[RFC] xfs: fake fallocate success for always CoW inodes

[Florian Weimer]

* Hans Holmberg:

> We don't support preallocations for CoW inodes and we currently fail
> with -EOPNOTSUPP, but this causes an issue for users of glibc's
> posix_fallocate[1]. If fallocate fails, posix_fallocate falls back on
> writing actual data into the range to try to allocate blocks that way.
> That does not actually gurantee anything for CoW inodes however as we
> write out of place.

Why doesn't fallocate trigger the copy instead?  Isn't this what the
user is requesting?

Thanks,
Florian