[RFC PATCH v3 00/18] Add block device LED trigger

@@ -316,3 +316,12 @@ Description:
 		does not complete in this time then the block driver timeout
 		handler is invoked. That timeout handler can decide to retry
 		the request, to fail it or to start a device recovery strategy.
+
+What:		/sys/block/<disk>/blkdev_leds
+Date:		August 2021
+Contact:	Ian Pilcher <arequipeno@gmail.com>
+Description:
+		Directory containing links to all LEDs that are associated
+		with this block device through the blkdev LED trigger.  Only
+		present when at least one LED is associated.  (See
+		Documentation/leds/ledtrig-blkdev.rst.)

@@ -0,0 +1,48 @@
+What:		/sys/class/leds/<led>/blink_time
+Date:		August 2021
+Contact:	Ian Pilcher <arequipeno@gmail.com>
+Description:
+		Time (in milliseconds) that the LED will be on during a single
+		"blink".
+
+What:		/sys/class/leds/<led>/interval
+Date:		August 2021
+Contact:	Ian Pilcher <arequipeno@gmail.com>
+Description:
+		Frequency (in milliseconds) with which block devices associated
+		with the blkdev LED trigger will be checked for activity.
+
+		NOTE that this attribute is a global setting.  All changes
+		apply to all LEDs associated with the blkdev LED trigger.
+
+What:		/sys/class/leds/<led>/mode
+Date:		August 2021
+Contact:	Ian Pilcher <arequipeno@gmail.com>
+Description:
+		Type of events for which LED will blink - read, write,
+		or rw (both).  Note that any activity that changes the state of
+		the device's non-volatile storage (including discards and cache
+		flushes) is considered to be a write.
+
+What:		/sys/class/leds/<led>/add_blkdev
+Date:		August 2021
+Contact:	Ian Pilcher <arequipeno@gmail.com>
+Description:
+		Associate a block device with this LED by writing its kernel
+		name (as shown in /sys/block) to this attribute.  Multiple
+		device names may be written at once, separated by whitespace.
+
+What:		/sys/class/leds/<led>/delete_blkdev
+Date:		August 2021
+Contact:	Ian Pilcher <arequipeno@gmail.com>
+Description:
+		Remove the association between this LED and a block device by
+		writing the device's kernel name to this attribute.  Multiple
+		device names may be written at once, separated by whitespace.
+
+What:		/sys/class/leds/<led>/block_devices
+Date:		August 2021
+Contact:	Ian Pilcher <arequipeno@gmail.com>
+Description:
+		Directory containing links to all block devices that are
+		associated with this LED.

@@ -10,6 +10,7 @@ LEDs
    leds-class
    leds-class-flash
    leds-class-multicolor
+   ledtrig-blkdev
    ledtrig-oneshot
    ledtrig-transient
    ledtrig-usbport

@@ -0,0 +1,132 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=================================
+Block Device (blkdev) LED Trigger
+=================================
+
+Available when ``CONFIG_LEDS_TRIGGER_BLKDEV=y``.
+
+See also:
+
+* ``Documentation/ABI/testing/sysfs-class-led-trigger-blkdev``
+* ``Documentation/ABI/testing/sysfs-block`` (``/sys/block/<disk>/leds``)
+
+Overview
+========
+
+.. note::
+	The examples below use ``<LED>`` to refer to the name of a
+	system-specific LED.  If no suitable LED is available on a test
+	system (in a virtual machine, for example), it is possible to
+	use a userspace LED (``Documentation/leds/uleds.rst``).
+
+Associate the LED with the ``blkdev`` LED trigger::
+
+	# echo blkdev > /sys/class/leds/<LED>/trigger
+
+	# cat /sys/class/leds/<LED>/trigger
+	... kbd-ctrlrlock [blkdev] disk-activity ...
+
+Note that several new device attributes are available.
+
+* ``add_blkdev`` and ``delete_blkdev`` are used to associate block devices with
+  this LED, and to remove associations.
+
+* ``mode`` is used to control the type of device activity that will cause this
+  LED to blink - read activity, write activity, or both.  (Note that any
+  activity that changes the state of a device's non-volatile storage is
+  considered to be a write.  This includes discard and cache flush requests.)
+
+* ``blink_time`` is the duration (in milliseconds) of each blink of this LED.
+
+* ``interval`` is the frequency (in milliseconds) with which devices are checked
+  for activity.
+
+* The ``block_devices`` directory will contain a symbolic link to every device
+  that is associated with this LED.
+
+Associate the LED with the block device::
+
+	# echo sda > /sys/class/leds/<LED>/add_blkdev
+
+	# ls /sys/class/leds/<LED>/block_devices
+	sda
+
+Reads and write activity on the device should cause the LED to blink.  The
+duration of each blink (in milliseconds) can be adjusted by setting
+``/sys/class/leds/<LED>/blink_on``, and the minimum delay between blinks can
+be set via ``/sys/class/leds/<LED>/blink_off``.
+
+Associate a second device with the LED::
+
+	# echo sdb > /sys/class/leds/<LED>/add_blkdev
+
+	# ls /sys/class/leds/<LED>/block_devices
+	sda  sdb
+
+When a block device is associated with one or more LEDs, the LEDs are linked
+from the device's ``blkdev_leds`` directory::
+
+	# ls /sys/block/sd{a,b}/blkdev_leds
+	/sys/block/sda/blkdev_leds:
+	<LED>
+
+	/sys/block/sdb/blkdev_leds:
+	<LED>
+
+(The ``blkdev_leds`` directory only exists when the block device is associated
+with at least one LED.)
+
+The ``add_blkdev`` and ``delete_blkdev`` attributes both accept multiple,
+whitespace separated, devices.  For example::
+
+	# echo sda sdb > /sys/class/leds/<LED>/delete_blkdev
+
+	# ls /sys/class/leds/<LED>/block_devices
+
+``interval`` and ``blink_time``
+===============================
+
+* The ``interval`` attribute is a global setting.  Changing the value via
+  ``/sys/class/leds/<LED>/interval`` will affect all LEDs associated with
+  the ``blkdev`` LED trigger.
+
+* All associated devices are checked for activity every ``interval``
+  milliseconds, and a blink is triggered on appropriate LEDs.  The duration
+  of an LED's blink is determined by its ``blink_time`` attribute (also in
+  milliseconds).  Thus (assuming that activity of the relevant type has occurred
+  on one of an LED's associated devices), the LED will be on for ``blink_time``
+  milliseconds and off for ``interval - blink_time`` milliseconds.
+
+* The LED subsystem ignores new blink requests for an LED that is currently in
+  in the process of blinking, so setting a ``blink_time`` greater than or equal
+  to ``interval`` will cause some blinks to be dropped.
+
+* Because of processing times, scheduling latencies, etc., avoiding missed
+  blinks actually requires a difference of at least a few milliseconds between
+  the ``blink_time`` and ``interval``.  The required difference is likely to
+  vary from system to system.  As a  reference, a Thecus N5550 NAS requires a
+  difference of 7 milliseconds (``interval == 100``, ``blink_time == 93``).
+
+* The default values (``interval == 100``, ``blink_time == 75``) cause the LED
+  associated with a continuously active device to blink rapidly.  For a more
+  "constantly on" effect, increase the ``blink_time`` (but not too much; see
+  the previous bullet).
+
+Other Notes
+===========
+
+* Many (possibly all) types of block devices work with this trigger, including:
+
+  * SCSI (including SATA and USB) hard disk drives and SSDs
+  * SCSI (including SATA and USB) optical drives
+  * NVMe SSDs
+  * SD cards
+  * loopback block devices (``/dev/loop*``)
+  * device mapper devices, such as LVM logical volumes
+  * MD RAID devices
+  * zRAM compressed RAM-disks
+
+* The ``blkdev`` LED trigger supports many-to-many device/LED associations.
+  A device can be associated with multiple LEDs, and an LED can be associated
+  with multiple devices.

@@ -1362,3 +1362,28 @@ int bdev_read_only(struct block_device *bdev)
 	return bdev->bd_read_only || get_disk_ro(bdev->bd_disk);
 }
 EXPORT_SYMBOL(bdev_read_only);
+
+static int match_disk_name(struct device *const dev, const void *const name)
+{
+	return dev->type == &disk_type
+			&& strcmp(name, dev_to_disk(dev)->disk_name) == 0;
+}
+
+/**
+ * get_disk_by_name - get a gendisk by name
+ * @name:	the name of the disk
+ *
+ * Returns a pointer to the gendisk named @name (if it exists), @NULL if not.
+ * Increments the disk's reference count, so caller must call put_device().
+ */
+struct gendisk *get_disk_by_name(const char *const name)
+{
+	struct device *dev;
+
+	dev = class_find_device(&block_class, NULL, name, match_disk_name);
+	if (dev == NULL)
+		return NULL;
+
+	return dev_to_disk(dev);
+}
+EXPORT_SYMBOL_GPL(get_disk_by_name);

@@ -342,4 +342,14 @@ static inline void printk_all_partitions(void)
 }
 #endif /* CONFIG_BLOCK */
 
+/* for blkdev LED trigger (drivers/leds/trigger/ledtrig-blkdev.c) */
+#ifdef CONFIG_BLOCK
+struct gendisk *get_disk_by_name(const char *name);
+#else
+static inline struct gendisk *get_disk_by_name(const char *name)
+{
+	return NULL;
+}
+#endif
+
 #endif /* _LINUX_GENHD_H */

@@ -0,0 +1,66 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+/*
+ *	Block device LED triggers
+ *
+ *	Copyright 2021 Ian Pilcher <arequipeno@gmail.com>
+ */
+
+#include <linux/leds.h>
+#include <linux/list.h>
+#include <linux/mutex.h>
+
+/* Default blink time & polling interval (milliseconds) */
+#define LEDTRIG_BLKDEV_BLINK_MSEC	75
+#define LEDTRIG_BLKDEV_INTERVAL		100
+
+/* Minimum VALUE for interval or blink_time */
+#define LEDTRIG_BLKDEV_MIN_TIME		25
+
+enum ledtrig_blkdev_mode {
+	LEDTRIG_BLKDEV_MODE_RO	= 0,	/* blink for reads */
+	LEDTRIG_BLKDEV_MODE_WO	= 1,	/* blink for writes */
+	LEDTRIG_BLKDEV_MODE_RW	= 2	/* blink for reads and writes */
+};
+
+/* Trigger-specific info about a block device */
+struct ledtrig_blkdev_disk {
+	struct gendisk		*gd;
+	struct kobject		*dir;
+	struct hlist_head	leds;
+	unsigned long		read_ios;
+	unsigned long		write_ios;
+	unsigned int		generation;
+	bool			read_act;
+	bool			write_act;
+};
+
+/* For many-to-many relationships between "disks" (block devices) and LEDs */
+struct ledtrig_blkdev_link {
+	struct hlist_node		disk_leds_node;
+	struct hlist_node		led_disks_node;
+	struct ledtrig_blkdev_disk	*disk;
+	struct ledtrig_blkdev_led	*led;
+};
+
+/* Every LED associated with the blkdev trigger gets one of these */
+struct ledtrig_blkdev_led {
+	struct kobject			*dir;		/* block_devices dir */
+	struct led_classdev		*led_dev;
+	unsigned int			blink_msec;
+	struct hlist_head		disks;		/* linked block devs */
+	struct hlist_node		leds_node;
+	enum ledtrig_blkdev_mode	mode;
+};
+
+/* All LEDs associated with the trigger */
+static HLIST_HEAD(ledtrig_blkdev_leds);
+
+/* Must hold when changing trigger/LED/device associations */
+static DEFINE_MUTEX(ledtrig_blkdev_mutex);
+
+/* Total number of device-to-LED associations */
+static unsigned int ledtrig_blkdev_count;
+
+/* How often to check for drive activity - in jiffies */
+static unsigned int ledtrig_blkdev_interval;

@@ -6,6 +6,7 @@
  *	Copyright 2021 Ian Pilcher <arequipeno@gmail.com>
  */
 
+#include <linux/ctype.h>
 #include <linux/leds.h>
 #include <linux/list.h>
 #include <linux/mutex.h>

@@ -64,3 +65,76 @@ static unsigned int ledtrig_blkdev_count;
 
 /* How often to check for drive activity - in jiffies */
 static unsigned int ledtrig_blkdev_interval;
+
+
+/*
+ *
+ *	Miscellaneous helper functions
+ *
+ */
+
+/* Like kobject_create_and_add(), but doesn't swallow error codes */
+static struct kobject *blkdev_mkdir(const char *const name,
+				    struct kobject *const parent)
+{
+	struct kobject *dir;
+	int ret;
+
+	dir = kobject_create();
+	if (dir == NULL)
+		return ERR_PTR(-ENOMEM);
+
+	ret = kobject_add(dir, parent, "%s", name);
+	if (ret != 0) {
+		kobject_put(dir);
+		return ERR_PTR(ret);
+	}
+
+	return dir;
+}
+
+/*
+ * Compare a null-terminated C string with a non-null-terminated character
+ * sequence of a known length.  Returns true if equal, false if not.
+ */
+static bool blkdev_streq(const char *const cstr,
+			 const char *const cbuf, const size_t buf_len)
+{
+	return (strlen(cstr) == buf_len) && (memcmp(cstr, cbuf, buf_len) == 0);
+}
+
+/*
+ * Returns a pointer to the first non-whitespace character in s
+ * (or a pointer to the terminating null).
+ */
+static const char *blkdev_skip_space(const char *s)
+{
+	while (*s != 0 && isspace(*s))
+		++s;
+
+	return s;
+}
+
+/*
+ * Returns a pointer to the first whitespace character in s (or a pointer to the
+ * terminating null), which is effectively a pointer to the position *after* the
+ * last character in the non-whitespace token at the beginning of s.  (s is
+ * expected to be the result of a previous call to blkdev_skip_space()).
+ */
+static const char *blkdev_find_space(const char *s)
+{
+	while (*s != 0 && !isspace(*s))
+		++s;
+
+	return s;
+}
+
+static bool blkdev_read_mode(const enum ledtrig_blkdev_mode mode)
+{
+	return mode != LEDTRIG_BLKDEV_MODE_WO;
+}
+
+static bool blkdev_write_mode(const enum ledtrig_blkdev_mode mode)
+{
+	return mode != LEDTRIG_BLKDEV_MODE_RO;
+}

@@ -7,9 +7,11 @@
  */
 
 #include <linux/ctype.h>
+#include <linux/genhd.h>
 #include <linux/leds.h>
 #include <linux/list.h>
 #include <linux/mutex.h>
+#include <linux/part_stat.h>
 
 /* Default blink time & polling interval (milliseconds) */
 #define LEDTRIG_BLKDEV_BLINK_MSEC	75

@@ -66,6 +68,9 @@ static unsigned int ledtrig_blkdev_count;
 /* How often to check for drive activity - in jiffies */
 static unsigned int ledtrig_blkdev_interval;
 
+static void blkdev_process(struct work_struct *const work);
+static DECLARE_DELAYED_WORK(ledtrig_blkdev_work, blkdev_process);
+
 
 /*
  *

@@ -138,3 +143,85 @@ static bool blkdev_write_mode(const enum ledtrig_blkdev_mode mode)
 {
 	return mode != LEDTRIG_BLKDEV_MODE_RO;
 }
+
+
+/*
+ *
+ *	Periodically check for device acitivity and blink LEDs
+ *
+ */
+
+static void blkdev_blink(const struct ledtrig_blkdev_led *const led)
+{
+	unsigned long delay_on = READ_ONCE(led->blink_msec);
+	unsigned long delay_off = 1;	/* 0 leaves LED turned on */
+
+	led_blink_set_oneshot(led->led_dev, &delay_on, &delay_off, 0);
+}
+
+static void blkdev_update_disk(struct ledtrig_blkdev_disk *const disk,
+			       const unsigned int generation)
+{
+	const struct block_device *const part0 = disk->gd->part0;
+	const unsigned long read_ios = part_stat_read(part0, ios[STAT_READ]);
+	const unsigned long write_ios = part_stat_read(part0, ios[STAT_WRITE])
+				+ part_stat_read(part0, ios[STAT_DISCARD])
+				+ part_stat_read(part0, ios[STAT_FLUSH]);
+
+	if (disk->read_ios != read_ios) {
+		disk->read_act = true;
+		disk->read_ios = read_ios;
+	} else {
+		disk->read_act = false;
+	}
+
+	if (disk->write_ios != write_ios) {
+		disk->write_act = true;
+		disk->write_ios = write_ios;
+	} else {
+		disk->write_act = false;
+	}
+
+	disk->generation = generation;
+}
+
+static void blkdev_process(struct work_struct *const work)
+{
+	static unsigned int generation;
+
+	struct ledtrig_blkdev_led *led;
+	struct ledtrig_blkdev_link *link;
+	unsigned long delay;
+
+	if (!mutex_trylock(&ledtrig_blkdev_mutex))
+		goto exit_reschedule;
+
+	hlist_for_each_entry(led, &ledtrig_blkdev_leds, leds_node) {
+
+		hlist_for_each_entry(link, &led->disks, led_disks_node) {
+
+			struct ledtrig_blkdev_disk *const disk = link->disk;
+
+			if (disk->generation != generation)
+				blkdev_update_disk(disk, generation);
+
+			if (disk->read_act && blkdev_read_mode(led->mode)) {
+				blkdev_blink(led);
+				break;
+			}
+
+			if (disk->write_act && blkdev_write_mode(led->mode)) {
+				blkdev_blink(led);
+				break;
+			}
+		}
+	}
+
+	++generation;
+
+	mutex_unlock(&ledtrig_blkdev_mutex);
+
+exit_reschedule:
+	delay = READ_ONCE(ledtrig_blkdev_interval);
+	WARN_ON_ONCE(!schedule_delayed_work(&ledtrig_blkdev_work, delay));
+}

@@ -168,6 +168,9 @@ struct gendisk {
 #endif	/* CONFIG_BLK_DEV_INTEGRITY */
 #if IS_ENABLED(CONFIG_CDROM)
 	struct cdrom_device_info *cdi;
+#endif
+#ifdef CONFIG_LEDS_TRIGGER_BLKDEV
+	struct ledtrig_blkdev_disk *ledtrig;
 #endif
 	int node_id;
 	struct badblocks *bb;

@@ -10,6 +10,7 @@
 
 #include <dt-bindings/leds/common.h>
 #include <linux/device.h>
+#include <linux/genhd.h>
 #include <linux/kernfs.h>
 #include <linux/list.h>
 #include <linux/mutex.h>

@@ -599,4 +600,19 @@ static inline void ledtrig_audio_set(enum led_audio type,
 }
 #endif
 
+#ifdef CONFIG_LEDS_TRIGGER_BLKDEV
+/**
+ * ledtrig_blkdev_disk_init - initialize the ledtrig field of a new gendisk
+ * @gd:	the gendisk to be initialized
+ */
+static inline void ledtrig_blkdev_disk_init(struct gendisk *const gd)
+{
+	gd->ledtrig = NULL;
+}
+#else	/* CONFIG_LEDS_TRIGGER_BLKDEV */
+static inline void ledtrig_blkdev_disk_init(const struct gendisk *gd)
+{
+}
+#endif	/* CONFIG_LEDS_TRIGGER_BLKDEV */
+
 #endif		/* __LINUX_LEDS_H_INCLUDED */

@@ -225,3 +225,59 @@ static void blkdev_process(struct work_struct *const work)
 	delay = READ_ONCE(ledtrig_blkdev_interval);
 	WARN_ON_ONCE(!schedule_delayed_work(&ledtrig_blkdev_work, delay));
 }
+
+
+/*
+ *
+ *	Disassociate a block device from an LED
+ *
+ */
+
+static void blkdev_disk_del_locked(struct ledtrig_blkdev_led *const led,
+				   struct ledtrig_blkdev_link *const link,
+				   struct ledtrig_blkdev_disk *const disk)
+{
+	--ledtrig_blkdev_count;
+
+	if (ledtrig_blkdev_count == 0)
+		WARN_ON(!cancel_delayed_work_sync(&ledtrig_blkdev_work));
+
+	sysfs_remove_link(led->dir, disk->gd->disk_name);
+	sysfs_remove_link(disk->dir, led->led_dev->name);
+	kobject_put(disk->dir);
+
+	hlist_del(&link->led_disks_node);
+	hlist_del(&link->disk_leds_node);
+	kfree(link);
+
+	if (hlist_empty(&disk->leds)) {
+		disk->gd->ledtrig = NULL;
+		kfree(disk);
+	}
+
+	put_device(disk_to_dev(disk->gd));
+}
+
+static void blkdev_disk_delete(struct ledtrig_blkdev_led *const led,
+			       const char *const disk_name,
+			       const size_t name_len)
+{
+	struct ledtrig_blkdev_link *link;
+
+	mutex_lock(&ledtrig_blkdev_mutex);
+
+	hlist_for_each_entry(link, &led->disks, led_disks_node) {
+
+		if (blkdev_streq(link->disk->gd->disk_name,
+						disk_name, name_len)) {
+			blkdev_disk_del_locked(led, link, link->disk);
+			goto exit_unlock;
+		}
+	}
+
+	pr_info("blkdev LED: %.*s not associated with LED %s\n",
+		(int)name_len, disk_name, led->led_dev->name);
+
+exit_unlock:
+	mutex_unlock(&ledtrig_blkdev_mutex);
+}

@@ -281,3 +281,34 @@ static void blkdev_disk_delete(struct ledtrig_blkdev_led *const led,
 exit_unlock:
 	mutex_unlock(&ledtrig_blkdev_mutex);
 }
+
+
+/*
+ *
+ *	Disassociate all LEDs from a block device (because it's going away)
+ *
+ */
+
+/**
+ * ledtrig_blkdev_disk_cleanup - remove a block device from the blkdev LED
+ * trigger
+ * @disk:	the disk to be removed
+ */
+void ledtrig_blkdev_disk_cleanup(struct gendisk *const gd)
+{
+	struct ledtrig_blkdev_link *link;
+	struct hlist_node *next;
+
+	mutex_lock(&ledtrig_blkdev_mutex);
+
+	if (gd->ledtrig != NULL) {
+
+		hlist_for_each_entry_safe(link, next,
+					  &gd->ledtrig->leds, disk_leds_node) {
+			blkdev_disk_del_locked(link->led, link, gd->ledtrig);
+		}
+	}
+
+	mutex_unlock(&ledtrig_blkdev_mutex);
+}
+EXPORT_SYMBOL_GPL(ledtrig_blkdev_disk_cleanup);

@@ -609,10 +609,14 @@ static inline void ledtrig_blkdev_disk_init(struct gendisk *const gd)
 {
 	gd->ledtrig = NULL;
 }
+void ledtrig_blkdev_disk_cleanup(struct gendisk *const gd);
 #else	/* CONFIG_LEDS_TRIGGER_BLKDEV */
 static inline void ledtrig_blkdev_disk_init(const struct gendisk *gd)
 {
 }
+static inline void ledtrig_blkdev_disk_cleanup(const struct gendisk *gd)
+{
+}
 #endif	/* CONFIG_LEDS_TRIGGER_BLKDEV */
 
 #endif		/* __LINUX_LEDS_H_INCLUDED */

@@ -24,6 +24,7 @@
 #include <linux/log2.h>
 #include <linux/pm_runtime.h>
 #include <linux/badblocks.h>
+#include <linux/leds.h>
 
 #include "blk.h"
 

@@ -539,6 +540,7 @@ static void __device_add_disk(struct device *parent, struct gendisk *disk,
 
 	disk_add_events(disk);
 	blk_integrity_add(disk);
+	ledtrig_blkdev_disk_init(disk);
 }
 
 void device_add_disk(struct device *parent, struct gendisk *disk,

@@ -581,6 +583,7 @@ void del_gendisk(struct gendisk *disk)
 	if (WARN_ON_ONCE(!disk->queue))
 		return;
 
+	ledtrig_blkdev_disk_cleanup(disk);
 	blk_integrity_del(disk);
 	disk_del_events(disk);
 

@@ -312,3 +312,171 @@ void ledtrig_blkdev_disk_cleanup(struct gendisk *const gd)
 	mutex_unlock(&ledtrig_blkdev_mutex);
 }
 EXPORT_SYMBOL_GPL(ledtrig_blkdev_disk_cleanup);
+
+
+/*
+ *
+ *	Associate a block device with an LED
+ *
+ */
+
+/* Gets or allocs & initializes the blkdev disk for a gendisk */
+static int blkdev_get_disk(struct gendisk *const gd)
+{
+	struct ledtrig_blkdev_disk *disk;
+	struct kobject *dir;
+
+	if (gd->ledtrig != NULL) {
+		kobject_get(gd->ledtrig->dir);
+		return 0;
+	}
+
+	disk = kmalloc(sizeof(*disk), GFP_KERNEL);
+	if (disk == NULL)
+		return -ENOMEM;
+
+	dir = blkdev_mkdir("blkdev_leds", &disk_to_dev(gd)->kobj);
+	if (IS_ERR(dir)) {
+		kfree(disk);
+		return PTR_ERR(dir);
+	}
+
+	INIT_HLIST_HEAD(&disk->leds);
+	disk->gd = gd;
+	disk->dir = dir;
+	disk->read_ios = 0;
+	disk->write_ios = 0;
+
+	gd->ledtrig = disk;
+
+	return 0;
+}
+
+static void blkdev_put_disk(struct ledtrig_blkdev_disk *const disk)
+{
+	kobject_put(disk->dir);
+
+	if (hlist_empty(&disk->leds)) {
+		disk->gd->ledtrig = NULL;
+		kfree(disk);
+	}
+}
+
+static int blkdev_disk_add_locked(struct ledtrig_blkdev_led *const led,
+				  struct gendisk *const gd)
+{
+	struct ledtrig_blkdev_link *link;
+	struct ledtrig_blkdev_disk *disk;
+	unsigned long delay;
+	int ret;
+
+	link = kmalloc(sizeof(*link), GFP_KERNEL);
+	if (link == NULL) {
+		ret = -ENOMEM;
+		goto error_return;
+	}
+
+	ret = blkdev_get_disk(gd);
+	if (ret != 0)
+		goto error_free_link;
+
+	disk = gd->ledtrig;
+
+	ret = sysfs_create_link(disk->dir, &led->led_dev->dev->kobj,
+				led->led_dev->name);
+	if (ret != 0)
+		goto error_put_disk;
+
+	ret = sysfs_create_link(led->dir, &disk_to_dev(gd)->kobj,
+				gd->disk_name);
+	if (ret != 0)
+		goto error_remove_link;
+
+	link->disk = disk;
+	link->led = led;
+	hlist_add_head(&link->led_disks_node, &led->disks);
+	hlist_add_head(&link->disk_leds_node, &disk->leds);
+
+	if (ledtrig_blkdev_count == 0) {
+		delay = READ_ONCE(ledtrig_blkdev_interval);
+		WARN_ON(!schedule_delayed_work(&ledtrig_blkdev_work, delay));
+	}
+
+	++ledtrig_blkdev_count;
+
+	return 0;
+
+error_remove_link:
+	sysfs_remove_link(disk->dir, led->led_dev->name);
+error_put_disk:
+	blkdev_put_disk(disk);
+error_free_link:
+	kfree(link);
+error_return:
+	return ret;
+}
+
+static bool blkdev_already_linked(const struct ledtrig_blkdev_led *const led,
+				  const struct gendisk *const gd)
+{
+	const struct ledtrig_blkdev_link *link;
+
+	if (gd->ledtrig == NULL)
+		return false;
+
+	hlist_for_each_entry(link, &gd->ledtrig->leds, disk_leds_node) {
+
+		if (link->led == led) {
+			pr_info("blkdev LED: %s already associated with %s\n",
+				gd->disk_name, led->led_dev->name);
+			return true;
+		}
+	}
+
+	return false;
+}
+
+static int blkdev_disk_add(struct ledtrig_blkdev_led *const led,
+			   const char *const disk_name, const size_t name_len)
+{
+	static char name[DISK_NAME_LEN];	/* only used w/ mutex locked */
+	struct gendisk *gd;
+	int ret;
+
+	if (name_len >= DISK_NAME_LEN) {
+		pr_info("blkdev LED: invalid device name %.*s\n",
+			(int)name_len, disk_name);
+		ret = -EINVAL;
+		goto exit_return;
+	}
+
+	ret = mutex_lock_interruptible(&ledtrig_blkdev_mutex);
+	if (ret != 0)
+		goto exit_return;
+
+	memcpy(name, disk_name, name_len);
+	name[name_len] = 0;
+	gd = get_disk_by_name(name);	/* increments disk's refcount */
+
+	if (gd == NULL) {
+		pr_info("blkdev LED: no such block device %.*s\n",
+			(int)name_len, disk_name);
+		ret = -ENODEV;
+		goto exit_unlock;
+	}
+
+	if (blkdev_already_linked(led, gd)) {
+		ret = -EEXIST;
+		goto exit_put_dev;
+	}
+
+	ret = blkdev_disk_add_locked(led, gd);
+
+exit_put_dev:
+	if (ret != 0)
+		put_device(disk_to_dev(gd));
+exit_unlock:
+	mutex_unlock(&ledtrig_blkdev_mutex);
+exit_return:
+	return ret;
+}

@@ -480,3 +480,51 @@ static int blkdev_disk_add(struct ledtrig_blkdev_led *const led,
 exit_return:
 	return ret;
 }
+
+
+/*
+ *
+ *	sysfs attributes to add & delete devices from LEDs
+ *
+ */
+
+static ssize_t blkdev_add_or_del(struct device *const dev,
+				 struct device_attribute *const attr,
+				 const char *const buf, const size_t count);
+
+static struct device_attribute ledtrig_blkdev_attr_add =
+	__ATTR(add_blkdev, 0200, NULL, blkdev_add_or_del);
+
+static struct device_attribute ledtrig_blkdev_attr_del =
+	__ATTR(delete_blkdev, 0200, NULL, blkdev_add_or_del);
+
+static ssize_t blkdev_add_or_del(struct device *const dev,
+				 struct device_attribute *const attr,
+				 const char *const buf, const size_t count)
+{
+	struct ledtrig_blkdev_led *const led = led_trigger_get_drvdata(dev);
+	const char *const disk_name = blkdev_skip_space(buf);
+	const char *const endp = blkdev_find_space(disk_name);
+	const ptrdiff_t name_len = endp - disk_name;	/* always >= 0 */
+	int ret;
+
+	if (name_len == 0) {
+		pr_info("blkdev LED: empty block device name\n");
+		return -EINVAL;
+	}
+
+	if (attr == &ledtrig_blkdev_attr_del) {
+		blkdev_disk_delete(led, disk_name, name_len);
+	} else {	/* attr == &ledtrig_blkdev_attr_add */
+		ret = blkdev_disk_add(led, disk_name, name_len);
+		if (ret != 0)
+			return ret;
+	}
+
+	/*
+	 * Consume everything up to the next non-whitespace token (or the end
+	 * of the input).  Avoids "empty block device name" error if there is
+	 * whitespace after the last token (e.g. a newline).
+	 */
+	return blkdev_skip_space(endp) - buf;
+}

@@ -528,3 +528,66 @@ static ssize_t blkdev_add_or_del(struct device *const dev,
 	 */
 	return blkdev_skip_space(endp) - buf;
 }
+
+
+/*
+ *
+ *	blink_time & interval device attributes
+ *
+ */
+
+static ssize_t blkdev_time_show(struct device *const dev,
+				      struct device_attribute *const attr,
+				      char *const buf);
+
+static ssize_t blkdev_time_store(struct device *const dev,
+				 struct device_attribute *const attr,
+				 const char *const buf, const size_t count);
+
+static struct device_attribute ledtrig_blkdev_attr_blink_time =
+	__ATTR(blink_time, 0644, blkdev_time_show, blkdev_time_store);
+
+static struct device_attribute ledtrig_blkdev_attr_interval =
+	__ATTR(interval, 0644, blkdev_time_show, blkdev_time_store);
+
+static ssize_t blkdev_time_show(struct device *const dev,
+				struct device_attribute *const attr,
+				char *const buf)
+{
+	const struct ledtrig_blkdev_led *const led =
+						led_trigger_get_drvdata(dev);
+	unsigned int value;
+
+	if (attr == &ledtrig_blkdev_attr_blink_time)
+		value = READ_ONCE(led->blink_msec);
+	else	// attr == &ledtrig_blkdev_attr_interval
+		value = jiffies_to_msecs(READ_ONCE(ledtrig_blkdev_interval));
+
+	return sprintf(buf, "%u\n", value);
+}
+
+static ssize_t blkdev_time_store(struct device *const dev,
+				 struct device_attribute *const attr,
+				 const char *const buf, const size_t count)
+{
+	struct ledtrig_blkdev_led *const led = led_trigger_get_drvdata(dev);
+	unsigned int value;
+	int ret;
+
+	ret = kstrtouint(buf, 0, &value);
+	if (ret != 0)
+		return ret;
+
+	if (value < LEDTRIG_BLKDEV_MIN_TIME) {
+		pr_info("blkdev LED: attempt to set time < %s milliseconds\n",
+			__stringify(LEDTRIG_BLKDEV_MIN_TIME));
+		return -ERANGE;
+	}
+
+	if (attr == &ledtrig_blkdev_attr_blink_time)
+		WRITE_ONCE(led->blink_msec, value);
+	else	// attr == &ledtrig_blkdev_attr_interval
+		WRITE_ONCE(ledtrig_blkdev_interval, msecs_to_jiffies(value));
+
+	return count;
+}

@@ -153,4 +153,13 @@ config LEDS_TRIGGER_TTY
 
 	  When build as a module this driver will be called ledtrig-tty.
 
+config LEDS_TRIGGER_BLKDEV
+	bool "LED Trigger for block devices"
+	depends on BLOCK
+	help
+	  The blkdev LED trigger allows LEDs to be controlled by block device
+	  activity (reads and writes).
+
+	  See Documentation/leds/ledtrig-blkdev.rst.
+
 endif # LEDS_TRIGGERS

@@ -16,3 +16,4 @@ obj-$(CONFIG_LEDS_TRIGGER_NETDEV)	+= ledtrig-netdev.o
 obj-$(CONFIG_LEDS_TRIGGER_PATTERN)	+= ledtrig-pattern.o
 obj-$(CONFIG_LEDS_TRIGGER_AUDIO)	+= ledtrig-audio.o
 obj-$(CONFIG_LEDS_TRIGGER_TTY)		+= ledtrig-tty.o
+obj-$(CONFIG_LEDS_TRIGGER_BLKDEV)	+= ledtrig-blkdev.o

@@ -729,3 +729,42 @@ static void blkdev_deactivate(struct led_classdev *const led_dev)
 
 	mutex_unlock(&ledtrig_blkdev_mutex);
 }
+
+
+/*
+ *
+ *	Initialization - register the trigger
+ *
+ */
+
+static struct attribute *ledtrig_blkdev_attrs[] = {
+	&ledtrig_blkdev_attr_add.attr,
+	&ledtrig_blkdev_attr_del.attr,
+	&ledtrig_blkdev_attr_blink_time.attr,
+	&ledtrig_blkdev_attr_interval.attr,
+	&ledtrig_blkdev_attr_mode.attr,
+	NULL
+};
+
+static const struct attribute_group ledtrig_blkdev_attr_group = {
+	.attrs	= ledtrig_blkdev_attrs,
+};
+
+static const struct attribute_group *ledtrig_blkdev_attr_groups[] = {
+	&ledtrig_blkdev_attr_group,
+	NULL
+};
+
+static struct led_trigger ledtrig_blkdev_trigger = {
+	.name		= "blkdev",
+	.activate	= blkdev_activate,
+	.deactivate	= blkdev_deactivate,
+	.groups		= ledtrig_blkdev_attr_groups,
+};
+
+static int __init blkdev_init(void)
+{
+	ledtrig_blkdev_interval = msecs_to_jiffies(LEDTRIG_BLKDEV_INTERVAL);
+	return led_trigger_register(&ledtrig_blkdev_trigger);
+}
+device_initcall(blkdev_init);

@@ -704,3 +704,28 @@ static int blkdev_activate(struct led_classdev *const led_dev)
 exit_return:
 	return ret;
 }
+
+
+/*
+ *
+ *	Disassociate an LED from the trigger
+ *
+ */
+
+static void blkdev_deactivate(struct led_classdev *const led_dev)
+{
+	struct ledtrig_blkdev_led *const led = led_get_trigger_data(led_dev);
+	struct ledtrig_blkdev_link *link;
+	struct hlist_node *next;
+
+	mutex_lock(&ledtrig_blkdev_mutex);
+
+	hlist_for_each_entry_safe(link, next, &led->disks, led_disks_node)
+		blkdev_disk_del_locked(led, link, link->disk);
+
+	hlist_del(&led->leds_node);
+	kobject_put(led->dir);
+	kfree(led);
+
+	mutex_unlock(&ledtrig_blkdev_mutex);
+}

@@ -658,3 +658,49 @@ static ssize_t blkdev_mode_store(struct device *const dev,
 
 static struct device_attribute ledtrig_blkdev_attr_mode =
 	__ATTR(mode, 0644, blkdev_mode_show, blkdev_mode_store);
+
+
+/*
+ *
+ *	Associate an LED with the blkdev trigger
+ *
+ */
+
+static int blkdev_activate(struct led_classdev *const led_dev)
+{
+	struct ledtrig_blkdev_led *led;
+	int ret;
+
+	led = kmalloc(sizeof(*led), GFP_KERNEL);
+	if (led == NULL) {
+		ret = -ENOMEM;
+		goto exit_return;
+	}
+
+	led->led_dev = led_dev;
+	led->blink_msec = LEDTRIG_BLKDEV_BLINK_MSEC;
+	led->mode = LEDTRIG_BLKDEV_MODE_RW;
+	INIT_HLIST_HEAD(&led->disks);
+
+	ret = mutex_lock_interruptible(&ledtrig_blkdev_mutex);
+	if (ret != 0)
+		goto exit_free;
+
+	led->dir = blkdev_mkdir("block_devices", &led_dev->dev->kobj);
+	if (IS_ERR(led->dir)) {
+		ret = PTR_ERR(led->dir);
+		goto exit_unlock;
+	}
+
+	hlist_add_head(&led->leds_node, &ledtrig_blkdev_leds);
+	led_set_trigger_data(led_dev, led);
+	ret = 0;
+
+exit_unlock:
+	mutex_unlock(&ledtrig_blkdev_mutex);
+exit_free:
+	if (ret != 0)
+		kfree(led);
+exit_return:
+	return ret;
+}

@@ -591,3 +591,70 @@ static ssize_t blkdev_time_store(struct device *const dev,
 
 	return count;
 }
+
+
+/*
+ *
+ *	LED mode device attribute
+ *
+ */
+
+static const struct {
+	const char	*name;
+	const char	*show;
+} blkdev_modes[] = {
+	[LEDTRIG_BLKDEV_MODE_RO] = {
+		.name	= "read",
+		.show	= "[read] write rw\n",
+	},
+	[LEDTRIG_BLKDEV_MODE_WO] = {
+		.name	= "write",
+		.show	= "read [write] rw\n",
+	},
+	[LEDTRIG_BLKDEV_MODE_RW] = {
+		.name	= "rw",
+		.show	= "read write [rw]\n",
+	},
+};
+
+static ssize_t blkdev_mode_show(struct device *const dev,
+				struct device_attribute *const attr,
+				char *const buf)
+{
+	const struct ledtrig_blkdev_led *const led =
+					led_trigger_get_drvdata(dev);
+
+	return sprintf(buf, blkdev_modes[READ_ONCE(led->mode)].show);
+}
+
+static ssize_t blkdev_mode_store(struct device *const dev,
+				 struct device_attribute *const attr,
+				 const char *const buf, const size_t count)
+{
+	struct ledtrig_blkdev_led *const led = led_trigger_get_drvdata(dev);
+	const char *const mode_name = blkdev_skip_space(buf);
+	const char *const endp = blkdev_find_space(mode_name);
+	const ptrdiff_t name_len = endp - mode_name;	/* always >= 0 */
+	enum ledtrig_blkdev_mode mode;
+
+	if (name_len == 0) {
+		pr_info("blkdev LED: empty mode\n");
+		return -EINVAL;
+	}
+
+	for (mode = LEDTRIG_BLKDEV_MODE_RO;
+				mode <= LEDTRIG_BLKDEV_MODE_RW; ++mode) {
+
+		if (blkdev_streq(blkdev_modes[mode].name,
+						mode_name, name_len)) {
+			WRITE_ONCE(led->mode, mode);
+			return count;
+		}
+	}
+
+	pr_info("blkdev LED: invalid mode (%.*s)\n", (int)name_len, mode_name);
+	return -EINVAL;
+}
+
+static struct device_attribute ledtrig_blkdev_attr_mode =
+	__ATTR(mode, 0644, blkdev_mode_show, blkdev_mode_store);