On Tue, Jul 21, 2020 at 04:31:36PM +0100, Matthew Wilcox wrote:

quoted

Umm, no.  -ENOTBLK is internal - the file systems will retry using
buffered I/O and the error shall never escape to userspace (or even the
VFS for that matter).

Ah, I made the mistake of believing the comments that I could see in
your patch instead of reading the code.

Can I suggest deleting this comment:

        /*
         * No fallback to buffered IO on errors for XFS, direct IO will either
         * complete fully or fail.
         */

and rewording this one:

                /*
                 * Allow a directio write to fall back to a buffered
                 * write *only* in the case that we're doing a reflink
                 * CoW.  In all other directio scenarios we do not
                 * allow an operation to fall back to buffered mode.
                 */

as part of your revised patchset?

That isn't actually true.  In current mainline we only fallback on
reflink RMW cases, but with this series we also fall back for
invalidation failures.