On Thu, Apr 20, 2023 at 11:22:31PM +0100, Al Viro wrote: > On Tue, Mar 14, 2023 at 10:07:51PM +0000, David Howells wrote: > > The ITER_PIPE-type iterator was only used for generic_file_splice_read(), > > but that has now been switched to either pull pages directly from the > > pagecache for buffered file splice-reads or to use ITER_BVEC instead for > > O_DIRECT file splice-reads. This leaves ITER_PIPE unused - so remove it. > > Wonderful, except that now you've got duplicates of ->read_iter() for > everyone who wants zero-copy on ->splice_read() ;-/ > > I understand the attraction of arbitrary seeks on those suckers; ITER_PIPE > is a massive headache in that respect. But I really don't like what your > approach trades it for. > > And you are nowhere near done - consider e.g. NFS. Mainline has it > feed ITER_PIPE to nfs_file_read(), which does call generic_file_read_iter() - > after > result = nfs_revalidate_mapping(inode, iocb->ki_filp->f_mapping); > > Sure, you can add nfs_file_splice_read() that would do what nfs_file_read() > does, calling filemap_spice_read() instead of generic_file_read_iter(). > > Repeat the same for ocfs2 (locking of its own). And orangefs. And > XFS (locking, again). And your own AFS, while we are at it. Et sodding > cetera - *everything* that uses generic_file_splice_read() with > ->read_iter other than generic_file_read_iter() needs review and, > quite likely, a ->splice_read() instance of its own. Don't get me wrong - I'd love to kill ITER_PIPE off; it's just that tons of ->splice_read() duplicating the corresponding ->read_iter() up to the point where it would call generic_file_read_iter(), modulo ignoring O_DIRECT case and then calling filemap_splice_read() instead... Painful and asking for trouble down the road.
