From: Andreas Gruenbacher <agruenba@redhat.com>
Date: Thu, 22 Jul 2021 23:59:41 +0000 (+0200)
Subject: iomap: Support partial direct I/O on user copy failures
X-Git-Tag: v5.16-rc1~151^2~4
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=97308f8b0d867e9ef59528cd97f0db55ffdf5651;p=thirdparty%2Fkernel%2Flinux.git

iomap: Support partial direct I/O on user copy failures

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>
---

diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index a2a368e824c03..a434fb7887b28 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -581,6 +581,12 @@ __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
 	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;
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 24f8489583ca7..2a213b0d1e1f5 100644
--- 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);