Re: [RFC PATCH 17/17] netfs: Combine prepare and issue ops and grab the buffers on request

[Christoph Hellwig]

On Wed, Mar 04, 2026 at 02:51:01PM +0000, David Howells wrote:
> > > +static int cachefiles_query_occupancy(struct netfs_cache_resources *cres,
> > > +				      struct fscache_occupancy *occ)
> > > +{
> > 
> > Independent of fiemap or not, how is this supposed to work?  File
> > systems can create speculative preallocations any time they want,
> > so simply querying for holes vs data will corrupt your cache trivially.
> 
> SEEK_DATA and SEEK_HOLE avoid preallocations, I presume?

No, they can't.  The file system doesn't even know what range is
a persistent preallocation or not.  You need to track your cached
ranges yourself.