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)