On Wed, Jun 10, 2020 at 12:59:00PM +1000, Dave Chinner wrote: > [ Please cc the XFS list on XFS and iomap infrastructure changes.] > > On Fri, Jun 05, 2020 at 03:48:35PM -0500, Goldwyn Rodrigues wrote: > > In current scenarios, for XFS, it would mean that a page invalidation > > would end up being a writeback error. So, if iomap returns zero, fall > > back to biffered I/O. XFS has never supported fallback to buffered I/O. > > I hope it is not "never will" ;) > > I wouldn't say "never", but we are not going to change XFS behaviour > because btrfs has a page invalidation vs DIO bug in it... Let me point out a specific "oh shit, I didn't think of that" sort of problem that your blind fallback to buffered IO causes. Do this via direct IO: pwritev2(RWF_NOWAIT) now have it fail invalidation in the direct IO path and fallback to buffered write. What does buffered write do with it? if (iocb->ki_flags & IOCB_NOWAIT) return -EOPNOTSUPP; Yup, userspace gets a completely spurious and bogus -EOPNOTSUPP error to pwritev2() because some 3rd party is accessing the same file via mmap or buffered IO. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx
