scsi: target: tcmu: Implement tmr_notify callback

This patch implements the tmr_notify callback for tcmu.  When the callback
is called, tcmu checks the list of aborted commands it received as
parameter:

 - aborted commands in the qfull_queue are removed from the queue and
   target_complete_command is called

 - from the cmd_ids of aborted commands currently uncompleted in cmd ring
   it creates a list of aborted cmd_ids.

Finally a TMR notification is written to cmd ring containing TMR type and
cmd_id list. If there is no space in ring, the TMR notification is queued
on a TMR specific queue.

The TMR specific queue 'tmr_queue' can be seen as a extension of the cmd
ring. At the end of each iexecution of tcmu_complete_commands() we check
whether tmr_queue contains TMRs and try to move them onto the ring. If
tmr_queue is not empty after that, we don't call run_qfull_queue() because
commands must not overtake TMRs.

This way we guarantee that cmd_ids in TMR notification received by
userspace either match an active, not yet completed command or are no
longer valid due to userspace having complete some cmd_ids meanwhile.

New commands that were assigned to an aborted cmd_id will always appear on
the cmd ring _after_ the TMR.

Link: https://lore.kernel.org/r/20200726153510.13077-8-bstroesser@ts.fujitsu.comReviewed-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Bodo Stroesser <bstroesser@ts.fujitsu.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

include/uapi/linux/target_core_user.h

@@ -45,6 +45,7 @@
 #define ALIGN_SIZE 64 /* Should be enough for most CPUs */
 #define TCMU_MAILBOX_FLAG_CAP_OOOC (1 << 0) /* Out-of-order completions */
 #define TCMU_MAILBOX_FLAG_CAP_READ_LEN (1 << 1) /* Read data length */
+#define TCMU_MAILBOX_FLAG_CAP_TMR (1 << 2) /* TMR notifications */
 
 struct tcmu_mailbox {
 	__u16 version;
@@ -62,6 +63,7 @@ struct tcmu_mailbox {
 enum tcmu_opcode {
 	TCMU_OP_PAD = 0,
 	TCMU_OP_CMD,
+	TCMU_OP_TMR,
 };
 
 /*
@@ -128,6 +130,29 @@ struct tcmu_cmd_entry {
 
 } __packed;
 
+struct tcmu_tmr_entry {
+	struct tcmu_cmd_entry_hdr hdr;
+
+#define TCMU_TMR_UNKNOWN		0
+#define TCMU_TMR_ABORT_TASK		1
+#define TCMU_TMR_ABORT_TASK_SET		2
+#define TCMU_TMR_CLEAR_ACA		3
+#define TCMU_TMR_CLEAR_TASK_SET		4
+#define TCMU_TMR_LUN_RESET		5
+#define TCMU_TMR_TARGET_WARM_RESET	6
+#define TCMU_TMR_TARGET_COLD_RESET	7
+/* Pseudo reset due to received PR OUT */
+#define TCMU_TMR_LUN_RESET_PRO		128
+	__u8 tmr_type;
+
+	__u8 __pad1;
+	__u16 __pad2;
+	__u32 cmd_cnt;
+	__u64 __pad3;
+	__u64 __pad4;
+	__u16 cmd_ids[0];
+} __packed;
+
 #define TCMU_OP_ALIGN_SIZE sizeof(__u64)
 
 enum tcmu_genl_cmd {