[PATCH block v2 3/3] loop: Add support for REQ_NOZERO

[Kirill Tkhai <ktkhai@virtuozzo.com>]

Support for new modifier of REQ_OP_WRITE_ZEROES command.
This results in allocation extents in backing file instead
of actual blocks zeroing.

Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
---
 drivers/block/loop.c |   15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 739b372a5112..f9e5af7b2ee0 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -581,6 +581,15 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd,
 	return 0;
 }
 
+static unsigned int write_zeroes_to_fallocate_mode(unsigned int flags)
+{
+	if (flags & REQ_NOZERO)
+		return 0;
+	if (flags & REQ_NOUNMAP)
+		return FALLOC_FL_ZERO_RANGE;
+	return FALLOC_FL_PUNCH_HOLE;
+}
+
 static int do_req_filebacked(struct loop_device *lo, struct request *rq)
 {
 	struct loop_cmd *cmd = blk_mq_rq_to_pdu(rq);
@@ -604,9 +613,7 @@ static int do_req_filebacked(struct loop_device *lo, struct request *rq)
 		 * write zeroes the range.  Otherwise, punch them out.
 		 */
 		return lo_fallocate(lo, rq, pos,
-			(rq->cmd_flags & REQ_NOUNMAP) ?
-				FALLOC_FL_ZERO_RANGE :
-				FALLOC_FL_PUNCH_HOLE);
+			write_zeroes_to_fallocate_mode(rq->cmd_flags));
 	case REQ_OP_DISCARD:
 		return lo_fallocate(lo, rq, pos, FALLOC_FL_PUNCH_HOLE);
 	case REQ_OP_WRITE:
@@ -877,6 +884,7 @@ static void loop_config_discard(struct loop_device *lo)
 		q->limits.discard_alignment = 0;
 		blk_queue_max_discard_sectors(q, 0);
 		blk_queue_max_write_zeroes_sectors(q, 0);
+		blk_queue_max_allocate_sectors(q, 0);
 		blk_queue_flag_clear(QUEUE_FLAG_DISCARD, q);
 		return;
 	}
@@ -886,6 +894,7 @@ static void loop_config_discard(struct loop_device *lo)
 
 	blk_queue_max_discard_sectors(q, UINT_MAX >> 9);
 	blk_queue_max_write_zeroes_sectors(q, UINT_MAX >> 9);
+	blk_queue_max_allocate_sectors(q, UINT_MAX >> 9);
 	blk_queue_flag_set(QUEUE_FLAG_DISCARD, q);
 }