Re: [PATCH][man-pages] sync.2: syncfs() now returns errors if writeback fails

[Eric Biggers]

On Wed, Jun 10, 2020 at 06:33:47AM -0400, Jeff Layton wrote:
> A patch has been merged for v5.8 that changes how syncfs() reports
> errors. Change the sync() manpage accordingly.
> 
> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> ---
>  man2/sync.2 | 24 +++++++++++++++++++++++-
>  1 file changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/man2/sync.2 b/man2/sync.2
> index 7198f3311b05..27e04cff5845 100644
> --- a/man2/sync.2
> +++ b/man2/sync.2
> @@ -86,11 +86,26 @@ to indicate the error.
>  is always successful.
>  .PP
>  .BR syncfs ()
> -can fail for at least the following reason:
> +can fail for at least the following reasons:
>  .TP
>  .B EBADF
>  .I fd
>  is not a valid file descriptor.
> +.TP
> +.B EIO
> +An error occurred during synchronization.
> +This error may relate to data written to any file on the filesystem, or on
> +metadata related to the filesytem itself.
> +.TP
> +.B ENOSPC
> +Disk space was exhausted while synchronizing.
> +.TP
> +.BR ENOSPC ", " EDQUOT
> +Data was written to a files on NFS or another filesystem which does not
> +allocate space at the time of a
> +.BR write (2)
> +system call, and some previous write failed due to insufficient
> +storage space.
>  .SH VERSIONS
>  .BR syncfs ()
>  first appeared in Linux 2.6.39;
> @@ -121,6 +136,13 @@ or
>  .BR syncfs ()
>  provide the same guarantees as fsync called on every file in
>  the system or filesystem respectively.
> +.PP
> +In mainline kernel versions prior to 5.8,
> +.\" commit 735e4ae5ba28c886d249ad04d3c8cc097dad6336
> +.BR syncfs ()
> +will only fail with EBADF when passed a bad file descriptor. In 5.8
> +and later kernels, it will also report an error if one or more inodes failed
> +to be written back since the last syncfs call.

The sentence "In mainline kernel versions prior to 5.8, syncfs() will only fail
with EBADF when passed a bad file descriptor" is ambiguous.  It could mean that
EBADF can now mean other things too.

Maybe write: "In mainline kernel versions prior to 5.8, syncfs() will only fail
when passed a bad file descriptor (EBADF)."

- Eric