Re: [PATCH v6 5/7] xfs: Support atomic write for statx

[Christoph Hellwig]

On Mon, Sep 30, 2024 at 09:37:16AM -0700, Darrick J. Wong wrote:
> Ok, so we're only supporting untorn writes if they're exactly the fs
> blocksize, and 1 fsblock is between awu_min/max.  That simplifies a lot
> of things. :)
> 
> Not supporting sub-fsblock atomic writes means that we'll never hit the
> directio COW fallback code, which uses the pagecache.
> 
> Not supporting multi-fsblock atomic writes means that you don't have to
> figure out how to ensure that we always do cow on forcealign
> granularity.  Though as I pointed out elsewhere in this thread, that's a
> forcealign problem.

It does simplify things a lot, and is probably a good idea for
the initial version.  But I suspect support for atomic writes
smaller than the block size will be really useful and we should
eventually support them, but maybe now on reflinked files or
alwayscow.