Need advice about do we need this if condition

[Valdis Kl=?utf-8?Q?=c4=93?=tnieks]

On Wed, 17 Apr 2019 08:25:22 +0300

(Adding Al Viro and the linux-fsdevel lists, as at the very least, the manpage
for the syscall needs some clarification...)

> hello I am trying to fix https://bugzilla.kernel.org/show_bug.cgi?id=202935

So - convince us that it's in fact a "bug" and not a restriction.

> I found cause
> https://github.com/torvalds/linux/blob/master/fs/cifs/cifsfs.c#L1076 not
> sure is it correct to remove such condition ?

Does the CIFS protocol support copying from a file to another location in the
same file? Was it intended to work on *any* filesystem?

(For that matter, the manpage for the syscall is unclear on whether having both
file descriptors open on the same file is OK or not - for bonus ambiguity
points, there's exactly zero discussion of what happens if source and
destination overlap destructively).