On Thu, Mar 04, 2021 at 10:38:07AM +0100, Alejandro Colomar wrote:
> Linux 5.12 fixes a regression.
>
> Cross-filesystem (introduced in 5.3) copies were buggy.
>
> Move the statements documenting cross-fs to BUGS.
> Kernels 5.3..5.11 should be patched soon.
>
> State version information for some errors related to this.
>
> Reported-by: Luis Henriques <[email protected]>
> Reported-by: Amir Goldstein <[email protected]>
> Related: <https://lwn.net/Articles/846403/>
> Cc: Greg KH <[email protected]>
> Cc: Michael Kerrisk <[email protected]>
> Cc: Anna Schumaker <[email protected]>
> Cc: Jeff Layton <[email protected]>
> Cc: Steve French <[email protected]>
> Cc: Miklos Szeredi <[email protected]>
> Cc: Trond Myklebust <[email protected]>
> Cc: Alexander Viro <[email protected]>
> Cc: "Darrick J. Wong" <[email protected]>
> Cc: Dave Chinner <[email protected]>
> Cc: Nicolas Boichat <[email protected]>
> Cc: Ian Lance Taylor <[email protected]>
> Cc: Luis Lozano <[email protected]>
> Cc: Andreas Dilger <[email protected]>
> Cc: Olga Kornievskaia <[email protected]>
> Cc: Christoph Hellwig <[email protected]>
> Cc: ceph-devel <[email protected]>
> Cc: linux-kernel <[email protected]>
> Cc: CIFS <[email protected]>
> Cc: samba-technical <[email protected]>
> Cc: linux-fsdevel <[email protected]>
> Cc: Linux NFS Mailing List <[email protected]>
> Cc: Walter Harms <[email protected]>
> Signed-off-by: Alejandro Colomar <[email protected]>
> ---
>
> v3:
> - Don't remove some important text.
> - Reword BUGS.
> v4:
> - Reword.
> - Link to BUGS.
>
> Thanks, Amir, for all the help and better wordings.
>
> Cheers,
>
> Alex
>
> ---
> man2/copy_file_range.2 | 27 +++++++++++++++++++++++----
> 1 file changed, 23 insertions(+), 4 deletions(-)
>
> diff --git a/man2/copy_file_range.2 b/man2/copy_file_range.2
> index 611a39b80..f58bfea8f 100644
> --- a/man2/copy_file_range.2
> +++ b/man2/copy_file_range.2
> @@ -169,6 +169,9 @@ Out of memory.
> .B ENOSPC
> There is not enough space on the target filesystem to complete the copy.
> .TP
> +.BR EOPNOTSUPP " (since Linux 5.12)"
> +The filesystem does not support this operation.
> +.TP
> .B EOVERFLOW
> The requested source or destination range is too large to represent in the
> specified data types.
> @@ -184,10 +187,17 @@ or
> .I fd_out
> refers to an active swap file.
> .TP
> -.B EXDEV
> +.BR EXDEV " (before Linux 5.3)"
> +The files referred to by
> +.IR fd_in " and " fd_out
> +are not on the same filesystem.
> +.TP
> +.BR EXDEV " (since Linux 5.12)"
> The files referred to by
> .IR fd_in " and " fd_out
> -are not on the same mounted filesystem (pre Linux 5.3).
> +are not on the same filesystem,
> +and the source and target filesystems are not of the same type,
> +or do not support cross-filesystem copy.
> .SH VERSIONS
> The
> .BR copy_file_range ()
> @@ -200,8 +210,11 @@ Areas of the API that weren't clearly defined were clarified and the API bounds
> are much more strictly checked than on earlier kernels.
> Applications should target the behaviour and requirements of 5.3 kernels.
> .PP
> -First support for cross-filesystem copies was introduced in Linux 5.3.
> -Older kernels will return -EXDEV when cross-filesystem copies are attempted.
> +Since Linux 5.12,
> +cross-filesystem copies can be achieved
> +when both filesystems are of the same type,
> +and that filesystem implements support for it.
> +See BUGS for behavior prior to 5.12.
> .SH CONFORMING TO
> The
> .BR copy_file_range ()
> @@ -226,6 +239,12 @@ gives filesystems an opportunity to implement "copy acceleration" techniques,
> such as the use of reflinks (i.e., two or more inodes that share
> pointers to the same copy-on-write disk blocks)
> or server-side-copy (in the case of NFS).
> +.SH BUGS
> +In Linux kernels 5.3 to 5.11,
> +cross-filesystem copies were implemented by the kernel,
> +if the operation was not supported by individual filesystems.
> +However, on some virtual filesystems,
> +the call failed to copy, while still reporting success.
...success, or merely a short copy?
(The rest looks reasonable (at least by c_f_r standards) to me.)
--D
> .SH EXAMPLES
> .EX
> #define _GNU_SOURCE
> --
> 2.30.1.721.g45526154a5
>