bug#60455: Missing fallback if copy_file_range returns ENOENT?

[Pádraig Brady]

On 07/01/2023 07:34, Sam James wrote:
> > On 31 Dec 2022, at 18:51, Pádraig Brady <P@draigBrady.com> wrote:
> >
> > On 31/12/2022 17:00, Sam James wrote:
> > > Hi folks,
> > > Originally reported in Gentoo at https://bugs.gentoo.org/885793.
> > > Frank Limpert reported that when copying large files across CIFS shares,
> > > cp may abort because copy_file_range returns ENOENT sometimes.
> > > This sounds like a suspicious kernel bug if CIFS interactions are sometimes
> > > spuriously giving ENOENT, but I'm wondering if coreutils needs to do
> > > anything to handle this as well.
> > > strace output from his cp invocation: 
> > > https://bugs.gentoo.org/attachment.cgi?id=842497
> >
> > We may be able to fallback, but it depends if the errno
> > is possible to be returned at a partial copy or not.
> > If partial then there is not much we can do.
> > Now ENOENT is not a documented errno for copy_file_range()
> > so I'm not sure what we should do with it.
> > I didn't see on the bug above if any data was copied.
> > Could we get more info about that?
>
> Frank got back to me and said an empty file gets created:
> ```
> # cp /mnt/Backup/EAV/data-eav-eav-aktiv-20221207.dump.xz /mnt/OldBackup/EAV/1
> cp: error copying '/mnt/Backup/EAV/data-eav-eav-aktiv-20221207.dump.xz' to 
> '/mnt/OldBackup/EAV/1/data-eav-eav-aktiv-20221207.dump.xz': No such file or 
> directory
> # stat /mnt/OldBackup/EAV/1/data-eav-eav-aktiv-20221207.dump.xz
> File: /mnt/OldBackup/EAV/1/data-eav-eav-aktiv-20221207.dump.xz
> Size: 0 Blocks: 8 IO Block: 1048576 regular empty file

OK then it's probably worth handling in coreutils then.
Note I still get the feeling this is a race in CIFS
that is only being made more apparent with copy_file_range(),
but fair enough that this is a regressions for users and
we should be able to cater for it easy enough.

The attached does that for ENOENT.

cheers,
Pádraig

copy-range-cifs.patch
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