[RFC PATCH v2 04/10] block: Add functions to set & clear block device LEDs

[Ian Pilcher <arequipeno@gmail.com>]

Create a symlink from /sys/class/leds/<LED>/block_devices to each block
device that is associated with that LED

Ensure device LED is cleared when device is removed

Signed-off-by: Ian Pilcher <arequipeno@gmail.com>
---
 block/blk-ledtrig.c | 93 +++++++++++++++++++++++++++++++++++++++++++++
 block/blk-ledtrig.h |  3 ++
 block/genhd.c       |  1 +
 3 files changed, 97 insertions(+)

diff --git a/block/blk-ledtrig.c b/block/blk-ledtrig.c
index c5ad57ed9c3b..280fa9edc2dd 100644
--- a/block/blk-ledtrig.c
+++ b/block/blk-ledtrig.c
@@ -6,9 +6,13 @@
  *	Copyright 2021 Ian Pilcher <arequipeno@gmail.com>
  */
 
+#include <linux/genhd.h>
 #include <linux/leds.h>
 #include <linux/mutex.h>
 
+#include "blk-ledtrig.h"
+
+
 /*
  *
  *	Trigger mutex and LED list
@@ -46,3 +50,92 @@ static struct blk_ledtrig_led *blk_ledtrig_find(const char *const led_name,
 
 	return NULL;
 }
+
+
+/*
+ *
+ *	Clear a block device's LED
+ *
+ */
+
+// Also called from blk_ledtrig_dev_set()
+static void blk_ledtrig_dev_cleanup(struct gendisk *const disk,
+				    struct blk_ledtrig_led *const old_led)
+{
+	sysfs_remove_link(old_led->dir, disk->disk_name);
+	list_del(&disk->led_dev_list_node);
+}
+
+// Also called from blk_ledtrig_deactivate()
+static void blk_ledtrig_dev_clear_locked(struct gendisk *const disk,
+					 struct blk_ledtrig_led *const old_led)
+{
+	RCU_INIT_POINTER(disk->led, NULL);
+	if (old_led != NULL)
+		blk_ledtrig_dev_cleanup(disk, old_led);
+}
+
+// Also called from genhd.c:del_gendisk()
+void blk_ledtrig_dev_clear(struct gendisk *const disk)
+{
+	struct blk_ledtrig_led *old_led;
+
+	mutex_lock(&blk_ledtrig_mutex);
+	old_led = rcu_dereference_protected(disk->led,
+					lockdep_is_held(&blk_ledtrig_mutex));
+	blk_ledtrig_dev_clear_locked(disk, old_led);
+	mutex_unlock(&blk_ledtrig_mutex);
+}
+
+
+/*
+ *
+ *	Set a block device's LED
+ *
+ */
+
+static int blk_ledtrig_dev_set(struct gendisk *const disk,
+			       const char *const led_name,
+			       const size_t name_len)
+{
+	struct blk_ledtrig_led *new_led, *old_led;
+	int ret;
+
+	ret = mutex_lock_interruptible(&blk_ledtrig_mutex);
+	if (ret != 0)
+		goto led_set_exit_return;
+
+	new_led = blk_ledtrig_find(led_name, name_len);
+	if (new_led == NULL) {
+		pr_info("no LED named %.*s associated with blkdev trigger\n",
+			(int)name_len, led_name);
+		ret = -ENODEV;
+		goto led_set_exit_unlock;
+	}
+
+	old_led = rcu_dereference_protected(disk->led,
+					lockdep_is_held(&blk_ledtrig_mutex));
+
+	if (old_led == new_led) {
+		ret = 0;
+		goto led_set_exit_unlock;
+	}
+
+	ret = sysfs_create_link(new_led->dir, &disk_to_dev(disk)->kobj,
+				disk->disk_name);
+	if (ret != 0)
+		goto led_set_exit_unlock;
+
+	if (old_led != NULL)
+		blk_ledtrig_dev_cleanup(disk, old_led);
+
+	rcu_assign_pointer(disk->led, new_led);
+	list_add(&disk->led_dev_list_node, &new_led->dev_list);
+
+	ret = 0;
+
+led_set_exit_unlock:
+	mutex_unlock(&blk_ledtrig_mutex);
+led_set_exit_return:
+	return ret;
+}
diff --git a/block/blk-ledtrig.h b/block/blk-ledtrig.h
index 95a79d2fe447..66a1302a4174 100644
--- a/block/blk-ledtrig.h
+++ b/block/blk-ledtrig.h
@@ -16,9 +16,12 @@ static inline void blk_ledtrig_disk_init(struct gendisk *const disk)
 	RCU_INIT_POINTER(disk->led, NULL);
 }
 
+void blk_ledtrig_dev_clear(struct gendisk *const disk);
+
 #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) {}
 
 #endif	// CONFIG_BLK_LED_TRIGGERS
 
diff --git a/block/genhd.c b/block/genhd.c
index b168172e664b..9fa734aeab0f 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -583,6 +583,7 @@ void del_gendisk(struct gendisk *disk)
 	if (WARN_ON_ONCE(!disk->queue))
 		return;
 
+	blk_ledtrig_dev_clear(disk);
 	blk_integrity_del(disk);
 	disk_del_events(disk);
 
-- 
2.31.1