netfs: zero the tail of a short DIO/unbuffered readgrafted

The buffered read collector zero-fills the tail of a short read that
stops below the inode's i_size (netfs_clear_unread()), so a read that
races an extending write still returns the expected number of bytes.
The non-buffered collector path does no such thing: it just records
how much was transferred.

Add the same zero-fill for the non-buffered case, gated on
NETFS_SREQ_CLEAR_TAIL: a subreq's source sets that flag when a short
result from it is known to be safe to treat as a hole, as opposed to
NETFS_SREQ_HIT_EOF, which means the read genuinely ran off the end of
the file and should be reported short as-is. Only CLEAR_TAIL should
zero-fill here; a real EOF must stay a real short read.

No source currently sets CLEAR_TAIL on an unbuffered/DIO subrequest,
so this is inert on its own -- a following change teaches cifs to set
it in the one case that needs it.

Fixes: e2d46f2ec332 ("netfs: Change the read result collector to only use one work item")
Reviewed-by: David Howells <dhowells@redhat.com>
Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Cc: Shyam Prasad N <sprasad@microsoft.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Bharath SM <bharathsm@microsoft.com>
Cc: stable@vger.kernel.org

1 files changed, 61 insertions, 0 deletions

diff --git a/drivers/md/dm-pcache/segment.c b/drivers/md/dm-pcache/segment.c
new file mode 100644
index 000000000..8f8816e1c
--- /dev/null
+++ b/drivers/md/dm-pcache/segment.c
@@ -0,0 +1,61 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+#include <linux/dax.h>
+
+#include "pcache_internal.h"
+#include "cache_dev.h"
+#include "segment.h"
+
+int segment_copy_to_bio(struct pcache_segment *segment,
+		u32 data_off, u32 data_len, struct bio *bio, u32 bio_off)
+{
+	struct iov_iter iter;
+	size_t copied;
+	void *src;
+
+	iov_iter_bvec(&iter, ITER_DEST, &bio->bi_io_vec[bio->bi_iter.bi_idx],
+			bio_segments(bio), bio->bi_iter.bi_size);
+	iter.iov_offset = bio->bi_iter.bi_offset;
+	if (bio_off)
+		iov_iter_advance(&iter, bio_off);
+
+	src = segment->data + data_off;
+	copied = _copy_mc_to_iter(src, data_len, &iter);
+	if (copied != data_len)
+		return -EIO;
+
+	return 0;
+}
+
+int segment_copy_from_bio(struct pcache_segment *segment,
+		u32 data_off, u32 data_len, struct bio *bio, u32 bio_off)
+{
+	struct iov_iter iter;
+	size_t copied;
+	void *dst;
+
+	iov_iter_bvec(&iter, ITER_SOURCE, &bio->bi_io_vec[bio->bi_iter.bi_idx],
+			bio_segments(bio), bio->bi_iter.bi_size);
+	iter.iov_offset = bio->bi_iter.bi_offset;
+	if (bio_off)
+		iov_iter_advance(&iter, bio_off);
+
+	dst = segment->data + data_off;
+	copied = _copy_from_iter_flushcache(dst, data_len, &iter);
+	if (copied != data_len)
+		return -EIO;
+	pmem_wmb();
+
+	return 0;
+}
+
+void pcache_segment_init(struct pcache_cache_dev *cache_dev, struct pcache_segment *segment,
+		      struct pcache_segment_init_options *options)
+{
+	segment->seg_info = options->seg_info;
+	segment_info_set_type(segment->seg_info, options->type);
+
+	segment->cache_dev = cache_dev;
+	segment->seg_id = options->seg_id;
+	segment->data_size = PCACHE_SEG_SIZE - options->data_off;
+	segment->data = CACHE_DEV_SEGMENT(cache_dev, options->seg_id) + options->data_off;
+}