[PATCH v3 3/3] leds: trigger: Add block device LED trigger

[Ian Pilcher]

Add LEDS_TRIGGER_BLKDEV (tristate) config option to control building of
the trigger.

Signed-off-by: Ian Pilcher <arequipeno@xxxxxxxxx>
---
 drivers/leds/trigger/Kconfig          |   9 +
 drivers/leds/trigger/Makefile         |   1 +
 drivers/leds/trigger/ledtrig-blkdev.c | 889 ++++++++++++++++++++++++++
 3 files changed, 899 insertions(+)
 create mode 100644 drivers/leds/trigger/ledtrig-blkdev.c

diff --git a/drivers/leds/trigger/Kconfig b/drivers/leds/trigger/Kconfig
index 1f1d57288085..219d15c046d7 100644
--- a/drivers/leds/trigger/Kconfig
+++ b/drivers/leds/trigger/Kconfig
@@ -153,4 +153,13 @@ config LEDS_TRIGGER_TTY
 
 	  When build as a module this driver will be called ledtrig-tty.
 
+config LEDS_TRIGGER_BLKDEV
+	tristate "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
diff --git a/drivers/leds/trigger/Makefile b/drivers/leds/trigger/Makefile
index 25c4db97cdd4..d53bab5d93f1 100644
--- a/drivers/leds/trigger/Makefile
+++ b/drivers/leds/trigger/Makefile
@@ -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
diff --git a/drivers/leds/trigger/ledtrig-blkdev.c b/drivers/leds/trigger/ledtrig-blkdev.c
new file mode 100644
index 000000000000..4b7b17a91949
--- /dev/null
+++ b/drivers/leds/trigger/ledtrig-blkdev.c
@@ -0,0 +1,889 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+/*
+ *	Block device LED trigger
+ *
+ *	Copyright 2021 Ian Pilcher <arequipeno@xxxxxxxxx>
+ */
+
+#include <linux/genhd.h>
+#include <linux/leds.h>
+#include <linux/module.h>
+#include <linux/part_stat.h>
+
+/* Default blink time & check interval (milliseconds) */
+#define LED_BDEV_BLINK_MSEC	75
+#define LED_BDEV_INTERVAL	100
+
+/* Minimum blink time & check interval (milliseconds) */
+#define LED_BDEV_MIN_BLINK	10
+#define LED_BDEV_MIN_INT	25
+
+/* Device activity type that will make LED blink */
+enum led_bdev_mode {
+	LED_BDEV_MODE_RO	= 0,
+	LED_BDEV_MODE_WO	= 1,
+	LED_BDEV_MODE_RW	= 2
+};
+
+/* Block device information (BDI) - 1 per blkdev linked to at least 1 LED */
+struct led_bdev_bdi {
+	struct block_device	*bdev;
+	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 block devices and LEDs */
+struct led_bdev_link {
+	struct hlist_node	bdi_leds_node;
+	struct hlist_node	led_bdis_node;
+	struct led_bdev_bdi	*bdi;
+	struct led_bdev_led	*led;
+};
+
+/* Every LED associated with the led_bdev trigger gets one of these */
+struct led_bdev_led {
+	struct led_classdev	*led_cdev;
+	unsigned int		blink_msec;
+	struct hlist_head	bdis;
+	struct hlist_node	leds_node;
+	enum led_bdev_mode	mode;
+};
+
+/* Forward declarations to make this file compile in a reasonable order */
+static void led_bdev_process(struct work_struct *work);
+static struct led_bdev_bdi *led_bdev_get_bdi(const char *name);
+static int led_bdev_link(struct led_bdev_led *led, struct led_bdev_bdi *bdi);
+static void led_bdev_put_bdi(struct led_bdev_bdi *bdi);
+static void led_bdev_bdi_release(struct device *dev, void *res);
+static void led_bdev_unlink(struct led_bdev_led *led,
+			    struct led_bdev_link *link,
+			    struct led_bdev_bdi *bdi, bool releasing);
+static bool led_bdev_process_link(const struct led_bdev_led *led,
+				  const struct led_bdev_link *link,
+				  unsigned int generation);
+
+/* Protects everything except atomic sysfs attributes */
+static DEFINE_MUTEX(led_bdev_mutex);
+
+/* All LEDs associated with the trigger */
+static HLIST_HEAD(led_bdev_leds);
+
+/* Class for "global" trigger attributes (interval) */
+static struct class *led_bdev_class;
+
+/* How often to check for drive activity - in jiffies */
+static unsigned int led_bdev_interval;
+
+/* Delayed work to periodically check for activity & blink LEDs */
+static DECLARE_DELAYED_WORK(led_bdev_work, led_bdev_process);
+
+/* Total number of device-to-LED associations (links) */
+static unsigned int led_bdev_link_count;
+
+/* Empty attribute list for the linked_leds & linked_devices "groups" */
+static struct attribute *led_bdev_attrs_empty[] = { NULL };
+
+/* linked_leds sysfs directory for block devs linked to 1 or more LEDs */
+static const struct attribute_group led_bdev_linked_leds = {
+	.name	= "linked_leds",
+	.attrs	= led_bdev_attrs_empty,
+};
+
+/* linked_devices sysfs directory for each LED associated with the trigger */
+static const struct attribute_group led_bdev_linked_devs = {
+	.name	= "linked_devices",
+	.attrs	= led_bdev_attrs_empty,
+};
+
+/**
+ * led_bdev_activate() - Called when an LED is associated with the trigger.
+ * @led_cdev:	The LED
+ *
+ * Allocates & initializes the @led_bdev_led structure and adds it to the
+ * @led_bdev_leds list.
+ *
+ * Context:	Process context.  Takes and releases @led_bdev_mutex.
+ * Return:	``0`` on success, ``-errno`` on error.
+ */
+static int led_bdev_activate(struct led_classdev *const led_cdev)
+{
+	struct led_bdev_led *led;
+	int ret;
+
+	led = kmalloc(sizeof(*led), GFP_KERNEL);
+	if (led == NULL) {
+		ret = -ENOMEM;
+		goto exit_return;
+	}
+
+	led->led_cdev = led_cdev;
+	led->blink_msec = LED_BDEV_BLINK_MSEC;
+	led->mode = LED_BDEV_MODE_RW;
+	INIT_HLIST_HEAD(&led->bdis);
+
+	ret = mutex_lock_interruptible(&led_bdev_mutex);
+	if (ret != 0)
+		goto exit_free;
+
+	hlist_add_head(&led->leds_node, &led_bdev_leds);
+	led_set_trigger_data(led_cdev, led);
+
+	mutex_unlock(&led_bdev_mutex);
+
+exit_free:
+	if (ret != 0)
+		kfree(led);
+exit_return:
+	return ret;
+}
+
+/**
+ * link_device_store() - ``link_device`` device attribute store function.
+ * @dev:	The LED device
+ * @attr:	The ``link_device`` attribute (@dev_attr_link_device)
+ * @buf:	The name of the block device (as written to sysfs attribute)
+ * @count:	The number of bytes written to the attribute
+ *
+ * Block device name is written to the attribute to "link" the block device
+ * to the LED.  LED will blink to show activity on any of its linked blocked
+ * devices.
+ *
+ *   * Calls led_bdev_get_bdi() to find or create the BDI for the device.
+ *   * Checks that device isn't already linked to this LED.
+ *   * Calls led_bdev_link() to create the link.
+ *
+ * Context:	Process context.  Takes and releases @led_bdev_mutex.
+ * Return:	@count on success, ``-errno`` on error.
+ */
+static ssize_t link_device_store(struct device *const dev,
+				 struct device_attribute *const attr,
+				 const char *const buf, const size_t count)
+{
+	struct led_bdev_led *const led = led_trigger_get_drvdata(dev);
+	const struct led_bdev_link *link;
+	struct led_bdev_bdi *bdi;
+	int ret;
+
+	ret = mutex_lock_interruptible(&led_bdev_mutex);
+	if (ret != 0)
+		goto exit_return;
+
+	bdi = led_bdev_get_bdi(buf);
+	if (IS_ERR(bdi)) {
+		ret = PTR_ERR(bdi);
+		goto exit_unlock;
+	}
+
+	hlist_for_each_entry(link, &bdi->leds, bdi_leds_node) {
+		if (link->led == led) {
+			ret = -EEXIST;
+			goto exit_put_bdi;
+		}
+	}
+
+	ret = led_bdev_link(led, bdi);
+
+exit_put_bdi:
+	if (ret != 0)
+		led_bdev_put_bdi(bdi);
+exit_unlock:
+	mutex_unlock(&led_bdev_mutex);
+exit_return:
+	return (ret == 0) ? count : ret;
+}
+
+/**
+ * led_bdev_get_bdi() - Find or create the BDI for a block device.
+ * @name:	The name of the block device
+ *
+ * If the device already has a BDI (because it is already linked to an LED),
+ * simply return the existing BDI.
+ *
+ * Otherwise, allocate a new BDI (as a device resource), create the block
+ * device's ``linked_leds`` directory (attribute group), and add the BDI
+ * resource to the block device.
+ *
+ * Context:	Process context.  Caller must hold @led_bdev_mutex.
+ * Return:	Pointer to the BDI, error pointer on error.
+ */
+static struct led_bdev_bdi *led_bdev_get_bdi(const char *const name)
+{
+	struct led_bdev_bdi *bdi;
+	struct device *dev;
+	int ret;
+
+	dev = class_find_device_by_name(&block_class, name);
+	if (dev == NULL) {
+		ret = -ENODEV;
+		goto exit_return;
+	}
+
+	bdi = devres_find(dev, led_bdev_bdi_release, NULL, NULL);
+	if (bdi != NULL) {
+		ret = 0;
+		goto exit_put_dev;
+	}
+
+	bdi = devres_alloc(led_bdev_bdi_release, sizeof(*bdi), GFP_KERNEL);
+	if (bdi == NULL) {
+		ret = -ENOMEM;
+		goto exit_put_dev;
+	}
+
+	ret = sysfs_create_group(&dev->kobj, &led_bdev_linked_leds);
+	if (ret != 0)
+		goto exit_free_bdi;
+
+	INIT_HLIST_HEAD(&bdi->leds);
+	bdi->bdev = dev_to_bdev(dev);
+	bdi->read_ios = 0;
+	bdi->write_ios = 0;
+
+	devres_add(dev, bdi);
+
+exit_free_bdi:
+	if (ret != 0)
+		devres_free(bdi);
+exit_put_dev:
+	put_device(dev);	/* Allow the device to be released */
+exit_return:
+	return (ret == 0) ? bdi : ERR_PTR(ret);
+}
+
+/**
+ * led_bdev_link() - "Link" a block device to an LED.
+ * @led:	The LED
+ * @bdi:	The block device
+ *
+ * Called from link_device_store() to create the link between an LED and a
+ * block device.
+ *
+ *   * Allocates & initializes link structure.
+ *   * Adds block device symlink to LED's ``linked_devices`` directory.
+ *   * Adds LED symlink to block devices's ``linked_leds`` directory.
+ *   * Adds link to LED's list of block devices and device's list of LEDs.
+ *
+ * If the new link is the only one (i.e. no other block device/LED links
+ * already exist), schedule delayed work to periodically check for block
+ * device activity and blink LEDs.
+ *
+ * Context:	Process context.  Caller must hold @led_bdev_mutex.
+ * Return:	0 on success, ``-errno`` on error.
+ */
+static int led_bdev_link(struct led_bdev_led *const led,
+			 struct led_bdev_bdi *const bdi)
+{
+	struct led_bdev_link *link;
+	unsigned long delay;
+	int ret;
+
+	link = kmalloc(sizeof(*link), GFP_KERNEL);
+	if (link == NULL) {
+		ret = -ENOMEM;
+		goto error_return;
+	}
+
+	ret = sysfs_add_link_to_group(bdev_kobj(bdi->bdev),
+				      led_bdev_linked_leds.name,
+				      &led->led_cdev->dev->kobj,
+				      led->led_cdev->name);
+	if (ret != 0)
+		goto error_free_link;
+
+	ret = sysfs_add_link_to_group(&led->led_cdev->dev->kobj,
+				      led_bdev_linked_devs.name,
+				      bdev_kobj(bdi->bdev),
+				      dev_name(&bdi->bdev->bd_device));
+	if (ret != 0)
+		goto error_remove_symlink;
+
+	link->bdi = bdi;
+	link->led = led;
+	hlist_add_head(&link->led_bdis_node, &led->bdis);
+	hlist_add_head(&link->bdi_leds_node, &bdi->leds);
+
+	if (led_bdev_link_count == 0) {
+		delay = READ_ONCE(led_bdev_interval);
+		WARN_ON(!schedule_delayed_work(&led_bdev_work, delay));
+	}
+
+	++led_bdev_link_count;
+
+	return 0;
+
+error_remove_symlink:
+	sysfs_remove_link_from_group(bdev_kobj(bdi->bdev),
+				     led_bdev_linked_leds.name,
+				     led->led_cdev->name);
+error_free_link:
+	kfree(link);
+error_return:
+	return ret;
+}
+
+/**
+ * unlink_device_store() - ``unlink_device`` device attribute store function.
+ * @dev:	The LED device
+ * @attr:	The ``unlink_device`` attribute (@dev_attr_unlink_device)
+ * @buf:	The name of the block device (as written to the sysfs attribute)
+ * @count:	The number of bytes written to the attribute
+ *
+ * Block device name is written to the attribute to "unlink" the block device
+ * from the LED.  I.e. the LED will no longer blink to show activity on that
+ * block device.
+ *
+ *   * Finds block device (BDI) in LED's list of linked devices.
+ *   * Calls led_bdev_unlink() to destroy the link.
+ *
+ * Context:	Process context.  Takes and releases @led_bdev_mutex.
+ * Return:	@count on success, ``-errno`` on error.
+ */
+static ssize_t unlink_device_store(struct device *const dev,
+				   struct device_attribute *const attr,
+				   const char *const buf, const size_t count)
+{
+	struct led_bdev_led *const led = led_trigger_get_drvdata(dev);
+	struct led_bdev_link *link;
+	int ret;
+
+	ret = mutex_lock_interruptible(&led_bdev_mutex);
+	if (ret != 0)
+		return ret;
+
+	hlist_for_each_entry(link, &led->bdis, led_bdis_node) {
+
+		if (sysfs_streq(dev_name(&link->bdi->bdev->bd_device), buf)) {
+			led_bdev_unlink(led, link, link->bdi, false);
+			break;
+		}
+	}
+
+	mutex_unlock(&led_bdev_mutex);
+
+	return count;
+}
+
+/**
+ * led_bdev_unlink() - "Unlink" a block device from an LED.
+ * @led:	The LED
+ * @link:	The existing link between the LED and the block device
+ * @bdi:	The block device
+ * @releasing:	Indicates whether the BDI is being released (because the
+ *		block device has been removed)
+ *
+ * Removes and frees the link between an LED and a block device.
+ *
+ *   * Removes the link from the LED's list of block devices and the
+ *     device's list of LEDs.
+ *   * Frees the link structure.
+ *   * Removes the block device symlink from the LED's ``linked_devices``
+ *     directory.
+ *
+ * If the block device is **not** being released:
+ *
+ *   * Removes the LED symlink from the block device's ``linked_leds``
+ *     directory.
+ *   * Calls led_bdev_put_bdi() to clean up the BDI, if required.
+ *
+ * If the removed link was the only one (i.e. there are no existing block
+ * device/LED links after its removal), cancel the periodic delayed work
+ * which checks for device activity.
+ *
+ * Called from multiple locations:
+ *
+ *   * unlink_device_store() - requested via ``unlink_device`` sysfs attribute
+ *     (@releasing == ``false``)
+ *   * led_bdev_deactivate() - unlink a block device from an LED that is no
+ *     longer associated with the trigger (@releasing == ``false``)
+ *   * led_bdev_bdi_release() - unlink an LED from a block device that has
+ *     been removed (@releasing == ``true``)
+ *
+ * Context:	Process context.  Caller must hold @led_bdev_mutex.
+ */
+static void led_bdev_unlink(struct led_bdev_led *const led,
+			    struct led_bdev_link *const link,
+			    struct led_bdev_bdi *const bdi,
+			    const bool releasing)
+{
+	--led_bdev_link_count;
+
+	if (led_bdev_link_count == 0)
+		WARN_ON(!cancel_delayed_work_sync(&led_bdev_work));
+
+	hlist_del(&link->led_bdis_node);
+	hlist_del(&link->bdi_leds_node);
+	kfree(link);
+
+	sysfs_remove_link_from_group(&led->led_cdev->dev->kobj,
+				     led_bdev_linked_devs.name,
+				     dev_name(&bdi->bdev->bd_device));
+
+	/*
+	 * If the BDI is being released, the device's attribute groups have
+	 * already been removed, and the BDI will be freed automatically.
+	 */
+	if (!releasing) {
+
+		sysfs_remove_link_from_group(bdev_kobj(bdi->bdev),
+					     led_bdev_linked_leds.name,
+					     led->led_cdev->name);
+		led_bdev_put_bdi(bdi);
+	}
+}
+
+/**
+ * led_bdev_put_bdi() - Remove and free a BDI, if it is no longer needed.
+ * @bdi:	The BDI
+ *
+ * Does nothing if the BDI (block device) is still linked to at least one LED.
+ *
+ * If the BDI is no longer linked to any LEDs:
+ *
+ *   * Removes the block device's ``linked_leds`` directory (attribute group).
+ *   * Removes the BDI from the block device and frees it.
+ *
+ * Called from led_bdev_unlink() (and in link_device_store() error path).
+ *
+ * Context:	Process context.  Caller must hold @led_bdev_mutex.
+ */
+static void led_bdev_put_bdi(struct led_bdev_bdi *const bdi)
+{
+	struct block_device *const bdev = bdi->bdev;
+	int ret;
+
+	if (hlist_empty(&bdi->leds)) {
+
+		sysfs_remove_group(bdev_kobj(bdev), &led_bdev_linked_leds);
+		ret = devres_destroy(&bdev->bd_device, led_bdev_bdi_release,
+				     NULL, NULL);
+		WARN_ON(ret != 0);
+	}
+}
+
+/**
+ * led_bdev_deactivate() - Called when an LED is disassociated from the
+ *			   trigger.
+ * @led_cdev:	The LED
+ *
+ * Calls led_bdev_unlink() for each block device linked to the LED, removes
+ * the LED from the @led_bdev_leds list, and frees the @led_bdev_led structure.
+ *
+ * Context:	Process context.  Takes and releases @led_bdev_mutex.
+ */
+static void led_bdev_deactivate(struct led_classdev *const led_cdev)
+{
+	struct led_bdev_led *const led = led_get_trigger_data(led_cdev);
+	struct led_bdev_link *link;
+	struct hlist_node *next;
+
+	mutex_lock(&led_bdev_mutex);
+
+	hlist_for_each_entry_safe(link, next, &led->bdis, led_bdis_node)
+		led_bdev_unlink(led, link, link->bdi, false);
+
+	hlist_del(&led->leds_node);
+	kfree(led);
+
+	mutex_unlock(&led_bdev_mutex);
+}
+
+/**
+ * led_bdev_bdi_release() - BDI device resource release function.
+ * @dev:	The block device
+ * @res:	The BDI
+ *
+ * Called when the block device with which a BDI is associated has been
+ * removed.  Calls led_bdev_unlink() for each LED linked to the block device.
+ *
+ * Context:	Process context.  Takes and releases @led_bdev_mutex.
+ */
+static void led_bdev_bdi_release(struct device *const dev, void *const res)
+{
+	struct led_bdev_bdi *const bdi = res;
+	struct led_bdev_link *link;
+	struct hlist_node *next;
+
+	mutex_lock(&led_bdev_mutex);
+
+	hlist_for_each_entry_safe(link, next, &bdi->leds, bdi_leds_node)
+		led_bdev_unlink(link->led, link, bdi, true);
+
+	mutex_unlock(&led_bdev_mutex);
+}
+
+/**
+ * led_bdev_process() - Check linked devices for activity and blink LEDs.
+ * @work:	Delayed work (@led_bdev_work)
+ *
+ * Iterates through block devices linked to LEDs and calls
+ * led_bdev_process_link() to check the device and (if appropriate) blink
+ * the LED.
+ *
+ *   * If led_bdev_process_link() blinks an LED (returns ``true``), there is
+ *     no need to check more devices associated with that LED.
+ *   * A block device can be linked to multiple LEDs, so we use a "generation"
+ *     that is incremented each time this function is called to ensure that
+ *     we only check a block device once per call to this function.
+ *
+ * When finished, schedules itself to run again after @led_bdev_interval
+ * jiffies.
+ *
+ * Context:	Process context.  Takes and releases @led_bdev_mutex.
+ */
+static void led_bdev_process(struct work_struct *const work)
+{
+	static unsigned int generation;
+
+	struct led_bdev_led *led;
+	struct led_bdev_link *link;
+	unsigned long delay;
+
+	if (!mutex_trylock(&led_bdev_mutex))
+		goto exit_reschedule;
+
+	hlist_for_each_entry(led, &led_bdev_leds, leds_node) {
+
+		hlist_for_each_entry(link, &led->bdis, led_bdis_node) {
+
+			if (led_bdev_process_link(led, link, generation))
+				break;
+		}
+	}
+
+	++generation;
+
+	mutex_unlock(&led_bdev_mutex);
+
+exit_reschedule:
+	delay = READ_ONCE(led_bdev_interval);
+	WARN_ON_ONCE(!schedule_delayed_work(&led_bdev_work, delay));
+}
+
+/**
+ * led_bdev_process_link() - Check a linked block device for activity and blink
+ *			     the linked LED if appropriate.
+ * @led:	The LED
+ * @link:	The link
+ * @generation:	Identifies when the linked BDI was last updated
+ *
+ * Updates BDI's activity counters if BDI's generation doesn't match the
+ * current value.  Blinks LED if the correct type of activity (based on
+ * the LED's @mode) has occurred since the last check.
+ *
+ * Context:	Process context.  Caller must hold @led_bdev_mutex.
+ * Return:	``true`` if the LED was blinked, ``false`` if not.
+ */
+static bool led_bdev_process_link(const struct led_bdev_led *const led,
+				  const struct led_bdev_link *const link,
+				  const unsigned int generation)
+{
+	struct led_bdev_bdi *const bdi = link->bdi;
+
+	/*
+	 * If this block device is linked to multiple LEDs, it may have already
+	 * been processed in this "generation".  No need to update its activity
+	 * counters in that case.
+	 */
+	if (bdi->generation != generation) {
+
+		unsigned long read_ios, write_ios;
+
+		read_ios = part_stat_read(bdi->bdev, ios[STAT_READ]);
+
+		write_ios = part_stat_read(bdi->bdev, ios[STAT_WRITE])
+				+ part_stat_read(bdi->bdev, ios[STAT_DISCARD])
+				+ part_stat_read(bdi->bdev, ios[STAT_FLUSH]);
+
+		if (bdi->read_ios != read_ios) {
+			bdi->read_act = true;
+			bdi->read_ios = read_ios;
+		} else {
+			bdi->read_act = false;
+		}
+
+		if (bdi->write_ios != write_ios) {
+			bdi->write_act = true;
+			bdi->write_ios = write_ios;
+		} else {
+			bdi->write_act = false;
+		}
+
+		bdi->generation = generation;
+	}
+
+	if ((bdi->read_act && led->mode != LED_BDEV_MODE_WO)
+			|| (bdi->write_act && led->mode != LED_BDEV_MODE_RO)) {
+
+		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_cdev, &delay_on, &delay_off, 0);
+		return true;
+	}
+
+	return false;
+}
+
+/**
+ * blink_time_show() - ``blink_time`` device attribute show function.
+ * @dev:	The LED device
+ * @attr:	The ``blink_time`` attribute (@dev_attr_blink_time)
+ * @buf:	Output buffer
+ *
+ * Writes the current value of the LED's @blink_msec to @buf.
+ *
+ * Context:	Process context.
+ * Return:	The number of characters written to @buf.
+ */
+static ssize_t blink_time_show(struct device *const dev,
+			       struct device_attribute *const attr,
+			       char *const buf)
+{
+	const struct led_bdev_led *const led = led_trigger_get_drvdata(dev);
+
+	return sprintf(buf, "%u\n", READ_ONCE(led->blink_msec));
+}
+
+/**
+ * blink_time_store() - ``blink_time`` device attribute store function.
+ * @dev:	The LED device
+ * @attr:	The ``blink_time`` attribute (@dev_attr_blink_time)
+ * @buf:	The new value (as written to the sysfs attribute)
+ * @count:	The number of bytes written to the attribute
+ *
+ * Sets the LED's @blink_msec (the duration in milliseconds of one blink).
+ *
+ * Context:	Process context.
+ * Return:	@count on success, ``-errno`` on error.
+ */
+static ssize_t blink_time_store(struct device *const dev,
+				struct device_attribute *const attr,
+				const char *const buf, const size_t count)
+{
+	struct led_bdev_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 < LED_BDEV_MIN_BLINK)
+		return -ERANGE;
+
+	WRITE_ONCE(led->blink_msec, value);
+	return count;
+}
+
+/* Data for mode_show() & mode_store() */
+static const struct {
+	char	name[sizeof("write")];			/* longest name */
+	char	show[sizeof("[read] write rw\n")];	/* all the same size */
+} led_bdev_modes[] = {
+	[LED_BDEV_MODE_RO] = {
+		.name	= "read",
+		.show	= "[read] write rw\n",
+	},
+	[LED_BDEV_MODE_WO] = {
+		.name	= "write",
+		.show	= "read [write] rw\n",
+	},
+	[LED_BDEV_MODE_RW] = {
+		.name	= "rw",
+		.show	= "read write [rw]\n",
+	},
+};
+
+/**
+ * mode_show() - ``mode`` device attribute show function.
+ * @dev:	The LED device
+ * @attr:	The ``mode`` attribute (@dev_attr_mode)
+ * @buf:	Output buffer
+ *
+ * Writes the current value of the LED's @mode to @buf.
+ *
+ * Context:	Process context.
+ * Return:	The number of characters written to @buf.
+ */
+static ssize_t mode_show(struct device *const dev,
+			 struct device_attribute *const attr, char *const buf)
+{
+	const struct led_bdev_led *const led = led_trigger_get_drvdata(dev);
+
+	return sprintf(buf, led_bdev_modes[READ_ONCE(led->mode)].show);
+}
+
+/**
+ * mode_store() - ``mode`` device attribute store function.
+ * @dev:	The LED device
+ * @attr:	The ``mode`` attribute (@dev_attr_mode)
+ * @buf:	The new value (as written to the sysfs attribute)
+ * @count:	The number of bytes written to the attribute
+ *
+ * Sets the LED's @mode (``read``, ``write``, or ``rw``).
+ *
+ * Context:	Process context.
+ * Return:	@count on success, ``-errno`` on error.
+ */
+static ssize_t mode_store(struct device *const dev,
+			  struct device_attribute *const attr,
+			  const char *const buf, const size_t count)
+{
+	struct led_bdev_led *const led = led_trigger_get_drvdata(dev);
+	enum led_bdev_mode mode;
+
+	for (mode = LED_BDEV_MODE_RO; mode <= LED_BDEV_MODE_RW; ++mode) {
+
+		if (sysfs_streq(led_bdev_modes[mode].name, buf)) {
+			WRITE_ONCE(led->mode, mode);
+			return count;
+		}
+	}
+
+	return -EINVAL;
+}
+
+/**
+ * interval_show() - ``interval`` class attribute show function.
+ * @class:	The ``ledtrig_blkdev`` class (@led_bdev_class)
+ * @attr:	The ``interval`` attribute (@class_attr_interval)
+ * @buf:	Output buffer
+ *
+ * Writes the current value of @led_bdev_interval to @buf.
+ *
+ * Context:	Process context.
+ * Return:	The number of characters written to @buf.
+ */
+static ssize_t interval_show(struct class *const class,
+			     struct class_attribute *const attr,
+			     char *const buf)
+{
+	return sprintf(buf, "%u\n",
+		       jiffies_to_msecs(READ_ONCE(led_bdev_interval)));
+}
+
+/**
+ * interval_store() - ``interval`` class attribute store function
+ * @class:	The ``ledtrig_blkdev`` class (@led_bdev_class)
+ * @attr:	The ``interval`` attribute (@class_attr_interval)
+ * @buf:	The new value (as written to the sysfs attribute)
+ * @count:	The number of bytes written to the attribute
+ *
+ * Sets @led_bdev_interval (after converting to jiffies).
+ *
+ * Context:	Process context.
+ * Return:	@count on success, ``-errno`` on error.
+ */
+static ssize_t interval_store(struct class *const class,
+			      struct class_attribute *const attr,
+			      const char *const buf, const size_t count)
+{
+	unsigned int value;
+	int ret;
+
+	ret = kstrtouint(buf, 0, &value);
+	if (ret != 0)
+		return ret;
+
+	if (value < LED_BDEV_MIN_INT)
+		return -ERANGE;
+
+	WRITE_ONCE(led_bdev_interval, msecs_to_jiffies(value));
+
+	return count;
+}
+
+/* Device and class attributes */
+static DEVICE_ATTR_WO(link_device);
+static DEVICE_ATTR_WO(unlink_device);
+static DEVICE_ATTR_RW(blink_time);
+static DEVICE_ATTR_RW(mode);
+static CLASS_ATTR_RW(interval);
+
+/* Device attributes in LED directory (/sys/class/leds/<led>/...) */
+static struct attribute *led_bdev_attrs[] = {
+	&dev_attr_link_device.attr,
+	&dev_attr_unlink_device.attr,
+	&dev_attr_blink_time.attr,
+	&dev_attr_mode.attr,
+	NULL
+};
+
+/* Unnamed attribute group == no subdirectory */
+static const struct attribute_group led_bdev_attr_group = {
+	.attrs	= led_bdev_attrs,
+};
+
+/* Attribute groups for the trigger */
+static const struct attribute_group *led_bdev_attr_groups[] = {
+	&led_bdev_attr_group,	/* /sys/class/leds/<led>/... */
+	&led_bdev_linked_devs,	/* /sys/class/leds/<led>/linked_devices/ */
+	NULL
+};
+
+/* Trigger registration data */
+static struct led_trigger led_bdev_trigger = {
+	.name		= "blkdev",
+	.activate	= led_bdev_activate,
+	.deactivate	= led_bdev_deactivate,
+	.groups		= led_bdev_attr_groups,
+};
+
+/**
+ * led_bdev_init() - Block device LED trigger initialization.
+ *
+ * Converts default @led_bdev_interval from milliseconds to jiffies, creates
+ * the ``/sys/class/ledtrig_blkdev/interval`` attribute, and registers the LED
+ * trigger.
+ *
+ * Return:	0 on success, ``-errno`` on failure.
+ */
+static int __init led_bdev_init(void)
+{
+	int ret;
+
+	WRITE_ONCE(led_bdev_interval,
+		   msecs_to_jiffies(LED_BDEV_INTERVAL));
+
+	led_bdev_class = class_create(THIS_MODULE, "ledtrig_blkdev");
+	if (IS_ERR(led_bdev_class)) {
+		ret = PTR_ERR(led_bdev_class);
+		goto exit_return;
+	}
+
+	ret = class_create_file(led_bdev_class, &class_attr_interval);
+	if (ret != 0)
+		goto exit_destroy_class;
+
+	ret = led_trigger_register(&led_bdev_trigger);
+
+exit_destroy_class:
+	if (ret != 0)
+		class_destroy(led_bdev_class);	/* removes the class attr */
+exit_return:
+	return ret;
+}
+module_init(led_bdev_init);
+
+/**
+ * led_bdev_exit() - Block device LED trigger module exit.
+ *
+ * Unregisters the LED trigger and removes the
+ * ``/sys/class/ledtrig_blkdev/interval`` attribute.
+ */
+static void __exit led_bdev_exit(void)
+{
+	led_trigger_unregister(&led_bdev_trigger);
+	class_destroy(led_bdev_class);
+}
+module_exit(led_bdev_exit);
+
+MODULE_DESCRIPTION("Block device LED trigger");
+MODULE_AUTHOR("Ian Pilcher <arequipeno@xxxxxxxxx>");
+MODULE_LICENSE("GPL v2");
+MODULE_IMPORT_NS(LEDTRIG_BLKDEV);
-- 
2.31.1