[PATCH V4 6/8] ublk_drv: support UBLK_F_USER_RECOVERY_REISSUE

[ZiyangZhang]

UBLK_F_USER_RECOVERY_REISSUE implies that:
With a dying ubq_daemon, ublk_drv let monitor_work requeues rq issued to
userspace(ublksrv) before the ubq_daemon is dying.

UBLK_F_USER_RECOVERY_REISSUE is designed for backends which:
(1) tolerate double-write since ublk_drv may issue the same rq
    twice.
(2) does not let frontend users get I/O error, such as read-only FS
    and VM backend.

Signed-off-by: ZiyangZhang <ZiyangZhang@xxxxxxxxxxxxxxxxx>
---
 drivers/block/ublk_drv.c      | 17 +++++++++++++++--
 include/uapi/linux/ublk_cmd.h |  2 ++
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index 9610afe11463..dc33ebc20c01 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -50,7 +50,8 @@
 #define UBLK_F_ALL (UBLK_F_SUPPORT_ZERO_COPY \
 		| UBLK_F_URING_CMD_COMP_IN_TASK \
 		| UBLK_F_NEED_GET_DATA \
-		| UBLK_F_USER_RECOVERY)
+		| UBLK_F_USER_RECOVERY \
+		| UBLK_F_USER_RECOVERY_REISSUE)
 
 /* All UBLK_PARAM_TYPE_* should be included here */
 #define UBLK_PARAM_TYPE_ALL (UBLK_PARAM_TYPE_BASIC | UBLK_PARAM_TYPE_DISCARD)
@@ -325,6 +326,15 @@ static inline int ublk_queue_cmd_buf_size(struct ublk_device *ub, int q_id)
 			PAGE_SIZE);
 }
 
+static inline bool ublk_queue_can_use_recovery_reissue(
+		struct ublk_queue *ubq)
+{
+	if ((ubq->flags & UBLK_F_USER_RECOVERY) &&
+			(ubq->flags & UBLK_F_USER_RECOVERY_REISSUE))
+		return true;
+	return false;
+}
+
 static inline bool ublk_queue_can_use_recovery(
 		struct ublk_queue *ubq)
 {
@@ -641,7 +651,10 @@ static void __ublk_fail_req(struct ublk_queue *ubq, struct ublk_io *io,
 				req->tag,
 				io->flags);
 		io->flags |= UBLK_IO_FLAG_ABORTED;
-		blk_mq_end_request(req, BLK_STS_IOERR);
+		if (ublk_queue_can_use_recovery_reissue(ubq))
+			blk_mq_requeue_request(req, false);
+		else
+			blk_mq_end_request(req, BLK_STS_IOERR);
 	}
 }
 
diff --git a/include/uapi/linux/ublk_cmd.h b/include/uapi/linux/ublk_cmd.h
index 340ff14bde49..332370628757 100644
--- a/include/uapi/linux/ublk_cmd.h
+++ b/include/uapi/linux/ublk_cmd.h
@@ -76,6 +76,8 @@
 
 #define UBLK_F_USER_RECOVERY	(1UL << 3)
 
+#define UBLK_F_USER_RECOVERY_REISSUE	(1UL << 4)
+
 /* device state */
 #define UBLK_S_DEV_DEAD	0
 #define UBLK_S_DEV_LIVE	1
-- 
2.27.0