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

[Christoph Hellwig]

On Tue, Nov 11, 2025 at 07:28:20AM +1100, Dave Chinner wrote:
> IOWs, I have no problems with COW filesystems not doing
> preallocation, but if they are going to return success they still
> need to perform all the non-allocation parts of fallocate()
> operations correctly.
> 
> Again, I don't see a need for a new API here to provide
> non-destructive "truncate up only" semantics as we already have
> those semantics built into the ALLOCATE_RANGE operation...

The problem it loses the ability of an intelligent application using
the low-level Linux API to probe what is there.  That might not be a
major issue, but it is an issue at least.