[RFC PATCH V2 3/6] ublk_drv: define macros for recovery feature and check them

[ZiyangZhang <ZiyangZhang@linux.alibaba.com>]

Define some macros for recovery feature. Especially define a new state:
UBLK_S_DEV_RECOVERING which implies the ublk_device is recovering.

UBLK_F_USER_RECOVERY implies that:
(1) ublk_drv enables recovery feature. It won't let monitor_work to
    automatically abort rqs and release the device. Instead, it waits
	for user's START_USER_RECOVERY ctrl-cmd.

(2) In monitor_work after a crash, ublk_drv ends(aborts) rqs issued to
    userspace(ublksrv) before crash.

(3) In task work and ublk_queue_rq() after a crash, ublk_drv requeues
    rqs dispatched after crash.

UBLK_F_USER_RECOVERY_REISSUE implies that:
(1) everything UBLK_F_USER_RECOVERY implies except
(2) ublk_drv requeues rqs issued to userspace(ublksrv) before crash.

UBLK_F_USER_RECOVERY_REISSUE is designed for backends which:
(1) tolerate double-writes because we may issue the same rq twice.
(2) cannot let frontend users get I/O error, such as a RDONLY system.

Signed-off-by: ZiyangZhang <ZiyangZhang@linux.alibaba.com>
---
 drivers/block/ublk_drv.c      | 31 ++++++++++++++++++++++++++++++-
 include/uapi/linux/ublk_cmd.h |  7 +++++++
 2 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index 0c6db0978ed0..0c3d32e8d686 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -49,7 +49,9 @@
 /* All UBLK_F_* have to be included into UBLK_F_ALL */
 #define UBLK_F_ALL (UBLK_F_SUPPORT_ZERO_COPY \
 		| UBLK_F_URING_CMD_COMP_IN_TASK \
-		| UBLK_F_NEED_GET_DATA)
+		| UBLK_F_NEED_GET_DATA \
+		| 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)
@@ -323,6 +325,33 @@ static inline int ublk_queue_cmd_buf_size(struct ublk_device *ub, int q_id)
 			PAGE_SIZE);
 }
 
+/*
+ * TODO: UBLK_F_USER_RECOVERY should be a flag for device, not for queue,
+ * since "some queues are aborted while others are recoverd" is really weird.
+ */
+static inline bool ublk_can_use_recovery(struct ublk_device *ub)
+{
+	struct ublk_queue *ubq = ublk_get_queue(ub, 0);
+
+	if (ubq->flags & UBLK_F_USER_RECOVERY)
+		return true;
+	return false;
+}
+
+/*
+ * TODO: UBLK_F_USER_RECOVERY_REISSUE should be a flag for device, not for queue,
+ * since "some queues are aborted while others are recoverd" is really weird.
+ */
+static inline bool ublk_can_use_recovery_reissue(struct ublk_device *ub)
+{
+	struct ublk_queue *ubq = ublk_get_queue(ub, 0);
+
+	if ((ubq->flags & UBLK_F_USER_RECOVERY) &&
+			(ubq->flags & UBLK_F_USER_RECOVERY_REISSUE))
+		return true;
+	return false;
+}
+
 static void ublk_free_disk(struct gendisk *disk)
 {
 	struct ublk_device *ub = disk->private_data;
diff --git a/include/uapi/linux/ublk_cmd.h b/include/uapi/linux/ublk_cmd.h
index 677edaab2b66..7f7e6f44cec5 100644
--- a/include/uapi/linux/ublk_cmd.h
+++ b/include/uapi/linux/ublk_cmd.h
@@ -17,6 +17,8 @@
 #define	UBLK_CMD_STOP_DEV	0x07
 #define	UBLK_CMD_SET_PARAMS	0x08
 #define	UBLK_CMD_GET_PARAMS	0x09
+#define	UBLK_CMD_START_USER_RECOVERY	0x10
+#define UBLK_CMD_END_USER_RECOVERY	0x11
 
 /*
  * IO commands, issued by ublk server, and handled by ublk driver.
@@ -74,9 +76,14 @@
  */
 #define UBLK_F_NEED_GET_DATA (1UL << 2)
 
+#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
+#define UBLK_S_DEV_RECOVERING	2
 
 /* shipped via sqe->cmd of io_uring command */
 struct ublksrv_ctrl_cmd {
-- 
2.27.0