diff mbox

[RFC,1/3] vfs: add copy_file_range syscall and vfs helper

Message ID 1428703236-24735-2-git-send-email-zab@redhat.com (mailing list archive)
State New, archived
Headers show

Commit Message

Zach Brown April 10, 2015, 10 p.m. UTC
Add a copy_file_range() system call for offloading copies between
regular files.

This gives an interface to underlying layers of the storage stack which
can copy without reading and writing all the data.  There are a few
candidates that should support copy offloading in the nearer term:

- btrfs shares extent references with its clone ioctl
- NFS has patches to add a COPY command which copies on the server
- SCSI has a family of XCOPY commands which copy in the device

This system call avoids the complexity of also accelerating the creation
of the destination file by operating on an existing destination file
descriptor, not a path.

Currently the high level vfs entry point limits copy offloading to files
on the same mount and super (and not in the same file).  This can be
relaxed if we get implementations which can copy between file systems
safely.

Signed-off-by: Zach Brown <zab@redhat.com>
---
 fs/read_write.c                   | 129 ++++++++++++++++++++++++++++++++++++++
 include/linux/fs.h                |   3 +
 include/uapi/asm-generic/unistd.h |   4 +-
 kernel/sys_ni.c                   |   1 +
 4 files changed, 136 insertions(+), 1 deletion(-)

Comments

Trond Myklebust April 10, 2015, 10:36 p.m. UTC | #1
Hi Zach,

On Fri, Apr 10, 2015 at 6:00 PM, Zach Brown <zab@redhat.com> wrote:
> Add a copy_file_range() system call for offloading copies between
> regular files.
>
> This gives an interface to underlying layers of the storage stack which
> can copy without reading and writing all the data.  There are a few
> candidates that should support copy offloading in the nearer term:
>
> - btrfs shares extent references with its clone ioctl
> - NFS has patches to add a COPY command which copies on the server
> - SCSI has a family of XCOPY commands which copy in the device
>
> This system call avoids the complexity of also accelerating the creation
> of the destination file by operating on an existing destination file
> descriptor, not a path.
>
> Currently the high level vfs entry point limits copy offloading to files
> on the same mount and super (and not in the same file).  This can be
> relaxed if we get implementations which can copy between file systems
> safely.
>
> Signed-off-by: Zach Brown <zab@redhat.com>
> ---
>  fs/read_write.c                   | 129 ++++++++++++++++++++++++++++++++++++++
>  include/linux/fs.h                |   3 +
>  include/uapi/asm-generic/unistd.h |   4 +-
>  kernel/sys_ni.c                   |   1 +
>  4 files changed, 136 insertions(+), 1 deletion(-)
>
> diff --git a/fs/read_write.c b/fs/read_write.c
> index 8e1b687..c65ce1d 100644
> --- a/fs/read_write.c
> +++ b/fs/read_write.c
> @@ -17,6 +17,7 @@
>  #include <linux/pagemap.h>
>  #include <linux/splice.h>
>  #include <linux/compat.h>
> +#include <linux/mount.h>
>  #include "internal.h"
>
>  #include <asm/uaccess.h>
> @@ -1424,3 +1425,131 @@ COMPAT_SYSCALL_DEFINE4(sendfile64, int, out_fd, int, in_fd,
>         return do_sendfile(out_fd, in_fd, NULL, count, 0);
>  }
>  #endif
> +
> +/*
> + * copy_file_range() differs from regular file read and write in that it
> + * specifically allows return partial success.  When it does so is up to
> + * the copy_file_range method.
> + */
> +ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
> +                           struct file *file_out, loff_t pos_out,
> +                           size_t len, int flags)

I'm going to repeat a gripe with this interface. I really don't think
we should treat copy_file_range() as taking a size_t length, since
that is not sufficient to do a full file copy on 32-bit systems w/ LFS
support.

Could we perhaps instead of a length, define a 'pos_in_start' and a
'pos_in_end' offset (with the latter being -1 for a full-file copy)
and then return an 'loff_t' value stating where the copy ended?

Note that both btrfs and NFSv4.2 allow for 64-bit lengths, so this
interface would be closer to what is already in use anyway.

Cheers
  Trond
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Andreas Dilger April 10, 2015, 11:01 p.m. UTC | #2
On Apr 10, 2015, at 4:00 PM, Zach Brown <zab@redhat.com> wrote:
> 
> Add a copy_file_range() system call for offloading copies between
> regular files.
> 
> This gives an interface to underlying layers of the storage stack which
> can copy without reading and writing all the data.  There are a few
> candidates that should support copy offloading in the nearer term:
> 
> - btrfs shares extent references with its clone ioctl
> - NFS has patches to add a COPY command which copies on the server
> - SCSI has a family of XCOPY commands which copy in the device
> 
> This system call avoids the complexity of also accelerating the creation
> of the destination file by operating on an existing destination file
> descriptor, not a path.
> 
> Currently the high level vfs entry point limits copy offloading to files
> on the same mount and super (and not in the same file).  This can be
> relaxed if we get implementations which can copy between file systems
> safely.
> 
> Signed-off-by: Zach Brown <zab@redhat.com>
> ---
> fs/read_write.c                   | 129 ++++++++++++++++++++++++++++++++++++++
> include/linux/fs.h                |   3 +
> include/uapi/asm-generic/unistd.h |   4 +-
> kernel/sys_ni.c                   |   1 +
> 4 files changed, 136 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/read_write.c b/fs/read_write.c
> index 8e1b687..c65ce1d 100644
> --- a/fs/read_write.c
> +++ b/fs/read_write.c
> @@ -17,6 +17,7 @@
> #include <linux/pagemap.h>
> #include <linux/splice.h>
> #include <linux/compat.h>
> +#include <linux/mount.h>
> #include "internal.h"
> 
> #include <asm/uaccess.h>
> @@ -1424,3 +1425,131 @@ COMPAT_SYSCALL_DEFINE4(sendfile64, int, out_fd, int, in_fd,
> 	return do_sendfile(out_fd, in_fd, NULL, count, 0);
> }
> #endif
> +
> +/*
> + * copy_file_range() differs from regular file read and write in that it
> + * specifically allows return partial success.  When it does so is up to
> + * the copy_file_range method.
> + */
> +ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
> +			    struct file *file_out, loff_t pos_out,
> +			    size_t len, int flags)

Minor nit - flags should be unsigned int to match the syscall.

> +{
> +	struct inode *inode_in;
> +	struct inode *inode_out;
> +	ssize_t ret;
> +
> +	if (flags)
> +		return -EINVAL;
> +
> +	if (len == 0)
> +		return 0;
> +
> +	/* copy_file_range allows full ssize_t len, ignoring MAX_RW_COUNT  */

This says "ssize_t", but the len parameter is "size_t"...

> +	ret = rw_verify_area(READ, file_in, &pos_in, len);
> +	if (ret >= 0)
> +		ret = rw_verify_area(WRITE, file_out, &pos_out, len);
> +	if (ret < 0)
> +		return ret;
> +
> +	if (!(file_in->f_mode & FMODE_READ) ||
> +	    !(file_out->f_mode & FMODE_WRITE) ||
> +	    (file_out->f_flags & O_APPEND) ||
> +	    !file_in->f_op || !file_in->f_op->copy_file_range)
> +		return -EINVAL;
> +
> +	inode_in = file_inode(file_in);
> +	inode_out = file_inode(file_out);
> +
> +	/* make sure offsets don't wrap and the input is inside i_size */
> +	if (pos_in + len < pos_in || pos_out + len < pos_out ||
> +	    pos_in + len > i_size_read(inode_in))
> +		return -EINVAL;
> +
> +	/* this could be relaxed once a method supports cross-fs copies */
> +	if (inode_in->i_sb != inode_out->i_sb ||
> +	    file_in->f_path.mnt != file_out->f_path.mnt)
> +		return -EXDEV;
> +
> +	/* forbid ranges in the same file */
> +	if (inode_in == inode_out)
> +		return -EINVAL;
> +
> +	ret = mnt_want_write_file(file_out);
> +	if (ret)
> +		return ret;
> +
> +	ret = file_in->f_op->copy_file_range(file_in, pos_in, file_out, pos_out,
> +					     len, flags);
> +	if (ret > 0) {
> +		fsnotify_access(file_in);
> +		add_rchar(current, ret);
> +		fsnotify_modify(file_out);
> +		add_wchar(current, ret);
> +	}
> +	inc_syscr(current);
> +	inc_syscw(current);
> +
> +	mnt_drop_write_file(file_out);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL(vfs_copy_file_range);
> +
> +SYSCALL_DEFINE6(copy_file_range, int, fd_in, loff_t __user *, off_in,
> +		int, fd_out, loff_t __user *, off_out,
> +		size_t, len, unsigned int, flags)
> +{
> +	loff_t pos_in;
> +	loff_t pos_out;
> +	struct fd f_in;
> +	struct fd f_out;
> +	ssize_t ret;
> +
> +	f_in = fdget(fd_in);
> +	f_out = fdget(fd_out);
> +	if (!f_in.file || !f_out.file) {
> +		ret = -EBADF;
> +		goto out;
> +	}
> +
> +	ret = -EFAULT;
> +	if (off_in) {
> +		if (copy_from_user(&pos_in, off_in, sizeof(loff_t)))
> +			goto out;
> +	} else {
> +		pos_in = f_in.file->f_pos;
> +	}
> +
> +	if (off_out) {
> +		if (copy_from_user(&pos_out, off_out, sizeof(loff_t)))
> +			goto out;
> +	} else {
> +		pos_out = f_out.file->f_pos;
> +	}
> +
> +	ret = vfs_copy_file_range(f_in.file, pos_in, f_out.file, pos_out, len,
> +				  flags);
> +	if (ret > 0) {
> +		pos_in += ret;
> +		pos_out += ret;
> +
> +		if (off_in) {
> +			if (copy_to_user(off_in, &pos_in, sizeof(loff_t)))
> +				ret = -EFAULT;
> +		} else {
> +			f_in.file->f_pos = pos_in;
> +		}
> +
> +		if (off_out) {
> +			if (copy_to_user(off_out, &pos_out, sizeof(loff_t)))
> +				ret = -EFAULT;
> +		} else {
> +			f_out.file->f_pos = pos_out;
> +		}
> +	}
> +out:
> +	fdput(f_in);
> +	fdput(f_out);
> +	return ret;
> +}
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index f4131e8..43a66d45 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1570,6 +1570,7 @@ struct file_operations {
> #ifndef CONFIG_MMU
> 	unsigned (*mmap_capabilities)(struct file *);
> #endif
> +	ssize_t (*copy_file_range)(struct file *, loff_t, struct file *, loff_t, size_t, int);

This should also be unsigned int for the flags parameter.

> };
> 
> struct inode_operations {
> @@ -1623,6 +1624,8 @@ extern ssize_t vfs_readv(struct file *, const struct iovec __user *,
> 		unsigned long, loff_t *);
> extern ssize_t vfs_writev(struct file *, const struct iovec __user *,
> 		unsigned long, loff_t *);
> +extern ssize_t vfs_copy_file_range(struct file *, loff_t , struct file *,
> +				   loff_t, size_t, int);
> 
> struct super_operations {
>    	struct inode *(*alloc_inode)(struct super_block *sb);
> diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
> index e016bd9..2b60f0c 100644
> --- a/include/uapi/asm-generic/unistd.h
> +++ b/include/uapi/asm-generic/unistd.h
> @@ -709,9 +709,11 @@ __SYSCALL(__NR_memfd_create, sys_memfd_create)
> __SYSCALL(__NR_bpf, sys_bpf)
> #define __NR_execveat 281
> __SC_COMP(__NR_execveat, sys_execveat, compat_sys_execveat)
> +#define __NR_copy_file_range 282
> +__SYSCALL(__NR_copy_file_range, sys_copy_file_range)
> 
> #undef __NR_syscalls
> -#define __NR_syscalls 282
> +#define __NR_syscalls 283
> 
> /*
>  * All syscalls below here should go away really,
> diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
> index 5adcb0a..07f4585 100644
> --- a/kernel/sys_ni.c
> +++ b/kernel/sys_ni.c
> @@ -159,6 +159,7 @@ cond_syscall(sys_uselib);
> cond_syscall(sys_fadvise64);
> cond_syscall(sys_fadvise64_64);
> cond_syscall(sys_madvise);
> +cond_syscall(sys_copy_file_range);
> 
> /* arch-specific weak syscall entries */
> cond_syscall(sys_pciconfig_read);
> -- 
> 2.1.0
> 
> --
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Cheers, Andreas





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Zach Brown April 11, 2015, 12:02 a.m. UTC | #3
On Fri, Apr 10, 2015 at 06:36:41PM -0400, Trond Myklebust wrote:
> On Fri, Apr 10, 2015 at 6:00 PM, Zach Brown <zab@redhat.com> wrote:

> > +
> > +/*
> > + * copy_file_range() differs from regular file read and write in that it
> > + * specifically allows return partial success.  When it does so is up to
> > + * the copy_file_range method.
> > + */
> > +ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
> > +                           struct file *file_out, loff_t pos_out,
> > +                           size_t len, int flags)
> 
> I'm going to repeat a gripe with this interface. I really don't think
> we should treat copy_file_range() as taking a size_t length, since
> that is not sufficient to do a full file copy on 32-bit systems w/ LFS
> support.

*nod*.  The length type is limited by the syscall return type and the
arbitrary desire to mimic read/write.

I sympathize with wanting to copy giant files with operations that don't
scale with file size because files can be enormous but sparse.

> Could we perhaps instead of a length, define a 'pos_in_start' and a
> 'pos_in_end' offset (with the latter being -1 for a full-file copy)
> and then return an 'loff_t' value stating where the copy ended?

Well, the resulting offset will be set if the caller provided it.  So
they could already be getting the copied length from that.  But they
might not specify the offsets.  Maybe they're just using the results to
total up a completion indicator.

Maybe we could make the length a pointer like the offsets that's set to
the copied length on return.

This all seems pretty gross.  Does anyone else have a vote?

(And I'll argue strongly against creating magical offset values that
change behaviour.  If we want to ignore arguments and get the length
from the source file we'd add a flag to do so.)

> Note that both btrfs and NFSv4.2 allow for 64-bit lengths, so this
> interface would be closer to what is already in use anyway.

Yeah, btrfs doesn't allow partial progress.  It returns 0 on success.
We could also do that but people have expressed an interest in returning
partial progress.

- z
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Trond Myklebust April 11, 2015, 12:24 a.m. UTC | #4
On Fri, Apr 10, 2015 at 8:02 PM, Zach Brown <zab@redhat.com> wrote:
> On Fri, Apr 10, 2015 at 06:36:41PM -0400, Trond Myklebust wrote:
>> On Fri, Apr 10, 2015 at 6:00 PM, Zach Brown <zab@redhat.com> wrote:
>
>> > +
>> > +/*
>> > + * copy_file_range() differs from regular file read and write in that it
>> > + * specifically allows return partial success.  When it does so is up to
>> > + * the copy_file_range method.
>> > + */
>> > +ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
>> > +                           struct file *file_out, loff_t pos_out,
>> > +                           size_t len, int flags)
>>
>> I'm going to repeat a gripe with this interface. I really don't think
>> we should treat copy_file_range() as taking a size_t length, since
>> that is not sufficient to do a full file copy on 32-bit systems w/ LFS
>> support.
>
> *nod*.  The length type is limited by the syscall return type and the
> arbitrary desire to mimic read/write.
>
> I sympathize with wanting to copy giant files with operations that don't
> scale with file size because files can be enormous but sparse.

The other argument against using a size_t is that there is no memory
buffer involved here. size_t is, after all, a type describing
in-memory objects, not files.

>> Could we perhaps instead of a length, define a 'pos_in_start' and a
>> 'pos_in_end' offset (with the latter being -1 for a full-file copy)
>> and then return an 'loff_t' value stating where the copy ended?
>
> Well, the resulting offset will be set if the caller provided it.  So
> they could already be getting the copied length from that.  But they
> might not specify the offsets.  Maybe they're just using the results to
> total up a completion indicator.
>
> Maybe we could make the length a pointer like the offsets that's set to
> the copied length on return.

That works, but why do we care so much about the difference between a
length and an offset as a return value?

To be fair, the NFS copy offload also allows the copy to proceed out
of order, in which case the range of copied data could be
non-contiguous in the case of a failure. However neither the length
nor the offset case will give you the full story in that case. Any
return value can at best be considered to define an offset range whose
contents need to be checked for success/failure.

> This all seems pretty gross.  Does anyone else have a vote?
>
> (And I'll argue strongly against creating magical offset values that
> change behaviour.  If we want to ignore arguments and get the length
> from the source file we'd add a flag to do so.)

The '-1' was not intended to be a special/magical value: as far as I'm
concerned any end offset that covers the full range of supported file
lengths would be OK.

>> Note that both btrfs and NFSv4.2 allow for 64-bit lengths, so this
>> interface would be closer to what is already in use anyway.
>
> Yeah, btrfs doesn't allow partial progress.  It returns 0 on success.
> We could also do that but people have expressed an interest in returning
> partial progress.

Returning an end offset would satisfy the partial progress requirement
(with the caveat mentioned above).

Cheers
  Trond
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Jeffrey Layton April 11, 2015, 1:04 p.m. UTC | #5
On Fri, 10 Apr 2015 20:24:06 -0400
Trond Myklebust <trond.myklebust@primarydata.com> wrote:

> On Fri, Apr 10, 2015 at 8:02 PM, Zach Brown <zab@redhat.com> wrote:
> > On Fri, Apr 10, 2015 at 06:36:41PM -0400, Trond Myklebust wrote:
> >> On Fri, Apr 10, 2015 at 6:00 PM, Zach Brown <zab@redhat.com> wrote:
> >
> >> > +
> >> > +/*
> >> > + * copy_file_range() differs from regular file read and write in that it
> >> > + * specifically allows return partial success.  When it does so is up to
> >> > + * the copy_file_range method.
> >> > + */
> >> > +ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
> >> > +                           struct file *file_out, loff_t pos_out,
> >> > +                           size_t len, int flags)
> >>
> >> I'm going to repeat a gripe with this interface. I really don't think
> >> we should treat copy_file_range() as taking a size_t length, since
> >> that is not sufficient to do a full file copy on 32-bit systems w/ LFS
> >> support.
> >
> > *nod*.  The length type is limited by the syscall return type and the
> > arbitrary desire to mimic read/write.
> >
> > I sympathize with wanting to copy giant files with operations that don't
> > scale with file size because files can be enormous but sparse.
> 
> The other argument against using a size_t is that there is no memory
> buffer involved here. size_t is, after all, a type describing
> in-memory objects, not files.
> 
> >> Could we perhaps instead of a length, define a 'pos_in_start' and a
> >> 'pos_in_end' offset (with the latter being -1 for a full-file copy)
> >> and then return an 'loff_t' value stating where the copy ended?
> >
> > Well, the resulting offset will be set if the caller provided it.  So
> > they could already be getting the copied length from that.  But they
> > might not specify the offsets.  Maybe they're just using the results to
> > total up a completion indicator.
> >
> > Maybe we could make the length a pointer like the offsets that's set to
> > the copied length on return.
> 
> That works, but why do we care so much about the difference between a
> length and an offset as a return value?
> 

I think it just comes down to potential confusion for users. What's
more useful, the number of bytes actually copied, or the offset into the
file where the copy ended?

I tend to the think an offset is more useful for someone trying to
copy a file in chunks, particularly if the file is sparse. That gives
them a clear place to continue the copy.

So, I think I agree with Trond that phrasing this interface in terms of
file offsets seems like it might be more useful. That also neatly
sidesteps the size_t limitations on 32-bit platforms.

> To be fair, the NFS copy offload also allows the copy to proceed out
> of order, in which case the range of copied data could be
> non-contiguous in the case of a failure. However neither the length
> nor the offset case will give you the full story in that case. Any
> return value can at best be considered to define an offset range whose
> contents need to be checked for success/failure.
> 

Yuck! How the heck do you clean up the mess if that happens? I guess
you're just stuck redoing the copy with normal READ/WRITE?

Maybe we need to have the interface return a hard error in that
case and not try to give back any sort of offset?

> > This all seems pretty gross.  Does anyone else have a vote?
> >
> > (And I'll argue strongly against creating magical offset values that
> > change behaviour.  If we want to ignore arguments and get the length
> > from the source file we'd add a flag to do so.)
> 
> The '-1' was not intended to be a special/magical value: as far as I'm
> concerned any end offset that covers the full range of supported file
> lengths would be OK.
> 

Agreed. A "whole file" flag might also be useful too, but I'd leave
that for after the initial implementation is merged, just in the
interest of having _something_ that works in the near term.

> >> Note that both btrfs and NFSv4.2 allow for 64-bit lengths, so this
> >> interface would be closer to what is already in use anyway.
> >
> > Yeah, btrfs doesn't allow partial progress.  It returns 0 on success.
> > We could also do that but people have expressed an interest in returning
> > partial progress.
> 
> Returning an end offset would satisfy the partial progress requirement
> (with the caveat mentioned above).
>
Zach Brown April 13, 2015, 4:32 p.m. UTC | #6
> > >> Could we perhaps instead of a length, define a 'pos_in_start' and a
> > >> 'pos_in_end' offset (with the latter being -1 for a full-file copy)
> > >> and then return an 'loff_t' value stating where the copy ended?
> > >
> > > Well, the resulting offset will be set if the caller provided it.  So
> > > they could already be getting the copied length from that.  But they
> > > might not specify the offsets.  Maybe they're just using the results to
> > > total up a completion indicator.
> > >
> > > Maybe we could make the length a pointer like the offsets that's set to
> > > the copied length on return.
> > 
> > That works, but why do we care so much about the difference between a
> > length and an offset as a return value?
> > 
> 
> I think it just comes down to potential confusion for users. What's
> more useful, the number of bytes actually copied, or the offset into the
> file where the copy ended?
> 
> I tend to the think an offset is more useful for someone trying to
> copy a file in chunks, particularly if the file is sparse. That gives
> them a clear place to continue the copy.
> 
> So, I think I agree with Trond that phrasing this interface in terms of
> file offsets seems like it might be more useful. That also neatly
> sidesteps the size_t limitations on 32-bit platforms.

Yeah, fair enough.  I'll rework it.

> > To be fair, the NFS copy offload also allows the copy to proceed out
> > of order, in which case the range of copied data could be
> > non-contiguous in the case of a failure. However neither the length
> > nor the offset case will give you the full story in that case. Any
> > return value can at best be considered to define an offset range whose
> > contents need to be checked for success/failure.
> > 
> 
> Yuck! How the heck do you clean up the mess if that happens? I guess
> you're just stuck redoing the copy with normal READ/WRITE?

I don't think anyone will worry about checking file contents.

Yes, technically you can get fragmented completion past the initial
contiguous region that the interface told you is done.   You can get
that with O_DIRECT today.

But it's a rare case that is not worth worrying about.  You'll retry at
the contiguous offset until it doesn't make progress and then fall back
to read/write.

- z
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Christoph Hellwig April 14, 2015, 4:53 p.m. UTC | #7
On Sat, Apr 11, 2015 at 09:04:02AM -0400, Jeff Layton wrote:
> Yuck! How the heck do you clean up the mess if that happens? I guess
> you're just stuck redoing the copy with normal READ/WRITE?
> 
> Maybe we need to have the interface return a hard error in that
> case and not try to give back any sort of offset?

The NFSv4.2 COPY interface is a train wreck.  At least for Linux I'd
expect us to simply ignore it and only implement my new CLONE operation
with sane semantics.  That is unless someone can show some real life
use case for the inter server copy, in which case we'll have to deal
with that mess.  But getting that one right at the VFS level will
be a nightmare anyway.

Make this a vote from me to not support partial copies and just return
and error in that case.
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Christoph Hellwig April 14, 2015, 4:58 p.m. UTC | #8
On Tue, Apr 14, 2015 at 09:53:44AM -0700, Christoph Hellwig wrote:
> On Sat, Apr 11, 2015 at 09:04:02AM -0400, Jeff Layton wrote:
> > Yuck! How the heck do you clean up the mess if that happens? I guess
> > you're just stuck redoing the copy with normal READ/WRITE?
> > 
> > Maybe we need to have the interface return a hard error in that
> > case and not try to give back any sort of offset?
> 
> The NFSv4.2 COPY interface is a train wreck.  At least for Linux I'd
> expect us to simply ignore it and only implement my new CLONE operation
> with sane semantics.  That is unless someone can show some real life
> use case for the inter server copy, in which case we'll have to deal
> with that mess.  But getting that one right at the VFS level will
> be a nightmare anyway.

Btw, in case someone cares about the NFS CLONE implementation here is
my prototype based on Anna's older COPY prototype.  It's simple enough that
it might be worth adding to the copy_file_range patch set.

http://git.infradead.org/users/hch/pnfs.git/shortlog/refs/heads/clone
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Anna Schumaker April 14, 2015, 5:16 p.m. UTC | #9
On 04/14/2015 12:53 PM, Christoph Hellwig wrote:
> On Sat, Apr 11, 2015 at 09:04:02AM -0400, Jeff Layton wrote:
>> Yuck! How the heck do you clean up the mess if that happens? I guess
>> you're just stuck redoing the copy with normal READ/WRITE?
>>
>> Maybe we need to have the interface return a hard error in that
>> case and not try to give back any sort of offset?
> 
> The NFSv4.2 COPY interface is a train wreck.  At least for Linux I'd
> expect us to simply ignore it and only implement my new CLONE operation
> with sane semantics.  That is unless someone can show some real life
> use case for the inter server copy, in which case we'll have to deal
> with that mess.  But getting that one right at the VFS level will
> be a nightmare anyway.
> 
> Make this a vote from me to not support partial copies and just return
> and error in that case.

Agreed.  Looking at the v4.2 spec, COPY does take ca_consecutive and a ca_synchronous flags that let the client state if the copy should be done consecutively or synchronously.  I expected to always set consecutive to "true" for the Linux client.

Anna

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J. Bruce Fields April 14, 2015, 6:19 p.m. UTC | #10
On Tue, Apr 14, 2015 at 01:16:13PM -0400, Anna Schumaker wrote:
> On 04/14/2015 12:53 PM, Christoph Hellwig wrote:
> > On Sat, Apr 11, 2015 at 09:04:02AM -0400, Jeff Layton wrote:
> >> Yuck! How the heck do you clean up the mess if that happens? I
> >> guess you're just stuck redoing the copy with normal READ/WRITE?
> >>
> >> Maybe we need to have the interface return a hard error in that
> >> case and not try to give back any sort of offset?
> > 
> > The NFSv4.2 COPY interface is a train wreck.  At least for Linux I'd
> > expect us to simply ignore it and only implement my new CLONE
> > operation with sane semantics.  That is unless someone can show some
> > real life use case for the inter server copy, in which case we'll
> > have to deal with that mess.  But getting that one right at the VFS
> > level will be a nightmare anyway.
> > 
> > Make this a vote from me to not support partial copies and just
> > return and error in that case.
> 
> Agreed.  Looking at the v4.2 spec, COPY does take ca_consecutive and a
> ca_synchronous flags that let the client state if the copy should be
> done consecutively or synchronously.  I expected to always set
> consecutive to "true" for the Linux client.

That's supposed to mean results are well-defined in the partial-copy
case, but I think Christoph's suggesting eliminating the partial-copy
case entirely?

Which would be fine with me.

It might actually have been me advocating for partial copies.  But that
was only because a partial-copy-handling-loop seemed simpler to me than
progress callbacks if we were going to support long-running copies.

I'm happy enough not to have it at all.

--b.
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Zach Brown April 14, 2015, 6:22 p.m. UTC | #11
On Tue, Apr 14, 2015 at 02:19:11PM -0400, J. Bruce Fields wrote:
> On Tue, Apr 14, 2015 at 01:16:13PM -0400, Anna Schumaker wrote:
> > On 04/14/2015 12:53 PM, Christoph Hellwig wrote:
> > > On Sat, Apr 11, 2015 at 09:04:02AM -0400, Jeff Layton wrote:
> > >> Yuck! How the heck do you clean up the mess if that happens? I
> > >> guess you're just stuck redoing the copy with normal READ/WRITE?
> > >>
> > >> Maybe we need to have the interface return a hard error in that
> > >> case and not try to give back any sort of offset?
> > > 
> > > The NFSv4.2 COPY interface is a train wreck.  At least for Linux I'd
> > > expect us to simply ignore it and only implement my new CLONE
> > > operation with sane semantics.  That is unless someone can show some
> > > real life use case for the inter server copy, in which case we'll
> > > have to deal with that mess.  But getting that one right at the VFS
> > > level will be a nightmare anyway.
> > > 
> > > Make this a vote from me to not support partial copies and just
> > > return and error in that case.
> > 
> > Agreed.  Looking at the v4.2 spec, COPY does take ca_consecutive and a
> > ca_synchronous flags that let the client state if the copy should be
> > done consecutively or synchronously.  I expected to always set
> > consecutive to "true" for the Linux client.
> 
> That's supposed to mean results are well-defined in the partial-copy
> case, but I think Christoph's suggesting eliminating the partial-copy
> case entirely?
> 
> Which would be fine with me.
> 
> It might actually have been me advocating for partial copies.  But that
> was only because a partial-copy-handling-loop seemed simpler to me than
> progress callbacks if we were going to support long-running copies.
> 
> I'm happy enough not to have it at all.

Ah, OK, that's great news.

I thought at one point we were worried about very long running RPCs on
the server.  Are we not worried about that now?

Is the client expected to cut the work up into arbitrarily managable
chunks?  Is the server expected to fail COPY/CLONE requests that it
thinks would take way too long?  Something else?

- z
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J. Bruce Fields April 14, 2015, 6:29 p.m. UTC | #12
On Tue, Apr 14, 2015 at 11:22:41AM -0700, Zach Brown wrote:
> On Tue, Apr 14, 2015 at 02:19:11PM -0400, J. Bruce Fields wrote:
> > On Tue, Apr 14, 2015 at 01:16:13PM -0400, Anna Schumaker wrote:
> > > On 04/14/2015 12:53 PM, Christoph Hellwig wrote:
> > > > On Sat, Apr 11, 2015 at 09:04:02AM -0400, Jeff Layton wrote:
> > > >> Yuck! How the heck do you clean up the mess if that happens? I
> > > >> guess you're just stuck redoing the copy with normal READ/WRITE?
> > > >>
> > > >> Maybe we need to have the interface return a hard error in that
> > > >> case and not try to give back any sort of offset?
> > > > 
> > > > The NFSv4.2 COPY interface is a train wreck.  At least for Linux I'd
> > > > expect us to simply ignore it and only implement my new CLONE
> > > > operation with sane semantics.  That is unless someone can show some
> > > > real life use case for the inter server copy, in which case we'll
> > > > have to deal with that mess.  But getting that one right at the VFS
> > > > level will be a nightmare anyway.
> > > > 
> > > > Make this a vote from me to not support partial copies and just
> > > > return and error in that case.
> > > 
> > > Agreed.  Looking at the v4.2 spec, COPY does take ca_consecutive and a
> > > ca_synchronous flags that let the client state if the copy should be
> > > done consecutively or synchronously.  I expected to always set
> > > consecutive to "true" for the Linux client.
> > 
> > That's supposed to mean results are well-defined in the partial-copy
> > case, but I think Christoph's suggesting eliminating the partial-copy
> > case entirely?
> > 
> > Which would be fine with me.
> > 
> > It might actually have been me advocating for partial copies.  But that
> > was only because a partial-copy-handling-loop seemed simpler to me than
> > progress callbacks if we were going to support long-running copies.
> > 
> > I'm happy enough not to have it at all.
> 
> Ah, OK, that's great news.
> 
> I thought at one point we were worried about very long running RPCs on
> the server.  Are we not worried about that now?
> 
> Is the client expected to cut the work up into arbitrarily managable
> chunks?  Is the server expected to fail COPY/CLONE requests that it
> thinks would take way too long?  Something else?

Christoph is proposing a CLONE rpc that's required to be atomic:

	https://tools.ietf.org/html/draft-ietf-nfsv4-minorversion2-35#section-15.13
	"The CLONE operation is atomic, that is either all changes or no
	changes are seen by the client or other clients."

So that couldn't be really long-running (or the server is nuts).

So that'd mean Anna would rip out the server-side copy loop and we'd
initially just support btrfs or whatever.

I mean the server-side copy loop may also be useful but I'm all for
wiring up the obvious case first.

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Zach Brown April 14, 2015, 6:54 p.m. UTC | #13
On Tue, Apr 14, 2015 at 02:29:06PM -0400, J. Bruce Fields wrote:
> On Tue, Apr 14, 2015 at 11:22:41AM -0700, Zach Brown wrote:
> > On Tue, Apr 14, 2015 at 02:19:11PM -0400, J. Bruce Fields wrote:
> > > On Tue, Apr 14, 2015 at 01:16:13PM -0400, Anna Schumaker wrote:
> > > > On 04/14/2015 12:53 PM, Christoph Hellwig wrote:
> > > > > On Sat, Apr 11, 2015 at 09:04:02AM -0400, Jeff Layton wrote:
> > > > >> Yuck! How the heck do you clean up the mess if that happens? I
> > > > >> guess you're just stuck redoing the copy with normal READ/WRITE?
> > > > >>
> > > > >> Maybe we need to have the interface return a hard error in that
> > > > >> case and not try to give back any sort of offset?
> > > > > 
> > > > > The NFSv4.2 COPY interface is a train wreck.  At least for Linux I'd
> > > > > expect us to simply ignore it and only implement my new CLONE
> > > > > operation with sane semantics.  That is unless someone can show some
> > > > > real life use case for the inter server copy, in which case we'll
> > > > > have to deal with that mess.  But getting that one right at the VFS
> > > > > level will be a nightmare anyway.
> > > > > 
> > > > > Make this a vote from me to not support partial copies and just
> > > > > return and error in that case.
> > > > 
> > > > Agreed.  Looking at the v4.2 spec, COPY does take ca_consecutive and a
> > > > ca_synchronous flags that let the client state if the copy should be
> > > > done consecutively or synchronously.  I expected to always set
> > > > consecutive to "true" for the Linux client.
> > > 
> > > That's supposed to mean results are well-defined in the partial-copy
> > > case, but I think Christoph's suggesting eliminating the partial-copy
> > > case entirely?
> > > 
> > > Which would be fine with me.
> > > 
> > > It might actually have been me advocating for partial copies.  But that
> > > was only because a partial-copy-handling-loop seemed simpler to me than
> > > progress callbacks if we were going to support long-running copies.
> > > 
> > > I'm happy enough not to have it at all.
> > 
> > Ah, OK, that's great news.
> > 
> > I thought at one point we were worried about very long running RPCs on
> > the server.  Are we not worried about that now?
> > 
> > Is the client expected to cut the work up into arbitrarily managable
> > chunks?  Is the server expected to fail COPY/CLONE requests that it
> > thinks would take way too long?  Something else?
> 
> Christoph is proposing a CLONE rpc that's required to be atomic:
> 
> 	https://tools.ietf.org/html/draft-ietf-nfsv4-minorversion2-35#section-15.13
> 	"The CLONE operation is atomic, that is either all changes or no
> 	changes are seen by the client or other clients."
> 
> So that couldn't be really long-running (or the server is nuts).
> 
> So that'd mean Anna would rip out the server-side copy loop and we'd
> initially just support btrfs or whatever.

Is this relying on btrfs range cloning being atomic?  It certainly
doesn't look atomic.  It can modify items across an arbitrarily large
number of leaf blocks.  It can make the changes across multiple
transactions which could introduce partial modification on reboot after
crashes.  It can fail (the dynamic duo: enomem, eio) and leave the
desintation partially modified.

> I mean the server-side copy loop may also be useful but I'm all for
> wiring up the obvious case first.

Sure, I'm all for wiring up the simple version that doesn't return
partial progress.  If that'll work for you guys.

- z
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Christoph Hellwig April 14, 2015, 7:23 p.m. UTC | #14
On Tue, Apr 14, 2015 at 11:54:08AM -0700, Zach Brown wrote:
> Is this relying on btrfs range cloning being atomic?  It certainly
> doesn't look atomic.  It can modify items across an arbitrarily large
> number of leaf blocks.  It can make the changes across multiple
> transactions which could introduce partial modification on reboot after
> crashes.  It can fail (the dynamic duo: enomem, eio) and leave the
> desintation partially modified.

I didn't mean atomic in the failure atomic sense, but in the sense of
being atomic vs other writes, similar to how Posix specifies it for
writes vs other writes.  Guess I need to express this intent better.
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Zach Brown April 14, 2015, 8:04 p.m. UTC | #15
On Tue, Apr 14, 2015 at 12:23:25PM -0700, Christoph Hellwig wrote:
> On Tue, Apr 14, 2015 at 11:54:08AM -0700, Zach Brown wrote:
> > Is this relying on btrfs range cloning being atomic?  It certainly
> > doesn't look atomic.  It can modify items across an arbitrarily large
> > number of leaf blocks.  It can make the changes across multiple
> > transactions which could introduce partial modification on reboot after
> > crashes.  It can fail (the dynamic duo: enomem, eio) and leave the
> > desintation partially modified.
> 
> I didn't mean atomic in the failure atomic sense, but in the sense of
> being atomic vs other writes, similar to how Posix specifies it for
> writes vs other writes.  Guess I need to express this intent better.

Ah, right, OK.

- z
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diff mbox

Patch

diff --git a/fs/read_write.c b/fs/read_write.c
index 8e1b687..c65ce1d 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -17,6 +17,7 @@ 
 #include <linux/pagemap.h>
 #include <linux/splice.h>
 #include <linux/compat.h>
+#include <linux/mount.h>
 #include "internal.h"
 
 #include <asm/uaccess.h>
@@ -1424,3 +1425,131 @@  COMPAT_SYSCALL_DEFINE4(sendfile64, int, out_fd, int, in_fd,
 	return do_sendfile(out_fd, in_fd, NULL, count, 0);
 }
 #endif
+
+/*
+ * copy_file_range() differs from regular file read and write in that it
+ * specifically allows return partial success.  When it does so is up to
+ * the copy_file_range method.
+ */
+ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
+			    struct file *file_out, loff_t pos_out,
+			    size_t len, int flags)
+{
+	struct inode *inode_in;
+	struct inode *inode_out;
+	ssize_t ret;
+
+	if (flags)
+		return -EINVAL;
+
+	if (len == 0)
+		return 0;
+
+	/* copy_file_range allows full ssize_t len, ignoring MAX_RW_COUNT  */
+	ret = rw_verify_area(READ, file_in, &pos_in, len);
+	if (ret >= 0)
+		ret = rw_verify_area(WRITE, file_out, &pos_out, len);
+	if (ret < 0)
+		return ret;
+
+	if (!(file_in->f_mode & FMODE_READ) ||
+	    !(file_out->f_mode & FMODE_WRITE) ||
+	    (file_out->f_flags & O_APPEND) ||
+	    !file_in->f_op || !file_in->f_op->copy_file_range)
+		return -EINVAL;
+
+	inode_in = file_inode(file_in);
+	inode_out = file_inode(file_out);
+
+	/* make sure offsets don't wrap and the input is inside i_size */
+	if (pos_in + len < pos_in || pos_out + len < pos_out ||
+	    pos_in + len > i_size_read(inode_in))
+		return -EINVAL;
+
+	/* this could be relaxed once a method supports cross-fs copies */
+	if (inode_in->i_sb != inode_out->i_sb ||
+	    file_in->f_path.mnt != file_out->f_path.mnt)
+		return -EXDEV;
+
+	/* forbid ranges in the same file */
+	if (inode_in == inode_out)
+		return -EINVAL;
+
+	ret = mnt_want_write_file(file_out);
+	if (ret)
+		return ret;
+
+	ret = file_in->f_op->copy_file_range(file_in, pos_in, file_out, pos_out,
+					     len, flags);
+	if (ret > 0) {
+		fsnotify_access(file_in);
+		add_rchar(current, ret);
+		fsnotify_modify(file_out);
+		add_wchar(current, ret);
+	}
+	inc_syscr(current);
+	inc_syscw(current);
+
+	mnt_drop_write_file(file_out);
+
+	return ret;
+}
+EXPORT_SYMBOL(vfs_copy_file_range);
+
+SYSCALL_DEFINE6(copy_file_range, int, fd_in, loff_t __user *, off_in,
+		int, fd_out, loff_t __user *, off_out,
+		size_t, len, unsigned int, flags)
+{
+	loff_t pos_in;
+	loff_t pos_out;
+	struct fd f_in;
+	struct fd f_out;
+	ssize_t ret;
+
+	f_in = fdget(fd_in);
+	f_out = fdget(fd_out);
+	if (!f_in.file || !f_out.file) {
+		ret = -EBADF;
+		goto out;
+	}
+
+	ret = -EFAULT;
+	if (off_in) {
+		if (copy_from_user(&pos_in, off_in, sizeof(loff_t)))
+			goto out;
+	} else {
+		pos_in = f_in.file->f_pos;
+	}
+
+	if (off_out) {
+		if (copy_from_user(&pos_out, off_out, sizeof(loff_t)))
+			goto out;
+	} else {
+		pos_out = f_out.file->f_pos;
+	}
+
+	ret = vfs_copy_file_range(f_in.file, pos_in, f_out.file, pos_out, len,
+				  flags);
+	if (ret > 0) {
+		pos_in += ret;
+		pos_out += ret;
+
+		if (off_in) {
+			if (copy_to_user(off_in, &pos_in, sizeof(loff_t)))
+				ret = -EFAULT;
+		} else {
+			f_in.file->f_pos = pos_in;
+		}
+
+		if (off_out) {
+			if (copy_to_user(off_out, &pos_out, sizeof(loff_t)))
+				ret = -EFAULT;
+		} else {
+			f_out.file->f_pos = pos_out;
+		}
+	}
+out:
+	fdput(f_in);
+	fdput(f_out);
+	return ret;
+}
diff --git a/include/linux/fs.h b/include/linux/fs.h
index f4131e8..43a66d45 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1570,6 +1570,7 @@  struct file_operations {
 #ifndef CONFIG_MMU
 	unsigned (*mmap_capabilities)(struct file *);
 #endif
+	ssize_t (*copy_file_range)(struct file *, loff_t, struct file *, loff_t, size_t, int);
 };
 
 struct inode_operations {
@@ -1623,6 +1624,8 @@  extern ssize_t vfs_readv(struct file *, const struct iovec __user *,
 		unsigned long, loff_t *);
 extern ssize_t vfs_writev(struct file *, const struct iovec __user *,
 		unsigned long, loff_t *);
+extern ssize_t vfs_copy_file_range(struct file *, loff_t , struct file *,
+				   loff_t, size_t, int);
 
 struct super_operations {
    	struct inode *(*alloc_inode)(struct super_block *sb);
diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
index e016bd9..2b60f0c 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@ -709,9 +709,11 @@  __SYSCALL(__NR_memfd_create, sys_memfd_create)
 __SYSCALL(__NR_bpf, sys_bpf)
 #define __NR_execveat 281
 __SC_COMP(__NR_execveat, sys_execveat, compat_sys_execveat)
+#define __NR_copy_file_range 282
+__SYSCALL(__NR_copy_file_range, sys_copy_file_range)
 
 #undef __NR_syscalls
-#define __NR_syscalls 282
+#define __NR_syscalls 283
 
 /*
  * All syscalls below here should go away really,
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index 5adcb0a..07f4585 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -159,6 +159,7 @@  cond_syscall(sys_uselib);
 cond_syscall(sys_fadvise64);
 cond_syscall(sys_fadvise64_64);
 cond_syscall(sys_madvise);
+cond_syscall(sys_copy_file_range);
 
 /* arch-specific weak syscall entries */
 cond_syscall(sys_pciconfig_read);