[PATCH 01/18] docs: Add block device (blkdev) LED trigger documentation

Ian Pilcher
2021-09-03T20:46:00Z

Add Documentation/ABI/testing/sysfs-class-led-trigger-blkdev to
document:

* /sys/class/leds/<led>/blink_time
* /sys/class/leds/<led>/interval
* /sys/class/leds/<led>/mode
* /sys/class/leds/<led>/add_blkdev
* /sys/class/leds/<led>/delete_blkdev
* /sys/class/leds/<led>/block_devices

Add /sys/block/<disk>/blkdev_leds to Documentation/ABI/testing/sysfs-block

Add overview in Documentation/leds/ledtrig-blkdev.rst

Signed-off-by: Ian Pilcher <arequipeno@gmail.com>
---
Documentation/ABI/testing/sysfs-block | 9 ++
.../testing/sysfs-class-led-trigger-blkdev | 48 ++++++
Documentation/leds/index.rst | 1 +
Documentation/leds/ledtrig-blkdev.rst | 144 ++++++++++++++++++
4 files changed, 202 insertions(+)
create mode 100644 Documentation/ABI/testing/sysfs-class-led-trigger-blkdev
create mode 100644 Documentation/leds/ledtrig-blkdev.rst

diff --git a/Documentation/ABI/testing/sysfs-block b/Documentation/ABI/testing/sysfs-block
index a0ed87386639..4d27e2d98091 100644
--- a/Documentation/ABI/testing/sysfs-block
+++ b/Documentation/ABI/testing/sysfs-block
@@ -328,3 +328,12 @@ 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: September 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.)
diff --git a/Documentation/ABI/testing/sysfs-class-led-trigger-blkdev b/Documentation/ABI/testing/sysfs-class-led-trigger-blkdev
new file mode 100644
index 000000000000..514f23f9a72d
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-led-trigger-blkdev
@@ -0,0 +1,48 @@
+What: /sys/class/leds/<led>/blink_time
+Date: September 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: September 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: September 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: September 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: September 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: September 2021
+Contact: Ian Pilcher <arequipeno@gmail.com>
+Description:
+ Directory containing links to all block devices that are
+ associated with this LED.
diff --git a/Documentation/leds/index.rst b/Documentation/leds/index.rst
index e5d63b940045..e3c24e468cbc 100644
--- a/Documentation/leds/index.rst
+++ b/Documentation/leds/index.rst
@@ -10,6 +10,7 @@ LEDs
leds-class
leds-class-flash
leds-class-multicolor
+ ledtrig-blkdev
ledtrig-oneshot
ledtrig-transient
ledtrig-usbport
diff --git a/Documentation/leds/ledtrig-blkdev.rst b/Documentation/leds/ledtrig-blkdev.rst
new file mode 100644
index 000000000000..1a2b6c406258
--- /dev/null
+++ b/Documentation/leds/ledtrig-blkdev.rst
@@ -0,0 +1,144 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=================================
+Block Device (blkdev) LED Trigger
+=================================
+
+Available when ``CONFIG_LEDS_TRIGGER_BLKDEV=y`` or
+``CONFIG_LEDS_TRIGGER_BLKDEV=m``.
+
+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. (See ``Documentation/leds/uleds.rst``.)
+
+Verify that the ``blkdev`` LED trigger is available::
+
+ # grep blkdev /sys/class/leds/<LED>/trigger
+ ... rfkill-none blkdev
+
+(If the previous command produces no output, you may need to load the trigger
+module - ``modprobe ledtrig_blkdev``. If the module is not available, check
+the value of ``CONFIG_LEDS_TRIGGER_BLKDEV`` in your kernel configuration.)
+
+Associate the LED with the ``blkdev`` LED trigger::
+
+ # echo blkdev > /sys/class/leds/<LED>/trigger
+
+ # cat /sys/class/leds/<LED>/trigger
+ ... rfkill-none [blkdev]
+
+Note that several new device attributes are available in the
+``/sys/class/leds/<LED>`` directory.
+
+* ``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. (Note that this is a global setting. Any change affects all
+ LEDs associated with the ``blkdev`` trigger.)
+
+* 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.
--
2.31.1