On Tue, Jan 10, 2023 at 01:34:16PM +0000, Matthew Wilcox wrote: > On Tue, Jan 10, 2023 at 12:46:45AM -0800, Christoph Hellwig wrote: > > On Mon, Jan 09, 2023 at 01:46:42PM +0100, Andreas Gruenbacher wrote: > > > We can handle that by adding a new IOMAP_NOCREATE iterator flag and > > > checking for that in iomap_get_folio(). Your patch then turns into > > > the below. > > > > Exactly. And as I already pointed out in reply to Dave's original > > patch what we really should be doing is returning an ERR_PTR from > > __filemap_get_folio instead of reverse-engineering the expected > > error code. > > Ouch, we have a nasty problem. > > If somebody passes FGP_ENTRY, we can return a shadow entry. And the > encodings for shadow entries overlap with the encodings for ERR_PTR, > meaning that some shadow entries will look like errors. The way I > solved this in the XArray code is by shifting the error values by > two bits and encoding errors as XA_ERROR(-ENOMEM) (for example). > > I don't _object_ to introducing XA_ERROR() / xa_err() into the VFS, > but so far we haven't, and I'd like to make that decision intentionally. Sorry, I'm not following this at all -- where in buffered-io.c does anyone pass FGP_ENTRY? Andreas' code doesn't seem to introduce it either...? --D
