[RFC PATCH v2 09/10] block: Blink device LED (if any) when request is sent to its driver

[Ian Pilcher <arequipeno@xxxxxxxxx>]

Call led_blink_set_oneshot() in RCU critical section to ensure that LED
doesn't disappear.  (See synchronize_rcu() call in blk_ledtrig_deactivate()).

Signed-off-by: Ian Pilcher <arequipeno@xxxxxxxxx>
---
 block/blk-ledtrig.c | 26 ++++++++++++++++++++++++++
 block/blk-ledtrig.h |  9 +++++++++
 block/blk-mq.c      |  2 ++
 3 files changed, 37 insertions(+)

diff --git a/block/blk-ledtrig.c b/block/blk-ledtrig.c
index 14b1d33a2953..10588f3dea15 100644
--- a/block/blk-ledtrig.c
+++ b/block/blk-ledtrig.c
@@ -6,6 +6,7 @@
  *	Copyright 2021 Ian Pilcher <arequipeno@xxxxxxxxx>
  */
 
+#include <linux/blkdev.h>
 #include <linux/ctype.h>
 #include <linux/genhd.h>
 #include <linux/leds.h>
@@ -441,3 +442,28 @@ static int __init blk_ledtrig_init(void)
 	return led_trigger_register(&blk_ledtrig_trigger);
 }
 device_initcall(blk_ledtrig_init);
+
+
+/*
+ *
+ *	Blink the LED associated with a (non-NULL) disk (if set)
+ *
+ */
+
+void __blk_ledtrig_try_blink(struct request *const rq)
+{
+	struct blk_ledtrig_led *bd_led;
+	unsigned long delay_on, delay_off;
+
+	rcu_read_lock();
+
+	bd_led = rcu_dereference(rq->rq_disk->led);
+
+	if (bd_led != NULL) {
+		delay_on = READ_ONCE(bd_led->blink_on);
+		delay_off = READ_ONCE(bd_led->blink_off);
+		led_blink_set_oneshot(bd_led->led, &delay_on, &delay_off, 0);
+	}
+
+	rcu_read_unlock();
+}
diff --git a/block/blk-ledtrig.h b/block/blk-ledtrig.h
index 771000d43647..7eb1d88e2b3c 100644
--- a/block/blk-ledtrig.h
+++ b/block/blk-ledtrig.h
@@ -26,10 +26,19 @@ ssize_t blk_ledtrig_dev_led_show(struct device *const dev,
 				 struct device_attribute *const attr,
 				 char *const buf);
 
+void __blk_ledtrig_try_blink(struct request *const rq);
+
+static inline void blk_ledtrig_try_blink(struct request *const rq)
+{
+	if (rq->rq_disk != NULL)
+		__blk_ledtrig_try_blink(rq);
+}
+
 #else	// CONFIG_BLK_LED_TRIGGERS
 
 static inline void blk_ledtrig_disk_init(const struct gendisk *disk) {}
 static inline void blk_ledtrig_dev_clear(const struct gendisk *disk) {}
+static inline void blk_ledtrig_try_blink(const struct request *rq) {}
 
 #endif	// CONFIG_BLK_LED_TRIGGERS
 
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 2c4ac51e54eb..7732e31f3ca8 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -40,6 +40,7 @@
 #include "blk-stat.h"
 #include "blk-mq-sched.h"
 #include "blk-rq-qos.h"
+#include "blk-ledtrig.h"
 
 static DEFINE_PER_CPU(struct llist_head, blk_cpu_done);
 
@@ -1381,6 +1382,7 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
 		switch (ret) {
 		case BLK_STS_OK:
 			queued++;
+			blk_ledtrig_try_blink(rq);
 			break;
 		case BLK_STS_RESOURCE:
 		case BLK_STS_DEV_RESOURCE:
-- 
2.31.1