Re: [PATCH v2 1/1] VFS permit cross device vfs_copy_file_range

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Hi folks,

Are there any more comments? Will this be accepted?

On Fri, Jun 30, 2017 at 4:58 PM, Olga Kornievskaia <kolga@xxxxxxxxxx> wrote:
> Allow copy_file_range to copy between different superblocks but only
> of the same file system types.
>
> This feature is needed by NFSv4.2 to perform file copy operation on
> the same server or file copy between different NFSv4.2 servers.
>
> If a file system's fileoperations copy_file_range operation prohibits
> cross-device copies, fall back to do_splice_direct. This would be
> needed for the NFS (destination) server side implementation of the
> file copy and currently for CIFS.
>
> Besides NFS, there is only 1 implementor of the copy_file_range FS
> operation -- CIFS. CIFS assumes incoming file descriptors are both
> CIFS but it will check if they are coming from different servers and
> return error code to fall back to do_splice_direct.
>
> NFS will allow for copies between different NFS servers.
>
> Adding to the vfs.txt documentation to explicitly warn about allowing
> for different superblocks of the same file type to be passed into the
> copy_file_range for the future users of copy_file_range method.
>
> Signed-off-by: Olga Kornievskaia <kolga@xxxxxxxxxx>
> ---
>  Documentation/filesystems/vfs.txt |  7 +++++++
>  fs/read_write.c                   | 13 ++++++-------
>  2 files changed, 13 insertions(+), 7 deletions(-)
>
> diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
> index f42b906..0c243f6 100644
> --- a/Documentation/filesystems/vfs.txt
> +++ b/Documentation/filesystems/vfs.txt
> @@ -845,6 +845,8 @@ 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, unsigned int);
>  };
>
>  Again, all methods are called without any locks being held, unless
> @@ -913,6 +915,11 @@ otherwise noted.
>
>    fallocate: called by the VFS to preallocate blocks or punch a hole.
>
> +  copy_file_range: called by copy_file_range(2) system call. This method
> +                  works on two file descriptors that might reside on
> +                  different superblocks of the same type of file system.
> +
> +
>  Note that the file operations are implemented by the specific
>  filesystem in which the inode resides. When opening a device node
>  (character or block special) most filesystems will call special
> diff --git a/fs/read_write.c b/fs/read_write.c
> index 47c1d44..f981d49 100644
> --- a/fs/read_write.c
> +++ b/fs/read_write.c
> @@ -1589,10 +1589,6 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
>             (file_out->f_flags & O_APPEND))
>                 return -EBADF;
>
> -       /* this could be relaxed once a method supports cross-fs copies */
> -       if (inode_in->i_sb != inode_out->i_sb)
> -               return -EXDEV;
> -
>         if (len == 0)
>                 return 0;
>
> @@ -1602,7 +1598,8 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
>          * Try cloning first, this is supported by more file systems, and
>          * more efficient if both clone and copy are supported (e.g. NFS).
>          */
> -       if (file_in->f_op->clone_file_range) {
> +       if (inode_in->i_sb == inode_out->i_sb &&
> +                       file_in->f_op->clone_file_range) {
>                 ret = file_in->f_op->clone_file_range(file_in, pos_in,
>                                 file_out, pos_out, len);
>                 if (ret == 0) {
> @@ -1611,10 +1608,12 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
>                 }
>         }
>
> -       if (file_out->f_op->copy_file_range) {
> +       if (file_out->f_op->copy_file_range &&
> +                       (file_in->f_op->copy_file_range ==
> +                               file_out->f_op->copy_file_range)) {
>                 ret = file_out->f_op->copy_file_range(file_in, pos_in, file_out,
>                                                       pos_out, len, flags);
> -               if (ret != -EOPNOTSUPP)
> +               if (ret != -EOPNOTSUPP && ret != -EXDEV)
>                         goto done;
>         }
>
> --
> 1.8.3.1
>
> --
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