block: add support for limiting gaps in SG lists
Another restriction inherited for NVMe - those devices don't support
SG lists that have "gaps" in them. Gaps refers to cases where the
previous SG entry doesn't end on a page boundary. For NVMe, all SG
entries must start at offset 0 (except the first) and end on a page
boundary (except the last).
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/block/bio.c b/block/bio.c
index 8c2e55e..0ec61c9 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -746,6 +746,14 @@
goto done;
}
+
+ /*
+ * If the queue doesn't support SG gaps and adding this
+ * offset would create a gap, disallow it.
+ */
+ if (q->queue_flags & (1 << QUEUE_FLAG_SG_GAPS) &&
+ bvec_gap_to_prev(prev, offset))
+ return 0;
}
if (bio->bi_vcnt >= bio->bi_max_vecs)
diff --git a/block/blk-merge.c b/block/blk-merge.c
index b3bf0df..5453583 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -568,6 +568,8 @@
bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
{
+ struct request_queue *q = rq->q;
+
if (!rq_mergeable(rq) || !bio_mergeable(bio))
return false;
@@ -591,6 +593,14 @@
!blk_write_same_mergeable(rq->bio, bio))
return false;
+ if (q->queue_flags & (1 << QUEUE_FLAG_SG_GAPS)) {
+ struct bio_vec *bprev;
+
+ bprev = &rq->biotail->bi_io_vec[bio->bi_vcnt - 1];
+ if (bvec_gap_to_prev(bprev, bio->bi_io_vec[0].bv_offset))
+ return false;
+ }
+
return true;
}
diff --git a/include/linux/bio.h b/include/linux/bio.h
index f91decb..d2633ee 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -186,6 +186,15 @@
#define BIOVEC_SEG_BOUNDARY(q, b1, b2) \
__BIO_SEG_BOUNDARY(bvec_to_phys((b1)), bvec_to_phys((b2)) + (b2)->bv_len, queue_segment_boundary((q)))
+/*
+ * Check if adding a bio_vec after bprv with offset would create a gap in
+ * the SG list. Most drivers don't care about this, but some do.
+ */
+static inline bool bvec_gap_to_prev(struct bio_vec *bprv, unsigned int offset)
+{
+ return offset || ((bprv->bv_offset + bprv->bv_len) & (PAGE_SIZE - 1));
+}
+
#define bio_io_error(bio) bio_endio((bio), -EIO)
/*
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 713f8b6..8699bcf 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -512,6 +512,7 @@
#define QUEUE_FLAG_DEAD 19 /* queue tear-down finished */
#define QUEUE_FLAG_INIT_DONE 20 /* queue is initialized */
#define QUEUE_FLAG_NO_SG_MERGE 21 /* don't attempt to merge SG segments*/
+#define QUEUE_FLAG_SG_GAPS 22 /* queue doesn't support SG gaps */
#define QUEUE_FLAG_DEFAULT ((1 << QUEUE_FLAG_IO_STAT) | \
(1 << QUEUE_FLAG_STACKABLE) | \