[PATCH 5.15 25/33] iomap: Support partial direct I/O on user copy failures

Greg Kroah-Hartman
2022-04-29T10:45:45Z

From: Andreas Gruenbacher <agruenba@redhat.com>

commit 97308f8b0d867e9ef59528cd97f0db55ffdf5651 upstream

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>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/iomap/direct-io.c | 6 ++++++
include/linux/iomap.h | 7 +++++++
2 files changed, 13 insertions(+)

--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -581,6 +581,12 @@ __iomap_dio_rw(struct kiocb *iocb, struc
if (iov_iter_rw(iter) == READ && iomi.pos >= dio->i_size)
iov_iter_revert(iter, iomi.pos - dio->i_size);

+ if (ret == -EFAULT && dio->size && (dio_flags & IOMAP_DIO_PARTIAL)) {
+ if (!(iocb->ki_flags & IOCB_NOWAIT))
+ wait_for_completion = true;
+ ret = 0;
+ }
+
/* magic error code to fall back to buffered I/O */
if (ret == -ENOTBLK) {
wait_for_completion = true;
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -330,6 +330,13 @@ struct iomap_dio_ops {
*/
#define IOMAP_DIO_OVERWRITE_ONLY (1 << 1)

+/*
+ * When a page fault occurs, return a partial synchronous result and allow
+ * the caller to retry the rest of the operation after dealing with the page
+ * fault.
+ */
+#define IOMAP_DIO_PARTIAL (1 << 2)
+
ssize_t iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
const struct iomap_ops *ops, const struct iomap_dio_ops *dops,
unsigned int dio_flags);