Re: [PATCH v7 15/19] iomap: Support partial direct I/O on user copy failures

On Thu, Sep 9, 2021 at 1:22 PM Christoph Hellwig [off-list ref] wrote:

On Fri, Aug 27, 2021 at 06:49:22PM +0200, Andreas Gruenbacher wrote:

quoted

In iomap_dio_rw, when iomap_apply returns an -EFAULT error and the
IOMAP_DIO_PARTIAL flag is set, complete the request synchronously and
return a partial result.  This allows the caller to deal with the page
fault and retry the remainder of the request.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
---
 fs/iomap/direct-io.c  | 6 ++++++
 include/linux/iomap.h | 7 +++++++
 2 files changed, 13 insertions(+)

diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index 8054f5d6c273..ba88fe51b77a 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c

@@ -561,6 +561,12 @@ __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
              ret = iomap_apply(inode, pos, count, iomap_flags, ops, dio,
                              iomap_dio_actor);
              if (ret <= 0) {
+                     if (ret == -EFAULT && dio->size &&
+                         (dio_flags & IOMAP_DIO_PARTIAL)) {
+                             wait_for_completion = true;
+                             ret = 0;

Do we need a NOWAIT check here to skip the wait_for_completion
for that case?

Hmm, you're probably right, yes. I'll add that.

Thanks,
Andreas