diff mbox series

[RESEND,V12,3/8] fuse: Definitions and ioctl for passthrough

Message ID 20210125153057.3623715-4-balsini@android.com (mailing list archive)
State New
Headers show
Series fuse: Add support for passthrough read/write | expand

Commit Message

Alessio Balsini Jan. 25, 2021, 3:30 p.m. UTC
Expose the FUSE_PASSTHROUGH interface to user space and declare all the
basic data structures and functions as the skeleton on top of which the
FUSE passthrough functionality will be built.

As part of this, introduce the new FUSE passthrough ioctl, which allows
the FUSE daemon to specify a direct connection between a FUSE file and a
lower file system file. Such ioctl requires user space to pass the file
descriptor of one of its opened files through the fuse_passthrough_out
data structure introduced in this patch. This structure includes extra
fields for possible future extensions.
Also, add the passthrough functions for the set-up and tear-down of the
data structures and locks that will be used both when fuse_conns and
fuse_files are created/deleted.

Signed-off-by: Alessio Balsini <balsini@android.com>
---
 fs/fuse/Makefile          |  1 +
 fs/fuse/dev.c             | 12 ++++++++++++
 fs/fuse/dir.c             |  2 ++
 fs/fuse/file.c            |  4 +++-
 fs/fuse/fuse_i.h          | 27 +++++++++++++++++++++++++++
 fs/fuse/inode.c           | 17 ++++++++++++++++-
 fs/fuse/passthrough.c     | 21 +++++++++++++++++++++
 include/uapi/linux/fuse.h | 11 ++++++++++-
 8 files changed, 92 insertions(+), 3 deletions(-)
 create mode 100644 fs/fuse/passthrough.c

Comments

Miklos Szeredi Feb. 17, 2021, 1:41 p.m. UTC | #1
On Mon, Jan 25, 2021 at 4:31 PM Alessio Balsini <balsini@android.com> wrote:
>
> Expose the FUSE_PASSTHROUGH interface to user space and declare all the
> basic data structures and functions as the skeleton on top of which the
> FUSE passthrough functionality will be built.
>
> As part of this, introduce the new FUSE passthrough ioctl, which allows
> the FUSE daemon to specify a direct connection between a FUSE file and a
> lower file system file. Such ioctl requires user space to pass the file
> descriptor of one of its opened files through the fuse_passthrough_out
> data structure introduced in this patch. This structure includes extra
> fields for possible future extensions.
> Also, add the passthrough functions for the set-up and tear-down of the
> data structures and locks that will be used both when fuse_conns and
> fuse_files are created/deleted.
>
> Signed-off-by: Alessio Balsini <balsini@android.com>

[...]

> diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
> index 54442612c48b..9d7685ce0acd 100644
> --- a/include/uapi/linux/fuse.h
> +++ b/include/uapi/linux/fuse.h
> @@ -360,6 +360,7 @@ struct fuse_file_lock {
>  #define FUSE_MAP_ALIGNMENT     (1 << 26)
>  #define FUSE_SUBMOUNTS         (1 << 27)
>  #define FUSE_HANDLE_KILLPRIV_V2        (1 << 28)
> +#define FUSE_PASSTHROUGH       (1 << 29)

This header has a version and a changelog.  Please update those as well.

>
>  /**
>   * CUSE INIT request/reply flags
> @@ -625,7 +626,7 @@ struct fuse_create_in {
>  struct fuse_open_out {
>         uint64_t        fh;
>         uint32_t        open_flags;
> -       uint32_t        padding;
> +       uint32_t        passthrough_fh;

I think it would be cleaner to add a FOPEN_PASSTHROUGH flag to
explicitly request passthrough instead of just passing a non-null
value to passthrough_fh.

>  };
>
>  struct fuse_release_in {
> @@ -828,6 +829,13 @@ struct fuse_in_header {
>         uint32_t        padding;
>  };
>
> +struct fuse_passthrough_out {
> +       uint32_t        fd;
> +       /* For future implementation */
> +       uint32_t        len;
> +       void            *vec;
> +};

I don't see why we'd need these extensions.    The ioctl just needs to
establish an ID to open file mapping that can be referenced on the
regular protocol, i.e. it just needs to be passed an open file
descriptor and return an unique ID.

Mapping the fuse file's data to the underlying file's data is a
different matter.  That can be an identity mapping established at open
time (this is what this series does) or it can be an arbitrary extent
mapping to one or more underlying open files, established at open time
or on demand.  All of these can be done in band using the fuse
protocol, no need to involve the ioctl mechanism.

So I think we can just get rid of "struct fuse_passthrough_out"
completely and use "uint32_t *" as the ioctl argument.

What I think would be useful is to have an explicit
FUSE_DEV_IOC_PASSTHROUGH_CLOSE ioctl, that would need to be called
once the fuse server no longer needs this ID.   If this turns out to
be a performance problem, we could still add the auto-close behavior
with an explicit FOPEN_PASSTHROUGH_AUTOCLOSE flag later.

Thanks,
Miklos
Peng Tao Feb. 19, 2021, 7:05 a.m. UTC | #2
On Wed, Feb 17, 2021 at 9:41 PM Miklos Szeredi <miklos@szeredi.hu> wrote:
>
> On Mon, Jan 25, 2021 at 4:31 PM Alessio Balsini <balsini@android.com> wrote:
> >
> > Expose the FUSE_PASSTHROUGH interface to user space and declare all the
> > basic data structures and functions as the skeleton on top of which the
> > FUSE passthrough functionality will be built.
> >
> > As part of this, introduce the new FUSE passthrough ioctl, which allows
> > the FUSE daemon to specify a direct connection between a FUSE file and a
> > lower file system file. Such ioctl requires user space to pass the file
> > descriptor of one of its opened files through the fuse_passthrough_out
> > data structure introduced in this patch. This structure includes extra
> > fields for possible future extensions.
> > Also, add the passthrough functions for the set-up and tear-down of the
> > data structures and locks that will be used both when fuse_conns and
> > fuse_files are created/deleted.
> >
> > Signed-off-by: Alessio Balsini <balsini@android.com>
>
> [...]
>
> > diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
> > index 54442612c48b..9d7685ce0acd 100644
> > --- a/include/uapi/linux/fuse.h
> > +++ b/include/uapi/linux/fuse.h
> > @@ -360,6 +360,7 @@ struct fuse_file_lock {
> >  #define FUSE_MAP_ALIGNMENT     (1 << 26)
> >  #define FUSE_SUBMOUNTS         (1 << 27)
> >  #define FUSE_HANDLE_KILLPRIV_V2        (1 << 28)
> > +#define FUSE_PASSTHROUGH       (1 << 29)
>
> This header has a version and a changelog.  Please update those as well.
>
> >
> >  /**
> >   * CUSE INIT request/reply flags
> > @@ -625,7 +626,7 @@ struct fuse_create_in {
> >  struct fuse_open_out {
> >         uint64_t        fh;
> >         uint32_t        open_flags;
> > -       uint32_t        padding;
> > +       uint32_t        passthrough_fh;
>
> I think it would be cleaner to add a FOPEN_PASSTHROUGH flag to
> explicitly request passthrough instead of just passing a non-null
> value to passthrough_fh.
>
> >  };
> >
> >  struct fuse_release_in {
> > @@ -828,6 +829,13 @@ struct fuse_in_header {
> >         uint32_t        padding;
> >  };
> >
> > +struct fuse_passthrough_out {
> > +       uint32_t        fd;
> > +       /* For future implementation */
> > +       uint32_t        len;
> > +       void            *vec;
> > +};
>
> I don't see why we'd need these extensions.    The ioctl just needs to
> establish an ID to open file mapping that can be referenced on the
> regular protocol, i.e. it just needs to be passed an open file
> descriptor and return an unique ID.
>
> Mapping the fuse file's data to the underlying file's data is a
> different matter.  That can be an identity mapping established at open
> time (this is what this series does) or it can be an arbitrary extent
> mapping to one or more underlying open files, established at open time
> or on demand.  All of these can be done in band using the fuse
> protocol, no need to involve the ioctl mechanism.
>
> So I think we can just get rid of "struct fuse_passthrough_out"
> completely and use "uint32_t *" as the ioctl argument.
>
> What I think would be useful is to have an explicit
> FUSE_DEV_IOC_PASSTHROUGH_CLOSE ioctl, that would need to be called
> once the fuse server no longer needs this ID.   If this turns out to
> be a performance problem, we could still add the auto-close behavior
> with an explicit FOPEN_PASSTHROUGH_AUTOCLOSE flag later.
Hi Miklos,

W/o auto closing, what happens if user space daemon forgets to call
FUSE_DEV_IOC_PASSTHROUGH_CLOSE? Do we keep the ID alive somewhere?

Thanks,
Tao
Miklos Szeredi Feb. 19, 2021, 8:40 a.m. UTC | #3
On Fri, Feb 19, 2021 at 8:05 AM Peng Tao <bergwolf@gmail.com> wrote:
>
> On Wed, Feb 17, 2021 at 9:41 PM Miklos Szeredi <miklos@szeredi.hu> wrote:

> > What I think would be useful is to have an explicit
> > FUSE_DEV_IOC_PASSTHROUGH_CLOSE ioctl, that would need to be called
> > once the fuse server no longer needs this ID.   If this turns out to
> > be a performance problem, we could still add the auto-close behavior
> > with an explicit FOPEN_PASSTHROUGH_AUTOCLOSE flag later.
> Hi Miklos,
>
> W/o auto closing, what happens if user space daemon forgets to call
> FUSE_DEV_IOC_PASSTHROUGH_CLOSE? Do we keep the ID alive somewhere?

Kernel would keep the ID open until explicit close or fuse connection
is released.

There should be some limit on the max open files referenced through
ID's, though.   E.g. inherit RLIMIT_NOFILE from mounting task.

Thanks,
Miklos
diff mbox series

Patch

diff --git a/fs/fuse/Makefile b/fs/fuse/Makefile
index 8c7021fb2cd4..20ed23aa16fa 100644
--- a/fs/fuse/Makefile
+++ b/fs/fuse/Makefile
@@ -8,6 +8,7 @@  obj-$(CONFIG_CUSE) += cuse.o
 obj-$(CONFIG_VIRTIO_FS) += virtiofs.o
 
 fuse-y := dev.o dir.o file.o inode.o control.o xattr.o acl.o readdir.o
+fuse-y += passthrough.o
 fuse-$(CONFIG_FUSE_DAX) += dax.o
 
 virtiofs-y := virtio_fs.o
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index ff9f3b83f879..5446f13db5a0 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -2236,6 +2236,7 @@  static long fuse_dev_ioctl(struct file *file, unsigned int cmd,
 	int res;
 	int oldfd;
 	struct fuse_dev *fud = NULL;
+	struct fuse_passthrough_out pto;
 
 	if (_IOC_TYPE(cmd) != FUSE_DEV_IOC_MAGIC)
 		return -EINVAL;
@@ -2266,6 +2267,17 @@  static long fuse_dev_ioctl(struct file *file, unsigned int cmd,
 			}
 		}
 		break;
+	case _IOC_NR(FUSE_DEV_IOC_PASSTHROUGH_OPEN):
+		res = -EFAULT;
+		if (!copy_from_user(&pto,
+				    (struct fuse_passthrough_out __user *)arg,
+				    sizeof(pto))) {
+			res = -EINVAL;
+			fud = fuse_get_dev(file);
+			if (fud)
+				res = fuse_passthrough_open(fud, &pto);
+		}
+		break;
 	default:
 		res = -ENOTTY;
 		break;
diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 78f9f209078c..c9a1b33c5481 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -513,6 +513,7 @@  static int fuse_create_open(struct inode *dir, struct dentry *entry,
 {
 	int err;
 	struct inode *inode;
+	struct fuse_conn *fc = get_fuse_conn(dir);
 	struct fuse_mount *fm = get_fuse_mount(dir);
 	FUSE_ARGS(args);
 	struct fuse_forget_link *forget;
@@ -574,6 +575,7 @@  static int fuse_create_open(struct inode *dir, struct dentry *entry,
 	ff->fh = outopen.fh;
 	ff->nodeid = outentry.nodeid;
 	ff->open_flags = outopen.open_flags;
+	fuse_passthrough_setup(fc, ff, &outopen);
 	inode = fuse_iget(dir->i_sb, outentry.nodeid, outentry.generation,
 			  &outentry.attr, entry_attr_timeout(&outentry), 0);
 	if (!inode) {
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 8cccecb55fb8..953f3034c375 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -158,7 +158,7 @@  int fuse_do_open(struct fuse_mount *fm, u64 nodeid, struct file *file,
 		if (!err) {
 			ff->fh = outarg.fh;
 			ff->open_flags = outarg.open_flags;
-
+			fuse_passthrough_setup(fc, ff, &outarg);
 		} else if (err != -ENOSYS) {
 			fuse_file_free(ff);
 			return err;
@@ -304,6 +304,8 @@  void fuse_release_common(struct file *file, bool isdir)
 	struct fuse_release_args *ra = ff->release_args;
 	int opcode = isdir ? FUSE_RELEASEDIR : FUSE_RELEASE;
 
+	fuse_passthrough_release(&ff->passthrough);
+
 	fuse_prepare_release(fi, ff, file->f_flags, opcode);
 
 	if (ff->flock) {
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 7c4b8cb93f9f..8d39f5304a11 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -180,6 +180,14 @@  struct fuse_conn;
 struct fuse_mount;
 struct fuse_release_args;
 
+/**
+ * Reference to lower filesystem file for read/write operations handled in
+ * passthrough mode
+ */
+struct fuse_passthrough {
+	struct file *filp;
+};
+
 /** FUSE specific file data */
 struct fuse_file {
 	/** Fuse connection for this file */
@@ -225,6 +233,9 @@  struct fuse_file {
 
 	} readdir;
 
+	/** Container for data related to the passthrough functionality */
+	struct fuse_passthrough passthrough;
+
 	/** RB node to be linked on fuse_conn->polled_files */
 	struct rb_node polled_node;
 
@@ -755,6 +766,9 @@  struct fuse_conn {
 	/* Auto-mount submounts announced by the server */
 	unsigned int auto_submounts:1;
 
+	/** Passthrough mode for read/write IO */
+	unsigned int passthrough:1;
+
 	/** The number of requests waiting for completion */
 	atomic_t num_waiting;
 
@@ -798,6 +812,12 @@  struct fuse_conn {
 
 	/** List of filesystems using this connection */
 	struct list_head mounts;
+
+	/** IDR for passthrough requests */
+	struct idr passthrough_req;
+
+	/** Protects passthrough_req */
+	spinlock_t passthrough_req_lock;
 };
 
 /*
@@ -1213,4 +1233,11 @@  void fuse_dax_inode_cleanup(struct inode *inode);
 bool fuse_dax_check_alignment(struct fuse_conn *fc, unsigned int map_alignment);
 void fuse_dax_cancel_work(struct fuse_conn *fc);
 
+/* passthrough.c */
+int fuse_passthrough_open(struct fuse_dev *fud,
+			  struct fuse_passthrough_out *pto);
+int fuse_passthrough_setup(struct fuse_conn *fc, struct fuse_file *ff,
+			   struct fuse_open_out *openarg);
+void fuse_passthrough_release(struct fuse_passthrough *passthrough);
+
 #endif /* _FS_FUSE_I_H */
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index b0e18b470e91..a1104d5abb70 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -691,6 +691,7 @@  void fuse_conn_init(struct fuse_conn *fc, struct fuse_mount *fm,
 	memset(fc, 0, sizeof(*fc));
 	spin_lock_init(&fc->lock);
 	spin_lock_init(&fc->bg_lock);
+	spin_lock_init(&fc->passthrough_req_lock);
 	init_rwsem(&fc->killsb);
 	refcount_set(&fc->count, 1);
 	atomic_set(&fc->dev_count, 1);
@@ -699,6 +700,7 @@  void fuse_conn_init(struct fuse_conn *fc, struct fuse_mount *fm,
 	INIT_LIST_HEAD(&fc->bg_queue);
 	INIT_LIST_HEAD(&fc->entry);
 	INIT_LIST_HEAD(&fc->devices);
+	idr_init(&fc->passthrough_req);
 	atomic_set(&fc->num_waiting, 0);
 	fc->max_background = FUSE_DEFAULT_MAX_BACKGROUND;
 	fc->congestion_threshold = FUSE_DEFAULT_CONGESTION_THRESHOLD;
@@ -1052,6 +1054,12 @@  static void process_init_reply(struct fuse_mount *fm, struct fuse_args *args,
 				fc->handle_killpriv_v2 = 1;
 				fm->sb->s_flags |= SB_NOSEC;
 			}
+			if (arg->flags & FUSE_PASSTHROUGH) {
+				fc->passthrough = 1;
+				/* Prevent further stacking */
+				fm->sb->s_stack_depth =
+					FILESYSTEM_MAX_STACK_DEPTH;
+			}
 		} else {
 			ra_pages = fc->max_read / PAGE_SIZE;
 			fc->no_lock = 1;
@@ -1095,7 +1103,7 @@  void fuse_send_init(struct fuse_mount *fm)
 		FUSE_PARALLEL_DIROPS | FUSE_HANDLE_KILLPRIV | FUSE_POSIX_ACL |
 		FUSE_ABORT_ERROR | FUSE_MAX_PAGES | FUSE_CACHE_SYMLINKS |
 		FUSE_NO_OPENDIR_SUPPORT | FUSE_EXPLICIT_INVAL_DATA |
-		FUSE_HANDLE_KILLPRIV_V2;
+		FUSE_HANDLE_KILLPRIV_V2 | FUSE_PASSTHROUGH;
 #ifdef CONFIG_FUSE_DAX
 	if (fm->fc->dax)
 		ia->in.flags |= FUSE_MAP_ALIGNMENT;
@@ -1123,9 +1131,16 @@  void fuse_send_init(struct fuse_mount *fm)
 }
 EXPORT_SYMBOL_GPL(fuse_send_init);
 
+static int free_fuse_passthrough(int id, void *p, void *data)
+{
+	return 0;
+}
+
 void fuse_free_conn(struct fuse_conn *fc)
 {
 	WARN_ON(!list_empty(&fc->devices));
+	idr_for_each(&fc->passthrough_req, free_fuse_passthrough, NULL);
+	idr_destroy(&fc->passthrough_req);
 	kfree_rcu(fc, rcu);
 }
 EXPORT_SYMBOL_GPL(fuse_free_conn);
diff --git a/fs/fuse/passthrough.c b/fs/fuse/passthrough.c
new file mode 100644
index 000000000000..594060c654f8
--- /dev/null
+++ b/fs/fuse/passthrough.c
@@ -0,0 +1,21 @@ 
+// SPDX-License-Identifier: GPL-2.0
+
+#include "fuse_i.h"
+
+#include <linux/fuse.h>
+
+int fuse_passthrough_open(struct fuse_dev *fud,
+			  struct fuse_passthrough_out *pto)
+{
+	return -EINVAL;
+}
+
+int fuse_passthrough_setup(struct fuse_conn *fc, struct fuse_file *ff,
+			   struct fuse_open_out *openarg)
+{
+	return -EINVAL;
+}
+
+void fuse_passthrough_release(struct fuse_passthrough *passthrough)
+{
+}
diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index 54442612c48b..9d7685ce0acd 100644
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -360,6 +360,7 @@  struct fuse_file_lock {
 #define FUSE_MAP_ALIGNMENT	(1 << 26)
 #define FUSE_SUBMOUNTS		(1 << 27)
 #define FUSE_HANDLE_KILLPRIV_V2	(1 << 28)
+#define FUSE_PASSTHROUGH	(1 << 29)
 
 /**
  * CUSE INIT request/reply flags
@@ -625,7 +626,7 @@  struct fuse_create_in {
 struct fuse_open_out {
 	uint64_t	fh;
 	uint32_t	open_flags;
-	uint32_t	padding;
+	uint32_t	passthrough_fh;
 };
 
 struct fuse_release_in {
@@ -828,6 +829,13 @@  struct fuse_in_header {
 	uint32_t	padding;
 };
 
+struct fuse_passthrough_out {
+	uint32_t	fd;
+	/* For future implementation */
+	uint32_t	len;
+	void		*vec;
+};
+
 struct fuse_out_header {
 	uint32_t	len;
 	int32_t		error;
@@ -905,6 +913,7 @@  struct fuse_notify_retrieve_in {
 /* Device ioctls: */
 #define FUSE_DEV_IOC_MAGIC		229
 #define FUSE_DEV_IOC_CLONE		_IOR(FUSE_DEV_IOC_MAGIC, 0, uint32_t)
+#define FUSE_DEV_IOC_PASSTHROUGH_OPEN	_IOW(FUSE_DEV_IOC_MAGIC, 1, struct fuse_passthrough_out)
 
 struct fuse_lseek_in {
 	uint64_t	fh;