bug#65599: mv and cp give a pointless warning when moving/copying a directory

[Bruno Haible]

Thanks for looking into this, Paul.

But there's a big misunderstanding. This is not on Android. It's on
Linux with glibc (Ubuntu 22.04, to be precise), as can be seen from the
log file:
  openat(AT_FDCWD, "/lib/x86_64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
and from the fact that I could write to /tmp.

The fchownat() failure comes from the combination of a 'cifs' mount
of the Linux kernel (mount options: 
rw,relatime,vers=1.0,cache=strict,username=bruno,uid=1000,forceuid,gid=1000,forcegid,addr=192.168.**.**,soft,unix,posixpaths,serverino,mapposix,acl,rsize=1048576,wsize=1048576,bsize=1048576,echo_interval=60,actimeo=1,closetimeo=1
 )
and the CIFS/SMB server on my NAS (an old Linux/mips machine).

> Although the attached hacky coreutils patch (which I haven't installed) 
> might solve the immediate problem

Unfortunately, this patch would also silence warnings that are justified
(e.g. when a normal user moves a directory owned by 'root', whose parent
directory has mode drwxrwxrwx). I think the diagnostic should only be
supporessed when, despite the failed fchownat() call, the destination
has the same uid and gid as the 3rd and 4th argument of the fchownat()
invocation.

> it sounds like this is something that Gnulib's fchownat

Whether this is better done in Gnulib or in coreutils/src/copy.c, I can't
judge.

Bruno