_info;
> +	struct fsinfo_params params = {
> +		.at_flags	= AT_SYMLINK_NOFOLLOW,
> +		.flags		= FSINFO_FLAGS_QUERY_PATH,
> +	};
> +	unsigned int *attrs, ret, nr, i;
> +	bool meta = false;
> +	int raw = 0, opt, Nth, Mth;
> +
> +	while ((opt = getopt(argc, argv, "Madlr"))) {
> +		switch (opt) {
> +		case 'M':
> +			meta = true;
> +			continue;
> +		case 'a':
> +			params.at_flags |= AT_NO_AUTOMOUNT;
> +			params.flags = FSINFO_FLAGS_QUERY_PATH;
> +			continue;
> +		case 'd':
> +			debug = true;
> +			continue;
> +		case 'l':
> +			params.at_flags &= ~AT_SYMLINK_NOFOLLOW;
> +			params.flags = FSINFO_FLAGS_QUERY_PATH;
> +			continue;
> +		case 'r':
> +			raw = 1;
> +			continue;
> +		}
> +		break;
> +	}
> +
> +	argc -= optind;
> +	argv += optind;
> +
> +	if (argc != 1) {
> +		printf("Format: test-fsinfo [-Madlr] <path>\n");
> +		exit(2);
> +	}
> +
> +	/* Retrieve a list of supported attribute IDs */
> +	params.request = FSINFO_ATTR_FSINFO_ATTRIBUTES;
> +	params.Nth = 0;
> +	params.Mth = 0;
> +	ret = get_fsinfo(argv[0], "attributes", &params, (void **)&attrs);
> +	if (ret == -1) {
> +		fprintf(stderr, "Unable to get attribute list: %m\n");
> +		exit(1);
> +	}
> +
> +	if (ret % sizeof(attrs[0])) {
> +		fprintf(stderr, "Bad length of attribute list (0x%x)\n", ret);
> +		exit(2);
> +	}
> +
> +	nr = ret / sizeof(attrs[0]);
> +	qsort(attrs, nr, sizeof(attrs[0]), cmp_u32);
> +
> +	if (meta) {
> +		printf("ATTR ID  TYPE         FLAGS    SIZE  NAME\n");
> +		printf("======== ============ ======== ===== =========\n");
> +		for (i = 0; i < nr; i++) {
> +			params.request = FSINFO_ATTR_FSINFO_ATTRIBUTE_INFO;
> +			params.Nth = attrs[i];
> +			params.Mth = 0;
> +			ret = fsinfo(AT_FDCWD, argv[0],
> +				     &params, sizeof(params),
> +				     &attr_info, sizeof(attr_info));
> +			if (ret == -1) {
> +				fprintf(stderr, "Can't get info for attribute %x: %m\n", attrs[i]);
> +				exit(1);
> +			}
> +
> +			dump_attribute_info(&attr_info, ret);
> +		}
> +		exit(0);
> +	}
> +
> +	for (i = 0; i < nr; i++) {
> +		params.request = FSINFO_ATTR_FSINFO_ATTRIBUTE_INFO;
> +		params.Nth = attrs[i];
> +		params.Mth = 0;
> +		ret = fsinfo(AT_FDCWD, argv[0],
> +			     &params, sizeof(params),
> +			     &attr_info, sizeof(attr_info));
> +		if (ret == -1) {
> +			fprintf(stderr, "Can't get info for attribute %x: %m\n", attrs[i]);
> +			exit(1);
> +		}
> +
> +		if (attrs[i] == FSINFO_ATTR_FSINFO_ATTRIBUTE_INFO ||
> +		    attrs[i] == FSINFO_ATTR_FSINFO_ATTRIBUTES)
> +			continue;
> +
> +		if (attrs[i] != attr_info.attr_id) {
> +			fprintf(stderr, "ID for %03x returned %03x\n",
> +				attrs[i], attr_info.attr_id);
> +			break;
> +		}
> +		Nth = 0;
> +		do {
> +			Mth = 0;
> +			do {
> +				params.request = attrs[i];
> +				params.Nth = Nth;
> +				params.Mth = Mth;
> +
> +				switch (try_one(argv[0], &params, &attr_info, raw)) {
> +				case 0:
> +					continue;
> +				case 1:
> +					goto done_M;
> +				case 2:
> +					goto done_N;
> +				}
> +			} while (++Mth < 100);
> +
> +		done_M:
> +			if (Mth >= 100) {
> +				fprintf(stderr, "Fishy: Mth %x[%u][%u]\n", attrs[i], Nth, Mth);
> +				break;
> +			}
> +
> +		} while (++Nth < 100);
> +
> +	done_N:
> +		if (Nth >= 100) {
> +			fprintf(stderr, "Fishy: Nth %x[%u]\n", attrs[i], Nth);
> +			break;
> +		}
> +	}
> +
> +	return 0;
> +}
> 
>

David Howells Aug. 4, 2020, 11:34 a.m. UTC | #2

Miklos Szeredi <[e-mail]> wrote:

> > 		__u32	Mth;
> 
> The Mth field seems to be unused in this patchset.  Since the struct is
> extensible, I guess there's no point in adding it now.

Yeah - I was using it to index through the server address lists for network
filesystems (ie. the Mth address of the Nth server), but I've dropped the nfs
patch and made afs return an array of addresses for the Nth server since the
address list can get reordered.

Ordinarily, I'd just take it out, but I don't want to cause the patchset to
get dropped for yet another merge cycle :-/

> > +#define FSINFO_ATTR_FSINFO_ATTRIBUTE_INFO 0x100	/* Information about attr N (for path) */
> > +#define FSINFO_ATTR_FSINFO_ATTRIBUTES	0x101	/* List of supported attrs (for path) */
> 
> I think it would make sense to move the actual attributes to a separate patch
> and leave this just being the infrastructure.

Maybe.  If there are no attributes, then it makes it a bit hard to test.

> > +struct fsinfo_u128 {
> ...
> 
> Shouldn't this belong in <linux/types.h>?

Maybe.  Ideally, I'd use a proper C type rather than a struct.

> Is there a reason these are 128 wide fields?  Are we approaching the limits of
> 64bits?

Dave Chinner was talking at LSF a couple of years ago, IIRC, about looking
beyond the 16 Exa limit in XFS.  I've occasionally talked to people who have
multi-Peta data sets in AFS or whatever they were using, streamed from science
experiments, so the limit isn't necessarily all *that* far off.

> > +struct fsinfo_limits {
> > +	struct fsinfo_u128 max_file_size;	/* Maximum file size */
> > +	struct fsinfo_u128 max_ino;		/* Maximum inode number */
> 
> Again, what's the reason.  AFACT we are not yet worried about overflowing 64
> bits.  Future proofing is good, but there has to be some rules and reasons
> behind the decisions.

This is cheap to do.  This information is expected to be static for the
lifetime a superblock and, for most filesystems, of the running kernel, so
simply copying it with memcpy() from rodata is going to suffice most of the
time.

But don't worry - 640K is sufficient for everyone ;-)

David

Michael Kerrisk (man-pages) Aug. 27, 2020, 11:27 a.m. UTC | #3

Hello David,

On Mon, 3 Aug 2020 at 15:37, David Howells <[e-mail]> wrote:
>
> Add a system call to allow filesystem information to be queried.  A request
> value can be given to indicate the desired attribute.  Support is provided
> for enumerating multi-value attributes.

Do we have an up to date manual page for this system call?

Could you please (re)post to the same CC as this mail, plus linux-man@?

Thanks,

Michael

Patch

diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl
index b6cf8403da35..984abd1ac058 100644
--- a/arch/alpha/kernel/syscalls/syscall.tbl
+++ b/arch/alpha/kernel/syscalls/syscall.tbl
@@ -479,3 +479,4 @@ 
 548	common	pidfd_getfd			sys_pidfd_getfd
 549	common	faccessat2			sys_faccessat2
 550	common	watch_mount			sys_watch_mount
+551	common	fsinfo				sys_fsinfo
diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl
index 27cc1f53f4a0..bd791f91f5bb 100644
--- a/arch/arm/tools/syscall.tbl
+++ b/arch/arm/tools/syscall.tbl
@@ -453,3 +453,4 @@ 
 438	common	pidfd_getfd			sys_pidfd_getfd
 439	common	faccessat2			sys_faccessat2
 440	common	watch_mount			sys_watch_mount
+441	common	fsinfo				sys_fsinfo
diff --git a/arch/arm64/include/asm/unistd.h b/arch/arm64/include/asm/unistd.h
index b3b2019f8d16..86a9d7b3eabe 100644
--- a/arch/arm64/include/asm/unistd.h
+++ b/arch/arm64/include/asm/unistd.h
@@ -38,7 +38,7 @@ 
 #define __ARM_NR_compat_set_tls		(__ARM_NR_COMPAT_BASE + 5)
 #define __ARM_NR_COMPAT_END		(__ARM_NR_COMPAT_BASE + 0x800)
 
-#define __NR_compat_syscalls		441
+#define __NR_compat_syscalls		442
 #endif
 
 #define __ARCH_WANT_SYS_CLONE
diff --git a/arch/arm64/include/asm/unistd32.h b/arch/arm64/include/asm/unistd32.h
index 4f9cf98cdf0f..bd78eb2c487a 100644
--- a/arch/arm64/include/asm/unistd32.h
+++ b/arch/arm64/include/asm/unistd32.h
@@ -887,6 +887,8 @@  __SYSCALL(__NR_pidfd_getfd, sys_pidfd_getfd)
 __SYSCALL(__NR_faccessat2, sys_faccessat2)
 #define __NR_watch_mount 440
 __SYSCALL(__NR_watch_mount, sys_watch_mount)
+#define __NR_fsinfo 441
+__SYSCALL(__NR_fsinfo, sys_fsinfo)
 
 /*
  * Please add new compat syscalls above this comment and update
diff --git a/arch/ia64/kernel/syscalls/syscall.tbl b/arch/ia64/kernel/syscalls/syscall.tbl
index fc6d87903781..09d144487b7d 100644
--- a/arch/ia64/kernel/syscalls/syscall.tbl
+++ b/arch/ia64/kernel/syscalls/syscall.tbl
@@ -360,3 +360,4 @@ 
 438	common	pidfd_getfd			sys_pidfd_getfd
 439	common	faccessat2			sys_faccessat2
 440	common	watch_mount			sys_watch_mount
+441	common	fsinfo				sys_fsinfo
diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl
index c671aa0e4d25..1bdc26af3c54 100644
--- a/arch/m68k/kernel/syscalls/syscall.tbl
+++ b/arch/m68k/kernel/syscalls/syscall.tbl
@@ -439,3 +439,4 @@ 
 438	common	pidfd_getfd			sys_pidfd_getfd
 439	common	faccessat2			sys_faccessat2
 440	common	watch_mount			sys_watch_mount
+441	common	fsinfo				sys_fsinfo
diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl
index 65cc53f129ef..fb8543122904 100644
--- a/arch/microblaze/kernel/syscalls/syscall.tbl
+++ b/arch/microblaze/kernel/syscalls/syscall.tbl
@@ -445,3 +445,4 @@ 
 438	common	pidfd_getfd			sys_pidfd_getfd
 439	common	faccessat2			sys_faccessat2
 440	common	watch_mount			sys_watch_mount
+441	common	fsinfo				sys_fsinfo
diff --git a/arch/mips/kernel/syscalls/syscall_n32.tbl b/arch/mips/kernel/syscalls/syscall_n32.tbl
index 7f034a239930..b8362bd6bd4a 100644
--- a/arch/mips/kernel/syscalls/syscall_n32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n32.tbl
@@ -378,3 +378,4 @@ 
 438	n32	pidfd_getfd			sys_pidfd_getfd
 439	n32	faccessat2			sys_faccessat2
 440	n32	watch_mount			sys_watch_mount
+441	n32	fsinfo				sys_fsinfo
diff --git a/arch/mips/kernel/syscalls/syscall_n64.tbl b/arch/mips/kernel/syscalls/syscall_n64.tbl
index d39b90de3642..60ca4091d378 100644
--- a/arch/mips/kernel/syscalls/syscall_n64.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n64.tbl
@@ -354,3 +354,4 @@ 
 438	n64	pidfd_getfd			sys_pidfd_getfd
 439	n64	faccessat2			sys_faccessat2
 440	n64	watch_mount			sys_watch_mount
+441	n64	fsinfo				sys_fsinfo
diff --git a/arch/mips/kernel/syscalls/syscall_o32.tbl b/arch/mips/kernel/syscalls/syscall_o32.tbl
index 09f426cb45b1..07aea9379ca0 100644
--- a/arch/mips/kernel/syscalls/syscall_o32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_o32.tbl
@@ -427,3 +427,4 @@ 
 438	o32	pidfd_getfd			sys_pidfd_getfd
 439	o32	faccessat2			sys_faccessat2
 440	o32	watch_mount			sys_watch_mount
+441	o32	fsinfo				sys_fsinfo
diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl
index 52ff3454baa1..f8060767f11a 100644
--- a/arch/parisc/kernel/syscalls/syscall.tbl
+++ b/arch/parisc/kernel/syscalls/syscall.tbl
@@ -437,3 +437,4 @@ 
 438	common	pidfd_getfd			sys_pidfd_getfd
 439	common	faccessat2			sys_faccessat2
 440	common	watch_mount			sys_watch_mount
+441	common	fsinfo				sys_fsinfo
diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl
index 10b7ed3c7a1b..3036bf1336d2 100644
--- a/arch/powerpc/kernel/syscalls/syscall.tbl
+++ b/arch/powerpc/kernel/syscalls/syscall.tbl
@@ -529,3 +529,4 @@ 
 438	common	pidfd_getfd			sys_pidfd_getfd
 439	common	faccessat2			sys_faccessat2
 440	common	watch_mount			sys_watch_mount
+441	common	fsinfo				sys_fsinfo
diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl
index 86f317bf52df..c0a111fdb3ce 100644
--- a/arch/s390/kernel/syscalls/syscall.tbl
+++ b/arch/s390/kernel/syscalls/syscall.tbl
@@ -442,3 +442,4 @@ 
 438  common	pidfd_getfd		sys_pidfd_getfd			sys_pidfd_getfd
 439  common	faccessat2		sys_faccessat2			sys_faccessat2
 440	common	watch_mount		sys_watch_mount			sys_watch_mount
+441	common	fsinfo			sys_fsinfo			sys_fsinfo
diff --git a/arch/sh/kernel/syscalls/syscall.tbl b/arch/sh/kernel/syscalls/syscall.tbl
index 0bb0f0b372c7..03b55c32441f 100644
--- a/arch/sh/kernel/syscalls/syscall.tbl
+++ b/arch/sh/kernel/syscalls/syscall.tbl
@@ -442,3 +442,4 @@ 
 438	common	pidfd_getfd			sys_pidfd_getfd
 439	common	faccessat2			sys_faccessat2
 440	common	watch_mount			sys_watch_mount
+441	common	fsinfo				sys_fsinfo
diff --git a/arch/sparc/kernel/syscalls/syscall.tbl b/arch/sparc/kernel/syscalls/syscall.tbl
index 369ab65c1e9a..a0144db9fb8c 100644
--- a/arch/sparc/kernel/syscalls/syscall.tbl
+++ b/arch/sparc/kernel/syscalls/syscall.tbl
@@ -485,3 +485,4 @@ 
 438	common	pidfd_getfd			sys_pidfd_getfd
 439	common	faccessat2			sys_faccessat2
 440	common	watch_mount			sys_watch_mount
+441	common	fsinfo				sys_fsinfo
diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index e760ba92c58d..edf90a2be0b9 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -444,3 +444,4 @@ 
 438	i386	pidfd_getfd		sys_pidfd_getfd
 439	i386	faccessat2		sys_faccessat2
 440	i386	watch_mount		sys_watch_mount
+441	i386	fsinfo			sys_fsinfo
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index 5b58621d4f75..ab0eda639d67 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -361,6 +361,7 @@ 
 438	common	pidfd_getfd		sys_pidfd_getfd
 439	common	faccessat2		sys_faccessat2
 440	common	watch_mount		sys_watch_mount
+441	common	fsinfo			sys_fsinfo
 
 #
 # x32-specific system call numbers start at 512 to avoid cache impact
diff --git a/arch/xtensa/kernel/syscalls/syscall.tbl b/arch/xtensa/kernel/syscalls/syscall.tbl
index 5b28ee39f70f..979013890caf 100644
--- a/arch/xtensa/kernel/syscalls/syscall.tbl
+++ b/arch/xtensa/kernel/syscalls/syscall.tbl
@@ -410,3 +410,4 @@ 
 438	common	pidfd_getfd			sys_pidfd_getfd
 439	common	faccessat2			sys_faccessat2
 440	common	watch_mount			sys_watch_mount
+441	common	fsinfo				sys_fsinfo
diff --git a/fs/Kconfig b/fs/Kconfig
index 1a55e56d5c54..df76451ab49a 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -15,6 +15,13 @@  config VALIDATE_FS_PARSER
 	  Enable this to perform validation of the parameter description for a
 	  filesystem when it is registered.
 
+config FSINFO
+	bool "Enable the fsinfo() system call"
+	help
+	  Enable the file system information querying system call to allow
+	  comprehensive information to be retrieved about a filesystem,
+	  superblock or mount object.
+
 if BLOCK
 
 config FS_IOMAP
diff --git a/fs/Makefile b/fs/Makefile
index dd0d87e2ef19..93a7f8047585 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -55,6 +55,7 @@  obj-$(CONFIG_COREDUMP)		+= coredump.o
 obj-$(CONFIG_SYSCTL)		+= drop_caches.o
 
 obj-$(CONFIG_FHANDLE)		+= fhandle.o
+obj-$(CONFIG_FSINFO)		+= fsinfo.o
 obj-y				+= iomap/
 
 obj-y				+= quota/
diff --git a/fs/fsinfo.c b/fs/fsinfo.c
new file mode 100644
index 000000000000..7d9c73e9cbde
--- /dev/null
+++ b/fs/fsinfo.c
@@ -0,0 +1,596 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/* Filesystem information query.
+ *
+ * Copyright (C) 2020 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells ([e-mail])
+ */
+#include <linux/syscalls.h>
+#include <linux/fs.h>
+#include <linux/file.h>
+#include <linux/mount.h>
+#include <linux/namei.h>
+#include <linux/statfs.h>
+#include <linux/security.h>
+#include <linux/uaccess.h>
+#include <linux/fsinfo.h>
+#include <uapi/linux/mount.h>
+#include "internal.h"
+
+/**
+ * fsinfo_opaque - Store opaque blob as an fsinfo attribute value.
+ * @s: The blob to store (may be NULL)
+ * @ctx: The parameter context
+ * @len: The length of the blob
+ */
+int fsinfo_opaque(const void *s, struct fsinfo_context *ctx, unsigned int len)
+{
+	void *p = ctx->buffer;
+	int ret = 0;
+
+	if (s) {
+		if (!ctx->want_size_only)
+			memcpy(p, s, len);
+		ret = len;
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL(fsinfo_opaque);
+
+/**
+ * fsinfo_string - Store a NUL-terminated string as an fsinfo attribute value.
+ * @s: The string to store (may be NULL)
+ * @ctx: The parameter context
+ */
+int fsinfo_string(const char *s, struct fsinfo_context *ctx)
+{
+	if (!s)
+		return 1;
+	return fsinfo_opaque(s, ctx, min_t(size_t, strlen(s) + 1, ctx->buf_size));
+}
+EXPORT_SYMBOL(fsinfo_string);
+
+/*
+ * Get basic filesystem stats from statfs.
+ */
+static int fsinfo_generic_statfs(struct path *path, struct fsinfo_context *ctx)
+{
+	struct fsinfo_statfs *p = ctx->buffer;
+	struct kstatfs buf;
+	int ret;
+
+	ret = vfs_statfs(path, &buf);
+	if (ret < 0)
+		return ret;
+
+	p->f_blocks.lo	= buf.f_blocks;
+	p->f_bfree.lo	= buf.f_bfree;
+	p->f_bavail.lo	= buf.f_bavail;
+	p->f_files.lo	= buf.f_files;
+	p->f_ffree.lo	= buf.f_ffree;
+	p->f_favail.lo	= buf.f_ffree;
+	p->f_bsize	= buf.f_bsize;
+	p->f_frsize	= buf.f_frsize;
+	return sizeof(*p);
+}
+
+static int fsinfo_generic_ids(struct path *path, struct fsinfo_context *ctx)
+{
+	struct fsinfo_ids *p = ctx->buffer;
+	struct super_block *sb;
+	struct kstatfs buf;
+	int ret;
+
+	ret = vfs_statfs(path, &buf);
+	if (ret < 0 && ret != -ENOSYS)
+		return ret;
+	if (ret == 0)
+		memcpy(&p->f_fsid, &buf.f_fsid, sizeof(p->f_fsid));
+
+	sb = path->dentry->d_sb;
+	p->f_fstype	= sb->s_magic;
+	p->f_dev_major	= MAJOR(sb->s_dev);
+	p->f_dev_minor	= MINOR(sb->s_dev);
+	p->f_sb_id	= sb->s_unique_id;
+	strlcpy(p->f_fs_name, sb->s_type->name, sizeof(p->f_fs_name));
+	return sizeof(*p);
+}
+
+int fsinfo_generic_limits(struct path *path, struct fsinfo_context *ctx)
+{
+	struct fsinfo_limits *p = ctx->buffer;
+	struct super_block *sb = path->dentry->d_sb;
+
+	p->max_file_size.hi	= 0;
+	p->max_file_size.lo	= sb->s_maxbytes;
+	p->max_ino.hi		= 0;
+	p->max_ino.lo		= UINT_MAX;
+	p->max_hard_links	= sb->s_max_links;
+	p->max_uid		= UINT_MAX;
+	p->max_gid		= UINT_MAX;
+	p->max_projid		= UINT_MAX;
+	p->max_filename_len	= NAME_MAX;
+	p->max_symlink_len	= PATH_MAX;
+	p->max_xattr_name_len	= XATTR_NAME_MAX;
+	p->max_xattr_body_len	= XATTR_SIZE_MAX;
+	p->max_dev_major	= 0xffffff;
+	p->max_dev_minor	= 0xff;
+	return sizeof(*p);
+}
+EXPORT_SYMBOL(fsinfo_generic_limits);
+
+int fsinfo_generic_supports(struct path *path, struct fsinfo_context *ctx)
+{
+	struct fsinfo_supports *p = ctx->buffer;
+	struct super_block *sb = path->dentry->d_sb;
+
+	p->stx_mask = STATX_BASIC_STATS;
+	if (sb->s_d_op && sb->s_d_op->d_automount)
+		p->stx_attributes |= STATX_ATTR_AUTOMOUNT;
+	return sizeof(*p);
+}
+EXPORT_SYMBOL(fsinfo_generic_supports);
+
+static const struct fsinfo_timestamp_info fsinfo_default_timestamp_info = {
+	.atime = {
+		.minimum	= S64_MIN,
+		.maximum	= S64_MAX,
+		.gran_mantissa	= 1,
+		.gran_exponent	= 0,
+	},
+	.mtime = {
+		.minimum	= S64_MIN,
+		.maximum	= S64_MAX,
+		.gran_mantissa	= 1,
+		.gran_exponent	= 0,
+	},
+	.ctime = {
+		.minimum	= S64_MIN,
+		.maximum	= S64_MAX,
+		.gran_mantissa	= 1,
+		.gran_exponent	= 0,
+	},
+	.btime = {
+		.minimum	= S64_MIN,
+		.maximum	= S64_MAX,
+		.gran_mantissa	= 1,
+		.gran_exponent	= 0,
+	},
+};
+
+int fsinfo_generic_timestamp_info(struct path *path, struct fsinfo_context *ctx)
+{
+	struct fsinfo_timestamp_info *p = ctx->buffer;
+	struct super_block *sb = path->dentry->d_sb;
+	s8 exponent;
+
+	*p = fsinfo_default_timestamp_info;
+
+	if (sb->s_time_gran < 1000000000) {
+		if (sb->s_time_gran < 1000)
+			exponent = -9;
+		else if (sb->s_time_gran < 1000000)
+			exponent = -6;
+		else
+			exponent = -3;
+
+		p->atime.gran_exponent = exponent;
+		p->mtime.gran_exponent = exponent;
+		p->ctime.gran_exponent = exponent;
+		p->btime.gran_exponent = exponent;
+	}
+
+	return sizeof(*p);
+}
+EXPORT_SYMBOL(fsinfo_generic_timestamp_info);
+
+static int fsinfo_generic_volume_uuid(struct path *path, struct fsinfo_context *ctx)
+{
+	struct fsinfo_volume_uuid *p = ctx->buffer;
+	struct super_block *sb = path->dentry->d_sb;
+
+	memcpy(p, &sb->s_uuid, sizeof(*p));
+	return sizeof(*p);
+}
+
+static int fsinfo_generic_volume_id(struct path *path, struct fsinfo_context *ctx)
+{
+	return fsinfo_string(path->dentry->d_sb->s_id, ctx);
+}
+
+static const struct fsinfo_attribute fsinfo_common_attributes[] = {
+	FSINFO_VSTRUCT	(FSINFO_ATTR_STATFS,		fsinfo_generic_statfs),
+	FSINFO_VSTRUCT	(FSINFO_ATTR_IDS,		fsinfo_generic_ids),
+	FSINFO_VSTRUCT	(FSINFO_ATTR_LIMITS,		fsinfo_generic_limits),
+	FSINFO_VSTRUCT	(FSINFO_ATTR_SUPPORTS,		fsinfo_generic_supports),
+	FSINFO_VSTRUCT	(FSINFO_ATTR_TIMESTAMP_INFO,	fsinfo_generic_timestamp_info),
+	FSINFO_STRING	(FSINFO_ATTR_VOLUME_ID,		fsinfo_generic_volume_id),
+	FSINFO_VSTRUCT	(FSINFO_ATTR_VOLUME_UUID,	fsinfo_generic_volume_uuid),
+
+	FSINFO_LIST	(FSINFO_ATTR_FSINFO_ATTRIBUTES,	(void *)123UL),
+	FSINFO_VSTRUCT_N(FSINFO_ATTR_FSINFO_ATTRIBUTE_INFO, (void *)123UL),
+	{}
+};
+
+/*
+ * Determine an attribute's minimum buffer size and, if the buffer is large
+ * enough, get the attribute value.
+ */
+static int fsinfo_get_this_attribute(struct path *path,
+				     struct fsinfo_context *ctx,
+				     const struct fsinfo_attribute *attr)
+{
+	int buf_size;
+
+	if (ctx->Nth != 0 && !(attr->flags & (FSINFO_FLAGS_N | FSINFO_FLAGS_NM)))
+		return -ENODATA;
+	if (ctx->Mth != 0 && !(attr->flags & FSINFO_FLAGS_NM))
+		return -ENODATA;
+
+	switch (attr->type) {
+	case FSINFO_TYPE_VSTRUCT:
+		ctx->clear_tail = true;
+		buf_size = attr->size;
+		break;
+	case FSINFO_TYPE_STRING:
+	case FSINFO_TYPE_OPAQUE:
+	case FSINFO_TYPE_LIST:
+		buf_size = 4096;
+		break;
+	default:
+		return -ENOPKG;
+	}
+
+	if (ctx->buf_size < buf_size)
+		return buf_size;
+
+	return attr->get(path, ctx);
+}
+
+static void fsinfo_attributes_insert(struct fsinfo_context *ctx,
+				     const struct fsinfo_attribute *attr)
+{
+	__u32 *p = ctx->buffer;
+	unsigned int i;
+
+	if (ctx->usage >= ctx->buf_size ||
+	    ctx->buf_size - ctx->usage < sizeof(__u32)) {
+		ctx->usage += sizeof(__u32);
+		return;
+	}
+
+	for (i = 0; i < ctx->usage / sizeof(__u32); i++)
+		if (p[i] == attr->attr_id)
+			return;
+
+	p[i] = attr->attr_id;
+	ctx->usage += sizeof(__u32);
+}
+
+static int fsinfo_list_attributes(struct path *path,
+				  struct fsinfo_context *ctx,
+				  const struct fsinfo_attribute *attributes)
+{
+	const struct fsinfo_attribute *a;
+
+	for (a = attributes; a->get; a++)
+		fsinfo_attributes_insert(ctx, a);
+	return -EOPNOTSUPP; /* We want to go through all the lists */
+}
+
+static int fsinfo_get_attribute_info(struct path *path,
+				     struct fsinfo_context *ctx,
+				     const struct fsinfo_attribute *attributes)
+{
+	const struct fsinfo_attribute *a;
+	struct fsinfo_attribute_info *p = ctx->buffer;
+
+	if (!ctx->buf_size)
+		return sizeof(*p);
+
+	for (a = attributes; a->get; a++) {
+		if (a->attr_id == ctx->Nth) {
+			p->attr_id	= a->attr_id;
+			p->type		= a->type;
+			p->flags	= a->flags;
+			p->size		= a->size;
+			p->size		= a->size;
+			return sizeof(*p);
+		}
+	}
+	return -EOPNOTSUPP; /* We want to go through all the lists */
+}
+
+/**
+ * fsinfo_get_attribute - Look up and handle an attribute
+ * @path: The object to query
+ * @params: Parameters to define a request and place to store result
+ * @attributes: List of attributes to search.
+ *
+ * Look through a list of attributes for one that matches the requested
+ * attribute then call the handler for it.
+ */
+int fsinfo_get_attribute(struct path *path, struct fsinfo_context *ctx,
+			 const struct fsinfo_attribute *attributes)
+{
+	const struct fsinfo_attribute *a;
+
+	switch (ctx->requested_attr) {
+	case FSINFO_ATTR_FSINFO_ATTRIBUTE_INFO:
+		return fsinfo_get_attribute_info(path, ctx, attributes);
+	case FSINFO_ATTR_FSINFO_ATTRIBUTES:
+		return fsinfo_list_attributes(path, ctx, attributes);
+	default:
+		for (a = attributes; a->get; a++)
+			if (a->attr_id == ctx->requested_attr)
+				return fsinfo_get_this_attribute(path, ctx, a);
+		return -EOPNOTSUPP;
+	}
+}
+EXPORT_SYMBOL(fsinfo_get_attribute);
+
+/**
+ * generic_fsinfo - Handle an fsinfo attribute generically
+ * @path: The object to query
+ * @params: Parameters to define a request and place to store result
+ */
+static int fsinfo_call(struct path *path, struct fsinfo_context *ctx)
+{
+	int ret;
+
+	if (path->dentry->d_sb->s_op->fsinfo) {
+		ret = path->dentry->d_sb->s_op->fsinfo(path, ctx);
+		if (ret != -EOPNOTSUPP)
+			return ret;
+	}
+	ret = fsinfo_get_attribute(path, ctx, fsinfo_common_attributes);
+	if (ret != -EOPNOTSUPP)
+		return ret;
+
+	switch (ctx->requested_attr) {
+	case FSINFO_ATTR_FSINFO_ATTRIBUTE_INFO:
+		return -ENODATA;
+	case FSINFO_ATTR_FSINFO_ATTRIBUTES:
+		return ctx->usage;
+	default:
+		return -EOPNOTSUPP;
+	}
+}
+
+/**
+ * vfs_fsinfo - Retrieve filesystem information
+ * @path: The object to query
+ * @params: Parameters to define a request and place to store result
+ *
+ * Get an attribute on a filesystem or an object within a filesystem.  The
+ * filesystem attribute to be queried is indicated by @ctx->requested_attr, and
+ * if it's a multi-valued attribute, the particular value is selected by
+ * @ctx->Nth and then @ctx->Mth.
+ *
+ * For common attributes, a value may be fabricated if it is not supported by
+ * the filesystem.
+ *
+ * On success, the size of the attribute's value is returned (0 is a valid
+ * size).  A buffer will have been allocated and will be pointed to by
+ * @ctx->buffer.  The caller must free this with kvfree().
+ *
+ * Errors can also be returned: -ENOMEM if a buffer cannot be allocated, -EPERM
+ * or -EACCES if permission is denied by the LSM, -EOPNOTSUPP if an attribute
+ * doesn't exist for the specified object or -ENODATA if the attribute exists,
+ * but the Nth,Mth value does not exist.  -EMSGSIZE indicates that the value is
+ * unmanageable internally and -ENOPKG indicates other internal failure.
+ *
+ * Errors such as -EIO may also come from attempts to access media or servers
+ * to obtain the requested information if it's not immediately to hand.
+ *
+ * [*] Note that the caller may set @ctx->want_size_only if it only wants the
+ *     size of the value and not the data.  If this is set, a buffer may not be
+ *     allocated under some circumstances.  This is intended for size query by
+ *     userspace.
+ *
+ * [*] Note that @ctx->clear_tail will be returned set if the data should be
+ *     padded out with zeros when writing it to userspace.
+ */
+static int vfs_fsinfo(struct path *path, struct fsinfo_context *ctx)
+{
+	struct dentry *dentry = path->dentry;
+	int ret;
+
+	ret = security_sb_statfs(dentry);
+	if (ret)
+		return ret;
+
+	/* Call the handler to find out the buffer size required. */
+	ctx->buf_size = 0;
+	ret = fsinfo_call(path, ctx);
+	if (ret < 0 || ctx->want_size_only)
+		return ret;
+	ctx->buf_size = ret;
+
+	do {
+		/* Allocate a buffer of the requested size. */
+		if (ctx->buf_size > INT_MAX)
+			return -EMSGSIZE;
+		ctx->buffer = kvzalloc(ctx->buf_size, GFP_KERNEL);
+		if (!ctx->buffer)
+			return -ENOMEM;
+
+		ctx->usage = 0;
+		ctx->skip = 0;
+		ret = fsinfo_call(path, ctx);
+		if (IS_ERR_VALUE((long)ret))
+			return ret;
+		if ((unsigned int)ret <= ctx->buf_size)
+			return ret; /* It fitted */
+
+		/* We need to resize the buffer */
+		ctx->buf_size = roundup(ret, PAGE_SIZE);
+		kvfree(ctx->buffer);
+		ctx->buffer = NULL;
+	} while (!signal_pending(current));
+
+	return -ERESTARTSYS;
+}
+
+static int vfs_fsinfo_path(int dfd, const char __user *pathname,
+			   const struct fsinfo_params *up,
+			   struct fsinfo_context *ctx)
+{
+	struct path path;
+	unsigned lookup_flags = LOOKUP_FOLLOW | LOOKUP_AUTOMOUNT;
+	int ret = -EINVAL;
+
+	if (up->resolve_flags & ~VALID_RESOLVE_FLAGS)
+		return -EINVAL;
+	if (up->at_flags & ~(AT_SYMLINK_NOFOLLOW | AT_NO_AUTOMOUNT |
+			     AT_EMPTY_PATH))
+		return -EINVAL;
+
+	if (up->resolve_flags & RESOLVE_NO_XDEV)
+		lookup_flags |= LOOKUP_NO_XDEV;
+	if (up->resolve_flags & RESOLVE_NO_MAGICLINKS)
+		lookup_flags |= LOOKUP_NO_MAGICLINKS;
+	if (up->resolve_flags & RESOLVE_NO_SYMLINKS)
+		lookup_flags |= LOOKUP_NO_SYMLINKS;
+	if (up->resolve_flags & RESOLVE_BENEATH)
+		lookup_flags |= LOOKUP_BENEATH;
+	if (up->resolve_flags & RESOLVE_IN_ROOT)
+		lookup_flags |= LOOKUP_IN_ROOT;
+	if (up->at_flags & AT_SYMLINK_NOFOLLOW)
+		lookup_flags &= ~LOOKUP_FOLLOW;
+	if (up->at_flags & AT_NO_AUTOMOUNT)
+		lookup_flags &= ~LOOKUP_AUTOMOUNT;
+	if (up->at_flags & AT_EMPTY_PATH)
+		lookup_flags |= LOOKUP_EMPTY;
+
+retry:
+	ret = user_path_at(dfd, pathname, lookup_flags, &path);
+	if (ret)
+		goto out;
+
+	ret = vfs_fsinfo(&path, ctx);
+	path_put(&path);
+	if (retry_estale(ret, lookup_flags)) {
+		lookup_flags |= LOOKUP_REVAL;
+		goto retry;
+	}
+out:
+	return ret;
+}
+
+static int vfs_fsinfo_fd(unsigned int fd, struct fsinfo_context *ctx)
+{
+	struct fd f = fdget_raw(fd);
+	int ret = -EBADF;
+
+	if (f.file) {
+		ret = vfs_fsinfo(&f.file->f_path, ctx);
+		fdput(f);
+	}
+	return ret;
+}
+
+/**
+ * sys_fsinfo - System call to get filesystem information
+ * @dfd: Base directory to pathwalk from or fd referring to filesystem.
+ * @pathname: Filesystem to query or NULL.
+ * @params: Parameters to define request (NULL: FSINFO_ATTR_STATFS).
+ * @params_size: Size of parameter buffer.
+ * @result_buffer: Result buffer.
+ * @result_buf_size: Size of result buffer.
+ *
+ * Get information on a filesystem.  The filesystem attribute to be queried is
+ * indicated by @_params->request, and some of the attributes can have multiple
+ * values, indexed by @_params->Nth and @_params->Mth.  If @_params is NULL,
+ * then the 0th fsinfo_attr_statfs attribute is queried.  If an attribute does
+ * not exist, EOPNOTSUPP is returned; if the Nth,Mth value does not exist,
+ * ENODATA is returned.
+ *
+ * On success, the size of the attribute's value is returned.  If
+ * @result_buf_size is 0 or @result_buffer is NULL, only the size is returned.
+ * If the size of the value is larger than @result_buf_size, it will be
+ * truncated by the copy.  If the size of the value is smaller than
+ * @result_buf_size then the excess buffer space will be cleared.  The full
+ * size of the value will be returned, irrespective of how much data is
+ * actually placed in the buffer.
+ */
+SYSCALL_DEFINE6(fsinfo,
+		int, dfd,
+		const char __user *, pathname,
+		const struct fsinfo_params __user *, params,
+		size_t, params_size,
+		void __user *, result_buffer,
+		size_t, result_buf_size)
+{
+	struct fsinfo_context ctx;
+	struct fsinfo_params user_params;
+	unsigned int result_size;
+	void *r;
+	int ret;
+
+	if ((!params &&  params_size) ||
+	    ( params && !params_size) ||
+	    (!result_buffer &&  result_buf_size) ||
+	    ( result_buffer && !result_buf_size))
+		return -EINVAL;
+	if (result_buf_size > UINT_MAX)
+		return -EOVERFLOW;
+
+	memset(&ctx, 0, sizeof(ctx));
+	ctx.requested_attr	= FSINFO_ATTR_STATFS;
+	ctx.flags		= FSINFO_FLAGS_QUERY_PATH;
+	ctx.want_size_only	= (result_buf_size == 0);
+
+	if (params) {
+		ret = copy_struct_from_user(&user_params, sizeof(user_params),
+					    params, params_size);
+		if (ret < 0)
+			return ret;
+		if (user_params.flags & ~FSINFO_FLAGS_QUERY_MASK)
+			return -EINVAL;
+		ctx.flags = user_params.flags;
+		ctx.requested_attr = user_params.request;
+		ctx.Nth = user_params.Nth;
+		ctx.Mth = user_params.Mth;
+	}
+
+	switch (ctx.flags & FSINFO_FLAGS_QUERY_MASK) {
+	case FSINFO_FLAGS_QUERY_PATH:
+		ret = vfs_fsinfo_path(dfd, pathname, &user_params, &ctx);
+		break;
+	case FSINFO_FLAGS_QUERY_FD:
+		if (pathname)
+			return -EINVAL;
+		ret = vfs_fsinfo_fd(dfd, &ctx);
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	if (ret < 0)
+		goto error;
+
+	r = ctx.buffer + ctx.skip;
+	result_size = min_t(size_t, ret, result_buf_size);
+	if (result_size > 0 &&
+	    copy_to_user(result_buffer, r, result_size) != 0) {
+		ret = -EFAULT;
+		goto error;
+	}
+
+	/* Clear any part of the buffer that we won't fill if we're putting a
+	 * struct in there.  Strings, opaque objects and arrays are expected to
+	 * be variable length.
+	 */
+	if (ctx.clear_tail &&
+	    result_buf_size > result_size &&
+	    clear_user(result_buffer + result_size,
+		       result_buf_size - result_size) != 0) {
+		ret = -EFAULT;
+		goto error;
+	}
+
+error:
+	kvfree(ctx.buffer);
+	return ret;
+}
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 28a29356eace..3284f497de0a 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -68,6 +68,7 @@  struct fsverity_info;
 struct fsverity_operations;
 struct fs_context;
 struct fs_parameter_spec;
+struct fsinfo_context;
 
 extern void __init inode_init(void);
 extern void __init inode_init_early(void);
@@ -1963,6 +1964,9 @@  struct super_operations {
 	int (*thaw_super) (struct super_block *);
 	int (*unfreeze_fs) (struct super_block *);
 	int (*statfs) (struct dentry *, struct kstatfs *);
+#ifdef CONFIG_FSINFO
+	int (*fsinfo)(struct path *, struct fsinfo_context *);
+#endif
 	int (*remount_fs) (struct super_block *, int *, char *);
 	void (*umount_begin) (struct super_block *);
 
diff --git a/include/linux/fsinfo.h b/include/linux/fsinfo.h
new file mode 100644
index 000000000000..a811d69b02ff
--- /dev/null
+++ b/include/linux/fsinfo.h
@@ -0,0 +1,74 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/* Filesystem information query
+ *
+ * Copyright (C) 2020 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells ([e-mail])
+ */
+
+#ifndef _LINUX_FSINFO_H
+#define _LINUX_FSINFO_H
+
+#ifdef CONFIG_FSINFO
+
+#include <uapi/linux/fsinfo.h>
+
+struct path;
+
+#define FSINFO_NORMAL_ATTR_MAX_SIZE 4096
+
+struct fsinfo_context {
+	__u32		flags;		/* [in] FSINFO_FLAGS_* */
+	__u32		requested_attr;	/* [in] What is being asking for */
+	__u32		Nth;		/* [in] Instance of it (some may have multiple) */
+	__u32		Mth;		/* [in] Subinstance */
+	bool		want_size_only;	/* [in] Just want to know the size, not the data */
+	bool		clear_tail;	/* [out] T if tail of buffer should be cleared */
+	unsigned int	skip;		/* [out] Number of bytes to skip in buffer */
+	unsigned int	usage;		/* [tmp] Amount of buffer used (if large) */
+	unsigned int	buf_size;	/* [tmp] Size of ->buffer[] */
+	void		*buffer;	/* [out] The reply buffer */
+};
+
+/*
+ * A filesystem information attribute definition.
+ */
+struct fsinfo_attribute {
+	unsigned int		attr_id;	/* The ID of the attribute */
+	enum fsinfo_value_type	type:8;		/* The type of the attribute's value(s) */
+	unsigned int		flags:8;
+	unsigned int		size:16;	/* - Value size (FSINFO_STRUCT/LIST) */
+	int (*get)(struct path *path, struct fsinfo_context *params);
+};
+
+#define __FSINFO(A, T, S, G, F) \
+	{ .attr_id = A, .type = T, .flags = F, .size = S, .get = G }
+
+#define _FSINFO(A, T, S, G)	__FSINFO(A, T, S, G, 0)
+#define _FSINFO_N(A, T, S, G)	__FSINFO(A, T, S, G, FSINFO_FLAGS_N)
+#define _FSINFO_NM(A, T, S, G)	__FSINFO(A, T, S, G, FSINFO_FLAGS_NM)
+
+#define _FSINFO_VSTRUCT(A,S,G)	  _FSINFO   (A, FSINFO_TYPE_VSTRUCT, sizeof(S), G)
+#define _FSINFO_VSTRUCT_N(A,S,G)  _FSINFO_N (A, FSINFO_TYPE_VSTRUCT, sizeof(S), G)
+#define _FSINFO_VSTRUCT_NM(A,S,G) _FSINFO_NM(A, FSINFO_TYPE_VSTRUCT, sizeof(S), G)
+
+#define FSINFO_VSTRUCT(A,G)	_FSINFO_VSTRUCT   (A, A##__STRUCT, G)
+#define FSINFO_VSTRUCT_N(A,G)	_FSINFO_VSTRUCT_N (A, A##__STRUCT, G)
+#define FSINFO_VSTRUCT_NM(A,G)	_FSINFO_VSTRUCT_NM(A, A##__STRUCT, G)
+#define FSINFO_STRING(A,G)	_FSINFO   (A, FSINFO_TYPE_STRING, 0, G)
+#define FSINFO_STRING_N(A,G)	_FSINFO_N (A, FSINFO_TYPE_STRING, 0, G)
+#define FSINFO_STRING_NM(A,G)	_FSINFO_NM(A, FSINFO_TYPE_STRING, 0, G)
+#define FSINFO_OPAQUE(A,G)	_FSINFO   (A, FSINFO_TYPE_OPAQUE, 0, G)
+#define FSINFO_LIST(A,G)	_FSINFO   (A, FSINFO_TYPE_LIST, sizeof(A##__STRUCT), G)
+#define FSINFO_LIST_N(A,G)	_FSINFO_N (A, FSINFO_TYPE_LIST, sizeof(A##__STRUCT), G)
+
+extern int fsinfo_opaque(const void *, struct fsinfo_context *, unsigned int);
+extern int fsinfo_string(const char *, struct fsinfo_context *);
+extern int fsinfo_generic_timestamp_info(struct path *, struct fsinfo_context *);
+extern int fsinfo_generic_supports(struct path *, struct fsinfo_context *);
+extern int fsinfo_generic_limits(struct path *, struct fsinfo_context *);
+extern int fsinfo_get_attribute(struct path *, struct fsinfo_context *,
+				const struct fsinfo_attribute *);
+
+#endif /* CONFIG_FSINFO */
+
+#endif /* _LINUX_FSINFO_H */
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 88d03fd627ab..e31ad49af4c3 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -47,6 +47,7 @@  struct stat64;
 struct statfs;
 struct statfs64;
 struct statx;
+struct fsinfo_params;
 struct __sysctl_args;
 struct sysinfo;
 struct timespec;
@@ -1007,6 +1008,9 @@  asmlinkage long sys_pidfd_send_signal(int pidfd, int sig,
 asmlinkage long sys_pidfd_getfd(int pidfd, int fd, unsigned int flags);
 asmlinkage long sys_watch_mount(int dfd, const char __user *path,
 				unsigned int at_flags, int watch_fd, int watch_id);
+asmlinkage long sys_fsinfo(int dfd, const char __user *pathname,
+			   const struct fsinfo_params __user *params, size_t params_size,
+			   void __user *result_buffer, size_t result_buf_size);
 
 /*
  * Architecture-specific system calls
diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
index fcdca8c7d30a..9e38f611ab56 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@ -859,9 +859,11 @@  __SYSCALL(__NR_pidfd_getfd, sys_pidfd_getfd)
 __SYSCALL(__NR_faccessat2, sys_faccessat2)
 #define __NR_watch_mount 440
 __SYSCALL(__NR_watch_mount, sys_watch_mount)
+#define __NR_fsinfo 441
+__SYSCALL(__NR_fsinfo, sys_fsinfo)
 
 #undef __NR_syscalls
-#define __NR_syscalls 441
+#define __NR_syscalls 442
 
 /*
  * 32 bit systems traditionally used different
diff --git a/include/uapi/linux/fsinfo.h b/include/uapi/linux/fsinfo.h
new file mode 100644
index 000000000000..65892239ba86
--- /dev/null
+++ b/include/uapi/linux/fsinfo.h
@@ -0,0 +1,189 @@ 
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/* fsinfo() definitions.
+ *
+ * Copyright (C) 2020 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells ([e-mail])
+ */
+#ifndef _UAPI_LINUX_FSINFO_H
+#define _UAPI_LINUX_FSINFO_H
+
+#include <linux/types.h>
+#include <linux/socket.h>
+#include <linux/openat2.h>
+
+/*
+ * The filesystem attributes that can be requested.  Note that some attributes
+ * may have multiple instances which can be switched in the parameter block.
+ */
+#define FSINFO_ATTR_STATFS		0x00	/* statfs()-style state */
+#define FSINFO_ATTR_IDS			0x01	/* Filesystem IDs */
+#define FSINFO_ATTR_LIMITS		0x02	/* Filesystem limits */
+#define FSINFO_ATTR_SUPPORTS		0x03	/* What's supported in statx, iocflags, ... */
+#define FSINFO_ATTR_TIMESTAMP_INFO	0x04	/* Inode timestamp info */
+#define FSINFO_ATTR_VOLUME_ID		0x05	/* Volume ID (string) */
+#define FSINFO_ATTR_VOLUME_UUID		0x06	/* Volume UUID (LE uuid) */
+#define FSINFO_ATTR_VOLUME_NAME		0x07	/* Volume name (string) */
+
+#define FSINFO_ATTR_FSINFO_ATTRIBUTE_INFO 0x100	/* Information about attr N (for path) */
+#define FSINFO_ATTR_FSINFO_ATTRIBUTES	0x101	/* List of supported attrs (for path) */
+
+/*
+ * Optional fsinfo() parameter structure.
+ *
+ * If this is not given, it is assumed that fsinfo_attr_statfs instance 0,0 is
+ * desired.
+ */
+struct fsinfo_params {
+	__u64	resolve_flags;	/* RESOLVE_* flags */
+	__u32	at_flags;	/* AT_* flags */
+	__u32	flags;		/* Flags controlling fsinfo() specifically */
+#define FSINFO_FLAGS_QUERY_MASK	0x0007 /* What object should fsinfo() query? */
+#define FSINFO_FLAGS_QUERY_PATH	0x0000 /* - path, specified by dirfd,pathname,AT_EMPTY_PATH */
+#define FSINFO_FLAGS_QUERY_FD	0x0001 /* - fd specified by dirfd */
+	__u32	request;	/* ID of requested attribute */
+	__u32	Nth;		/* Instance of it (some may have multiple) */
+	__u32	Mth;		/* Subinstance of Nth instance */
+};
+
+enum fsinfo_value_type {
+	FSINFO_TYPE_VSTRUCT	= 0,	/* Version-lengthed struct (up to 4096 bytes) */
+	FSINFO_TYPE_STRING	= 1,	/* NUL-term var-length string (up to 4095 chars) */
+	FSINFO_TYPE_OPAQUE	= 2,	/* Opaque blob (unlimited size) */
+	FSINFO_TYPE_LIST	= 3,	/* List of ints/structs (unlimited size) */
+};
+
+/*
+ * Information struct for fsinfo(FSINFO_ATTR_FSINFO_ATTRIBUTE_INFO).
+ *
+ * This gives information about the attributes supported by fsinfo for the
+ * given path.
+ */
+struct fsinfo_attribute_info {
+	unsigned int		attr_id;	/* The ID of the attribute */
+	enum fsinfo_value_type	type;		/* The type of the attribute's value(s) */
+	unsigned int		flags;
+#define FSINFO_FLAGS_N		0x01		/* - Attr has a set of values */
+#define FSINFO_FLAGS_NM		0x02		/* - Attr has a set of sets of values */
+	unsigned int		size;		/* - Value size (FSINFO_STRUCT/FSINFO_LIST) */
+};
+
+#define FSINFO_ATTR_FSINFO_ATTRIBUTE_INFO__STRUCT struct fsinfo_attribute_info
+#define FSINFO_ATTR_FSINFO_ATTRIBUTES__STRUCT __u32
+
+struct fsinfo_u128 {
+#if defined(__BYTE_ORDER) ? __BYTE_ORDER == __BIG_ENDIAN : defined(__BIG_ENDIAN)
+	__u64	hi;
+	__u64	lo;
+#elif defined(__BYTE_ORDER) ? __BYTE_ORDER == __LITTLE_ENDIAN : defined(__LITTLE_ENDIAN)
+	__u64	lo;
+	__u64	hi;
+#endif
+};
+
+/*
+ * Information struct for fsinfo(FSINFO_ATTR_STATFS).
+ * - This gives extended filesystem information.
+ */
+struct fsinfo_statfs {
+	struct fsinfo_u128 f_blocks;	/* Total number of blocks in fs */
+	struct fsinfo_u128 f_bfree;	/* Total number of free blocks */
+	struct fsinfo_u128 f_bavail;	/* Number of free blocks available to ordinary user */
+	struct fsinfo_u128 f_files;	/* Total number of file nodes in fs */
+	struct fsinfo_u128 f_ffree;	/* Number of free file nodes */
+	struct fsinfo_u128 f_favail;	/* Number of file nodes available to ordinary user */
+	__u64	f_bsize;		/* Optimal block size */
+	__u64	f_frsize;		/* Fragment size */
+};
+
+#define FSINFO_ATTR_STATFS__STRUCT struct fsinfo_statfs
+
+/*
+ * Information struct for fsinfo(FSINFO_ATTR_IDS).
+ *
+ * List of basic identifiers as is normally found in statfs().
+ */
+struct fsinfo_ids {
+	char	f_fs_name[15 + 1];	/* Filesystem name */
+	__u64	f_fsid;			/* Short 64-bit Filesystem ID (as statfs) */
+	__u64	f_sb_id;		/* Internal superblock ID for sbnotify()/mntnotify() */
+	__u32	f_fstype;		/* Filesystem type from linux/magic.h [uncond] */
+	__u32	f_dev_major;		/* As st_dev_* from struct statx [uncond] */
+	__u32	f_dev_minor;
+	__u32	__padding[1];
+};
+
+#define FSINFO_ATTR_IDS__STRUCT struct fsinfo_ids
+
+/*
+ * Information struct for fsinfo(FSINFO_ATTR_LIMITS).
+ *
+ * List of supported filesystem limits.
+ */
+struct fsinfo_limits {
+	struct fsinfo_u128 max_file_size;	/* Maximum file size */
+	struct fsinfo_u128 max_ino;		/* Maximum inode number */
+	__u64	max_uid;			/* Maximum UID supported */
+	__u64	max_gid;			/* Maximum GID supported */
+	__u64	max_projid;			/* Maximum project ID supported */
+	__u64	max_hard_links;			/* Maximum number of hard links on a file */
+	__u64	max_xattr_body_len;		/* Maximum xattr content length */
+	__u32	max_xattr_name_len;		/* Maximum xattr name length */
+	__u32	max_filename_len;		/* Maximum filename length */
+	__u32	max_symlink_len;		/* Maximum symlink content length */
+	__u32	max_dev_major;			/* Maximum device major representable */
+	__u32	max_dev_minor;			/* Maximum device minor representable */
+	__u32	__padding[1];
+};
+
+#define FSINFO_ATTR_LIMITS__STRUCT struct fsinfo_limits
+
+/*
+ * Information struct for fsinfo(FSINFO_ATTR_SUPPORTS).
+ *
+ * What's supported in various masks, such as statx() attribute and mask bits
+ * and IOC flags.
+ */
+struct fsinfo_supports {
+	__u64	stx_attributes;		/* What statx::stx_attributes are supported */
+	__u32	stx_mask;		/* What statx::stx_mask bits are supported */
+	__u32	fs_ioc_getflags;	/* What FS_IOC_GETFLAGS may return */
+	__u32	fs_ioc_setflags_set;	/* What FS_IOC_SETFLAGS may set */
+	__u32	fs_ioc_setflags_clear;	/* What FS_IOC_SETFLAGS may clear */
+	__u32	fs_ioc_fsgetxattr_xflags; /* What FS_IOC_FSGETXATTR[A] may return in fsx_xflags */
+	__u32	fs_ioc_fssetxattr_xflags_set; /* What FS_IOC_FSSETXATTR may set in fsx_xflags */
+	__u32	fs_ioc_fssetxattr_xflags_clear; /* What FS_IOC_FSSETXATTR may set in fsx_xflags */
+	__u32	win_file_attrs;		/* What DOS/Windows FILE_* attributes are supported */
+};
+
+#define FSINFO_ATTR_SUPPORTS__STRUCT struct fsinfo_supports
+
+struct fsinfo_timestamp_one {
+	__s64	minimum;	/* Minimum timestamp value in seconds */
+	__s64	maximum;	/* Maximum timestamp value in seconds */
+	__u16	gran_mantissa;	/* Granularity(secs) = mant * 10^exp */
+	__s8	gran_exponent;
+	__u8	__padding[5];
+};
+
+/*
+ * Information struct for fsinfo(FSINFO_ATTR_TIMESTAMP_INFO).
+ */
+struct fsinfo_timestamp_info {
+	struct fsinfo_timestamp_one	atime;	/* Access time */
+	struct fsinfo_timestamp_one	mtime;	/* Modification time */
+	struct fsinfo_timestamp_one	ctime;	/* Change time */
+	struct fsinfo_timestamp_one	btime;	/* Birth/creation time */
+};
+
+#define FSINFO_ATTR_TIMESTAMP_INFO__STRUCT struct fsinfo_timestamp_info
+
+/*
+ * Information struct for fsinfo(FSINFO_ATTR_VOLUME_UUID).
+ */
+struct fsinfo_volume_uuid {
+	__u8	uuid[16];
+};
+
+#define FSINFO_ATTR_VOLUME_UUID__STRUCT struct fsinfo_volume_uuid
+
+#endif /* _UAPI_LINUX_FSINFO_H */
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index 3e1c5c9d2efe..f72a9e4ddc9a 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -51,6 +51,7 @@  COND_SYSCALL_COMPAT(io_pgetevents);
 COND_SYSCALL(io_uring_setup);
 COND_SYSCALL(io_uring_enter);
 COND_SYSCALL(io_uring_register);
+COND_SYSCALL(fsinfo);
 
 /* fs/xattr.c */
 
diff --git a/samples/vfs/Makefile b/samples/vfs/Makefile
index 00b6824f9237..d63af5106fc2 100644
--- a/samples/vfs/Makefile
+++ b/samples/vfs/Makefile
@@ -1,5 +1,5 @@ 
 # SPDX-License-Identifier: GPL-2.0-only
-userprogs := test-fsmount test-statx
+userprogs := test-fsinfo test-fsmount test-statx
 always-y := $(userprogs)
 
 userccflags += -I usr/include
diff --git a/samples/vfs/test-fsinfo.c b/samples/vfs/test-fsinfo.c
new file mode 100644
index 000000000000..934b25399ffe
--- /dev/null
+++ b/samples/vfs/test-fsinfo.c
@@ -0,0 +1,646 @@ 
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Test the fsinfo() system call
+ *
+ * Copyright (C) 2020 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells ([e-mail])
+ */
+
+#define _GNU_SOURCE
+#define _ATFILE_SOURCE
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+#include <unistd.h>
+#include <ctype.h>
+#include <errno.h>
+#include <time.h>
+#include <math.h>
+#include <fcntl.h>
+#include <sys/syscall.h>
+#include <linux/fsinfo.h>
+#include <linux/socket.h>
+#include <sys/stat.h>
+#include <arpa/inet.h>
+
+#ifndef __NR_fsinfo
+#define __NR_fsinfo -1
+#endif
+
+static bool debug = 0;
+static bool list_last;
+
+static __attribute__((unused))
+ssize_t fsinfo(int dfd, const char *filename,
+	       struct fsinfo_params *params, size_t params_size,
+	       void *result_buffer, size_t result_buf_size)
+{
+	return syscall(__NR_fsinfo, dfd, filename,
+		       params, params_size,
+		       result_buffer, result_buf_size);
+}
+
+struct fsinfo_attribute {
+	unsigned int		attr_id;
+	enum fsinfo_value_type	type;
+	unsigned int		size;
+	const char		*name;
+	void (*dump)(void *reply, unsigned int size);
+};
+
+static const struct fsinfo_attribute fsinfo_attributes[];
+
+static ssize_t get_fsinfo(const char *, const char *, struct fsinfo_params *, void **);
+
+static void dump_hex(FILE *f, unsigned char *data, int from, int to)
+{
+	unsigned offset, col = 0;
+	bool print_offset = true;
+
+	for (offset = from; offset < to; offset++) {
+		if (print_offset) {
+			fprintf(f, "%04x: ", offset);
+			print_offset = 0;
+		}
+		fprintf(f, "%02x", data[offset]);
+		col++;
+		if ((col & 3) == 0) {
+			if ((col & 15) == 0) {
+				fprintf(f, "\n");
+				print_offset = 1;
+			} else {
+				fprintf(f, " ");
+			}
+		}
+	}
+
+	if (!print_offset)
+		fprintf(f, "\n");
+}
+
+static void dump_attribute_info(void *reply, unsigned int size)
+{
+	struct fsinfo_attribute_info *attr_info = reply;
+	const struct fsinfo_attribute *attr;
+	char type[32], val_size[32];
+
+	switch (attr_info->type) {
+	case FSINFO_TYPE_VSTRUCT:	strcpy(type, "V-STRUCT");	break;
+	case FSINFO_TYPE_STRING:	strcpy(type, "STRING");		break;
+	case FSINFO_TYPE_OPAQUE:	strcpy(type, "OPAQUE");		break;
+	case FSINFO_TYPE_LIST:		strcpy(type, "LIST");		break;
+	default:
+		sprintf(type, "type-%x", attr_info->type);
+		break;
+	}
+
+	if (attr_info->flags & FSINFO_FLAGS_N)
+		strcat(type, " x N");
+	else if (attr_info->flags & FSINFO_FLAGS_NM)
+		strcat(type, " x NM");
+
+	for (attr = fsinfo_attributes; attr->name; attr++)
+		if (attr->attr_id == attr_info->attr_id)
+			break;
+
+	if (attr_info->size)
+		sprintf(val_size, "%u", attr_info->size);
+	else
+		strcpy(val_size, "-");
+
+	printf("%8x %-12s %08x %5s %s\n",
+	       attr_info->attr_id,
+	       type,
+	       attr_info->flags,
+	       val_size,
+	       attr->name ? attr->name : "");
+}
+
+static void dump_fsinfo_generic_statfs(void *reply, unsigned int size)
+{
+	struct fsinfo_statfs *f = reply;
+
+	printf("\n");
+	printf("\tblocks       : n=%llu fr=%llu av=%llu\n",
+	       (unsigned long long)f->f_blocks.lo,
+	       (unsigned long long)f->f_bfree.lo,
+	       (unsigned long long)f->f_bavail.lo);
+
+	printf("\tfiles        : n=%llu fr=%llu av=%llu\n",
+	       (unsigned long long)f->f_files.lo,
+	       (unsigned long long)f->f_ffree.lo,
+	       (unsigned long long)f->f_favail.lo);
+	printf("\tbsize        : %llu\n",
+	       (unsigned long long)f->f_bsize);
+	printf("\tfrsize       : %llu\n",
+	       (unsigned long long)f->f_frsize);
+}
+
+static void dump_fsinfo_generic_ids(void *reply, unsigned int size)
+{
+	struct fsinfo_ids *f = reply;
+
+	printf("\n");
+	printf("\tdev          : %02x:%02x\n", f->f_dev_major, f->f_dev_minor);
+	printf("\tfs           : type=%x name=%s\n", f->f_fstype, f->f_fs_name);
+	printf("\tfsid         : %llx\n", (unsigned long long)f->f_fsid);
+	printf("\tsbid         : %llx\n", (unsigned long long)f->f_sb_id);
+}
+
+static void dump_fsinfo_generic_limits(void *reply, unsigned int size)
+{
+	struct fsinfo_limits *f = reply;
+
+	printf("\n");
+	printf("\tmax file size: %llx%016llx\n",
+	       (unsigned long long)f->max_file_size.hi,
+	       (unsigned long long)f->max_file_size.lo);
+	printf("\tmax ino      : %llx%016llx\n",
+	       (unsigned long long)f->max_ino.hi,
+	       (unsigned long long)f->max_ino.lo);
+	printf("\tmax ids      : u=%llx g=%llx p=%llx\n",
+	       (unsigned long long)f->max_uid,
+	       (unsigned long long)f->max_gid,
+	       (unsigned long long)f->max_projid);
+	printf("\tmax dev      : maj=%x min=%x\n",
+	       f->max_dev_major, f->max_dev_minor);
+	printf("\tmax links    : %llx\n",
+	       (unsigned long long)f->max_hard_links);
+	printf("\tmax xattr    : n=%x b=%llx\n",
+	       f->max_xattr_name_len,
+	       (unsigned long long)f->max_xattr_body_len);
+	printf("\tmax len      : file=%x sym=%x\n",
+	       f->max_filename_len, f->max_symlink_len);
+}
+
+static void dump_fsinfo_generic_supports(void *reply, unsigned int size)
+{
+	struct fsinfo_supports *f = reply;
+
+	printf("\n");
+	printf("\tstx_attr     : %llx\n", (unsigned long long)f->stx_attributes);
+	printf("\tstx_mask     : %x\n", f->stx_mask);
+	printf("\tfs_ioc_*flags: get=%x set=%x clr=%x\n",
+	       f->fs_ioc_getflags, f->fs_ioc_setflags_set, f->fs_ioc_setflags_clear);
+	printf("\tfs_ioc_*xattr: fsx_xflags: get=%x set=%x clr=%x\n",
+	       f->fs_ioc_fsgetxattr_xflags,
+	       f->fs_ioc_fssetxattr_xflags_set,
+	       f->fs_ioc_fssetxattr_xflags_clear);
+	printf("\twin_fattrs   : %x\n", f->win_file_attrs);
+}
+
+static void print_time(struct fsinfo_timestamp_one *t, char stamp)
+{
+	printf("\t%ctime       : gran=%uE%d range=%llx-%llx\n",
+	       stamp,
+	       t->gran_mantissa, t->gran_exponent,
+	       (long long)t->minimum, (long long)t->maximum);
+}
+
+static void dump_fsinfo_generic_timestamp_info(void *reply, unsigned int size)
+{
+	struct fsinfo_timestamp_info *f = reply;
+
+	printf("\n");
+	print_time(&f->atime, 'a');
+	print_time(&f->mtime, 'm');
+	print_time(&f->ctime, 'c');
+	print_time(&f->btime, 'b');
+}
+
+static void dump_fsinfo_generic_volume_uuid(void *reply, unsigned int size)
+{
+	struct fsinfo_volume_uuid *f = reply;
+
+	printf("%02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x"
+	       "-%02x%02x%02x%02x%02x%02x\n",
+	       f->uuid[ 0], f->uuid[ 1],
+	       f->uuid[ 2], f->uuid[ 3],
+	       f->uuid[ 4], f->uuid[ 5],
+	       f->uuid[ 6], f->uuid[ 7],
+	       f->uuid[ 8], f->uuid[ 9],
+	       f->uuid[10], f->uuid[11],
+	       f->uuid[12], f->uuid[13],
+	       f->uuid[14], f->uuid[15]);
+}
+
+static void dump_string(void *reply, unsigned int size)
+{
+	char *s = reply, *p;
+	bool nl = false, last_nl = false;
+
+	p = s;
+	if (size >= 4096) {
+		size = 4096;
+		p[4092] = '.';
+		p[4093] = '.';
+		p[4094] = '.';
+		p[4095] = 0;
+	} else {
+		p[size] = 0;
+	}
+
+	for (p = s; *p; p++) {
+		if (*p == '\n') {
+			last_nl = nl = true;
+			continue;
+		}
+		last_nl = false;
+		if (!isprint(*p) && *p != '\t')
+			*p = '?';
+	}
+
+	if (nl)
+		putchar('\n');
+	printf("%s", s);
+	if (!last_nl)
+		putchar('\n');
+}
+
+#define dump_fsinfo_meta_attribute_info		(void *)0x123
+#define dump_fsinfo_meta_attributes		(void *)0x123
+
+/*
+ *
+ */
+#define __FSINFO(A, T, S, G, F, N)					\
+	{ .attr_id = A, .type = T, .size = S, .name = N, .dump = dump_##G }
+
+#define _FSINFO(A,T,S,G,N)	__FSINFO(A, T, S, G, 0, N)
+#define _FSINFO_N(A,T,S,G,N)	__FSINFO(A, T, S, G, FSINFO_FLAGS_N, N)
+#define _FSINFO_NM(A,T,S,G,N)	__FSINFO(A, T, S, G, FSINFO_FLAGS_NM, N)
+
+#define _FSINFO_VSTRUCT(A,S,G,N)    _FSINFO   (A, FSINFO_TYPE_VSTRUCT, sizeof(S), G, N)
+#define _FSINFO_VSTRUCT_N(A,S,G,N)  _FSINFO_N (A, FSINFO_TYPE_VSTRUCT, sizeof(S), G, N)
+#define _FSINFO_VSTRUCT_NM(A,S,G,N) _FSINFO_NM(A, FSINFO_TYPE_VSTRUCT, sizeof(S), G, N)
+
+#define FSINFO_VSTRUCT(A,G)	_FSINFO_VSTRUCT   (A, A##__STRUCT, G, #A)
+#define FSINFO_VSTRUCT_N(A,G)	_FSINFO_VSTRUCT_N (A, A##__STRUCT, G, #A)
+#define FSINFO_VSTRUCT_NM(A,G)	_FSINFO_VSTRUCT_NM(A, A##__STRUCT, G, #A)
+#define FSINFO_STRING(A,G)	_FSINFO   (A, FSINFO_TYPE_STRING, 0, G, #A)
+#define FSINFO_STRING_N(A,G)	_FSINFO_N (A, FSINFO_TYPE_STRING, 0, G, #A)
+#define FSINFO_STRING_NM(A,G)	_FSINFO_NM(A, FSINFO_TYPE_STRING, 0, G, #A)
+#define FSINFO_OPAQUE(A,G)	_FSINFO   (A, FSINFO_TYPE_OPAQUE, 0, G, #A)
+#define FSINFO_LIST(A,G)	_FSINFO   (A, FSINFO_TYPE_LIST, sizeof(A##__STRUCT), G, #A)
+#define FSINFO_LIST_N(A,G)	_FSINFO_N (A, FSINFO_TYPE_LIST, sizeof(A##__STRUCT), G, #A)
+
+static const struct fsinfo_attribute fsinfo_attributes[] = {
+	FSINFO_VSTRUCT	(FSINFO_ATTR_STATFS,		fsinfo_generic_statfs),
+	FSINFO_VSTRUCT	(FSINFO_ATTR_IDS,		fsinfo_generic_ids),
+	FSINFO_VSTRUCT	(FSINFO_ATTR_LIMITS,		fsinfo_generic_limits),
+	FSINFO_VSTRUCT	(FSINFO_ATTR_SUPPORTS,		fsinfo_generic_supports),
+	FSINFO_VSTRUCT	(FSINFO_ATTR_TIMESTAMP_INFO,	fsinfo_generic_timestamp_info),
+	FSINFO_STRING	(FSINFO_ATTR_VOLUME_ID,		string),
+	FSINFO_VSTRUCT	(FSINFO_ATTR_VOLUME_UUID,	fsinfo_generic_volume_uuid),
+	FSINFO_STRING	(FSINFO_ATTR_VOLUME_NAME,	string),
+	FSINFO_VSTRUCT_N(FSINFO_ATTR_FSINFO_ATTRIBUTE_INFO, fsinfo_meta_attribute_info),
+	FSINFO_LIST	(FSINFO_ATTR_FSINFO_ATTRIBUTES,	fsinfo_meta_attributes),
+	{}
+};
+
+static __attribute__((noreturn))
+void bad_value(const char *what,
+	       struct fsinfo_params *params,
+	       const struct fsinfo_attribute *attr,
+	       const struct fsinfo_attribute_info *attr_info,
+	       void *reply, unsigned int size)
+{
+	printf("\n");
+	fprintf(stderr, "%s %s{%u}{%u} t=%x f=%x s=%x\n",
+		what, attr->name, params->Nth, params->Mth,
+		attr_info->type, attr_info->flags, attr_info->size);
+	fprintf(stderr, "size=%u\n", size);
+	dump_hex(stderr, reply, 0, size);
+	exit(1);
+}
+
+static void dump_value(unsigned int attr_id,
+		       const struct fsinfo_attribute *attr,
+		       const struct fsinfo_attribute_info *attr_info,
+		       void *reply, unsigned int size)
+{
+	if (!attr || !attr->dump) {
+		printf("<no dumper>\n");
+		return;
+	}
+
+	if (attr->type == FSINFO_TYPE_VSTRUCT && size < attr->size) {
+		printf("<short data %u/%u>\n", size, attr->size);
+		return;
+	}
+
+	attr->dump(reply, size);
+}
+
+static void dump_list(unsigned int attr_id,
+		      const struct fsinfo_attribute *attr,
+		      const struct fsinfo_attribute_info *attr_info,
+		      void *reply, unsigned int size)
+{
+	size_t elem_size = attr_info->size;
+	unsigned int ix = 0;
+
+	printf("\n");
+	if (!attr || !attr->dump) {
+		printf("<no dumper>\n");
+		return;
+	}
+
+	if (attr->type == FSINFO_TYPE_VSTRUCT && size < attr->size) {
+		printf("<short data %u/%u>\n", size, attr->size);
+		return;
+	}
+
+	list_last = false;
+	while (size >= elem_size) {
+		printf("\t[%02x] ", ix);
+		if (size == elem_size)
+			list_last = true;
+		attr->dump(reply, size);
+		reply += elem_size;
+		size -= elem_size;
+		ix++;
+	}
+}
+
+/*
+ * Call fsinfo, expanding the buffer as necessary.
+ */
+static ssize_t get_fsinfo(const char *file, const char *name,
+			  struct fsinfo_params *params, void **_r)
+{
+	ssize_t ret;
+	size_t buf_size = 4096;
+	void *r;
+
+	for (;;) {
+		r = malloc(buf_size);
+		if (!r) {
+			perror("malloc");
+			exit(1);
+		}
+		memset(r, 0xbd, buf_size);
+
+		errno = 0;
+		ret = fsinfo(AT_FDCWD, file, params, sizeof(*params), r, buf_size - 1);
+		if (ret == -1)
+			goto error;
+
+		if (ret <= buf_size - 1)
+			break;
+		buf_size = (ret + 4096 - 1) & ~(4096 - 1);
+	}
+
+	if (debug)
+		printf("fsinfo(%s,%s,%u,%u) = %zd\n",
+		       file, name, params->Nth, params->Mth, ret);
+
+	((char *)r)[ret] = 0;
+	*_r = r;
+	return ret;
+
+error:
+	*_r = NULL;
+	free(r);
+	if (debug)
+		printf("fsinfo(%s,%s,%u,%u) = %m\n",
+		       file, name, params->Nth, params->Mth);
+	return ret;
+}
+
+/*
+ * Try one subinstance of an attribute.
+ */
+static int try_one(const char *file, struct fsinfo_params *params,
+		   const struct fsinfo_attribute_info *attr_info, bool raw)
+{
+	const struct fsinfo_attribute *attr;
+	const char *name;
+	size_t size = 4096;
+	char namebuf[32];
+	void *r;
+
+	for (attr = fsinfo_attributes; attr->name; attr++) {
+		if (attr->attr_id == params->request) {
+			name = attr->name;
+			if (strncmp(name, "fsinfo_generic_", 15) == 0)
+				name += 15;
+			goto found;
+		}
+	}
+
+	sprintf(namebuf, "<unknown-%x>", params->request);
+	name = namebuf;
+	attr = NULL;
+
+found:
+	size = get_fsinfo(file, name, params, &r);
+
+	if (size == -1) {
+		if (errno == ENODATA) {
+			if (!(attr_info->flags & (FSINFO_FLAGS_N | FSINFO_FLAGS_NM)) &&
+			    params->Nth == 0 && params->Mth == 0)
+				bad_value("Unexpected ENODATA",
+					  params, attr, attr_info, r, size);
+			free(r);
+			return (params->Mth == 0) ? 2 : 1;
+		}
+		if (errno == EOPNOTSUPP) {
+			if (params->Nth > 0 || params->Mth > 0)
+				bad_value("Should return ENODATA",
+					  params, attr, attr_info, r, size);
+			//printf("\e[33m%s\e[m: <not supported>\n",
+			//       fsinfo_attr_names[attr]);
+			free(r);
+			return 2;
+		}
+		perror(file);
+		exit(1);
+	}
+
+	if (raw) {
+		if (size > 4096)
+			size = 4096;
+		dump_hex(stdout, r, 0, size);
+		free(r);
+		return 0;
+	}
+
+	switch (attr_info->flags & (FSINFO_FLAGS_N | FSINFO_FLAGS_NM)) {
+	case 0:
+		printf("\e[33m%s\e[m: ", name);
+		break;
+	case FSINFO_FLAGS_N:
+		printf("\e[33m%s{%u}\e[m: ", name, params->Nth);
+		break;
+	case FSINFO_FLAGS_NM:
+		printf("\e[33m%s{%u,%u}\e[m: ", name, params->Nth, params->Mth);
+		break;
+	}
+
+	switch (attr_info->type) {
+	case FSINFO_TYPE_STRING:
+		if (size == 0 || ((char *)r)[size - 1] != 0)
+			bad_value("Unterminated string",
+				  params, attr, attr_info, r, size);
+	case FSINFO_TYPE_VSTRUCT:
+	case FSINFO_TYPE_OPAQUE:
+		dump_value(params->request, attr, attr_info, r, size);
+		free(r);
+		return 0;
+
+	case FSINFO_TYPE_LIST:
+		dump_list(params->request, attr, attr_info, r, size);
+		free(r);
+		return 0;
+
+	default:
+		bad_value("Fishy type", params, attr, attr_info, r, size);
+	}
+}
+
+static int cmp_u32(const void *a, const void *b)
+{
+	return *(const int *)a - *(const int *)b;
+}
+
+/*
+ *
+ */
+int main(int argc, char **argv)
+{
+	struct fsinfo_attribute_info attr_info;
+	struct fsinfo_params params = {
+		.at_flags	= AT_SYMLINK_NOFOLLOW,
+		.flags		= FSINFO_FLAGS_QUERY_PATH,
+	};
+	unsigned int *attrs, ret, nr, i;
+	bool meta = false;
+	int raw = 0, opt, Nth, Mth;
+
+	while ((opt = getopt(argc, argv, "Madlr"))) {
+		switch (opt) {
+		case 'M':
+			meta = true;
+			continue;
+		case 'a':
+			params.at_flags |= AT_NO_AUTOMOUNT;
+			params.flags = FSINFO_FLAGS_QUERY_PATH;
+			continue;
+		case 'd':
+			debug = true;
+			continue;
+		case 'l':
+			params.at_flags &= ~AT_SYMLINK_NOFOLLOW;
+			params.flags = FSINFO_FLAGS_QUERY_PATH;
+			continue;
+		case 'r':
+			raw = 1;
+			continue;
+		}
+		break;
+	}
+
+	argc -= optind;
+	argv += optind;
+
+	if (argc != 1) {
+		printf("Format: test-fsinfo [-Madlr] <path>\n");
+		exit(2);
+	}
+
+	/* Retrieve a list of supported attribute IDs */
+	params.request = FSINFO_ATTR_FSINFO_ATTRIBUTES;
+	params.Nth = 0;
+	params.Mth = 0;
+	ret = get_fsinfo(argv[0], "attributes", &params, (void **)&attrs);
+	if (ret == -1) {
+		fprintf(stderr, "Unable to get attribute list: %m\n");
+		exit(1);
+	}
+
+	if (ret % sizeof(attrs[0])) {
+		fprintf(stderr, "Bad length of attribute list (0x%x)\n", ret);
+		exit(2);
+	}
+
+	nr = ret / sizeof(attrs[0]);
+	qsort(attrs, nr, sizeof(attrs[0]), cmp_u32);
+
+	if (meta) {
+		printf("ATTR ID  TYPE         FLAGS    SIZE  NAME\n");
+		printf("======== ============ ======== ===== =========\n");
+		for (i = 0; i < nr; i++) {
+			params.request = FSINFO_ATTR_FSINFO_ATTRIBUTE_INFO;
+			params.Nth = attrs[i];
+			params.Mth = 0;
+			ret = fsinfo(AT_FDCWD, argv[0],
+				     &params, sizeof(params),
+				     &attr_info, sizeof(attr_info));
+			if (ret == -1) {
+				fprintf(stderr, "Can't get info for attribute %x: %m\n", attrs[i]);
+				exit(1);
+			}
+
+			dump_attribute_info(&attr_info, ret);
+		}
+		exit(0);
+	}
+
+	for (i = 0; i < nr; i++) {
+		params.request = FSINFO_ATTR_FSINFO_ATTRIBUTE_INFO;
+		params.Nth = attrs[i];
+		params.Mth = 0;
+		ret = fsinfo(AT_FDCWD, argv[0],
+			     &params, sizeof(params),
+			     &attr_info, sizeof(attr_info));
+		if (ret == -1) {
+			fprintf(stderr, "Can't get info for attribute %x: %m\n", attrs[i]);
+			exit(1);
+		}
+
+		if (attrs[i] == FSINFO_ATTR_FSINFO_ATTRIBUTE_INFO ||
+		    attrs[i] == FSINFO_ATTR_FSINFO_ATTRIBUTES)
+			continue;
+
+		if (attrs[i] != attr_info.attr_id) {
+			fprintf(stderr, "ID for %03x returned %03x\n",
+				attrs[i], attr_info.attr_id);
+			break;
+		}
+		Nth = 0;
+		do {
+			Mth = 0;
+			do {
+				params.request = attrs[i];
+				params.Nth = Nth;
+				params.Mth = Mth;
+
+				switch (try_one(argv[0], &params, &attr_info, raw)) {
+				case 0:
+					continue;
+				case 1:
+					goto done_M;
+				case 2:
+					goto done_N;
+				}
+			} while (++Mth < 100);
+
+		done_M:
+			if (Mth >= 100) {
+				fprintf(stderr, "Fishy: Mth %x[%u][%u]\n", attrs[i], Nth, Mth);
+				break;
+			}
+
+		} while (++Nth < 100);
+
+	done_N:
+		if (Nth >= 100) {
+			fprintf(stderr, "Fishy: Nth %x[%u]\n", attrs[i], Nth);
+			break;
+		}
+	}
+
+	return 0;
+}