Add Documentation/ABI/testing/sysfs-class-led-trigger-blkdev to
document:
* /sys/class/leds/<led>/blink_time
* /sys/class/leds/<led>/mode
* /sys/class/leds/<led>/link_device
* /sys/class/leds/<led>/unlink_device
* /sys/class/leds/<led>/linked_devices
* /sys/class/ledtrig_blkdev/interval
Add /sys/block/<disk>/linked_leds to
Documentation/ABI/testing/sysfs-block.
Add overview in Documentation/leds/ledtrig-blkdev.rst.
Signed-off-by: Ian Pilcher <arequipeno@xxxxxxxxx>
---
Documentation/ABI/testing/sysfs-block | 9 ++
.../testing/sysfs-class-led-trigger-blkdev | 50 ++++++
Documentation/leds/index.rst | 1 +
Documentation/leds/ledtrig-blkdev.rst | 149 ++++++++++++++++++
4 files changed, 209 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..80d4becc4e6d 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>/linked_leds
+Date: September 2021
+Contact: Ian Pilcher <arequipeno@xxxxxxxxx>
+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..b8730d450dbf
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-led-trigger-blkdev
@@ -0,0 +1,50 @@
+What: /sys/class/leds/<led>/blink_time
+Date: September 2021
+Contact: Ian Pilcher <arequipeno@xxxxxxxxx>
+Description:
+ Time (in milliseconds) that the LED will be on during a single
+ "blink".
+
+What: /sys/class/leds/<led>/mode
+Date: September 2021
+Contact: Ian Pilcher <arequipeno@xxxxxxxxx>
+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>/link_device
+Date: September 2021
+Contact: Ian Pilcher <arequipeno@xxxxxxxxx>
+Description:
+ Associate a block device with this LED by writing the path to
+ the device special file (e.g. /dev/sda) to this attribute.
+ Symbolic links are followed. Optionally, the leading "/dev/"
+ may be omitted.
+
+What: /sys/class/leds/<led>/unlink_device
+Date: September 2021
+Contact: Ian Pilcher <arequipeno@xxxxxxxxx>
+Description:
+ Remove the association between this LED and a block device by
+ writing the path to the device special file (e.g. /dev/sda) to
+ this attribute. Symbolic links are followed. Optionally, the
+ leading "/dev/" may be omitted.
+
+What: /sys/class/leds/<led>/linked_devices
+Date: September 2021
+Contact: Ian Pilcher <arequipeno@xxxxxxxxx>
+Description:
+ Directory containing links to all block devices that are
+ associated with this LED. (Note that the names of the
+ symbolic links in this directory are *kernel* names, which
+ may not match the device special file paths written to
+ link_device and unlink_device.)
+
+What: /sys/class/ledtrig_blkdev/interval
+Date: September 2021
+Contact: Ian Pilcher <arequipeno@xxxxxxxxx>
+Description:
+ Frequency (in milliseconds) with which block devices associated
+ with the blkdev LED trigger will be checked for activity.
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..af319125ab25
--- /dev/null
+++ b/Documentation/leds/ledtrig-blkdev.rst
@@ -0,0 +1,149 @@
+.. 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>/linked_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.
+
+* ``link_device`` and ``unlink_device`` are used to manage the set of block
+ devices associated with this LED. The LED will blink in response to read or
+ write activity on its linked devices.
+
+* ``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.
+ (The minimum value is 10 milliseconds.)
+
+* The ``linked_devices`` directory will contain a symbolic link to every device
+ that is associated with this LED.
+
+Link a block device to the LED::
+
+ # echo sda > /sys/class/leds/<LED>/link_device
+
+ # ls /sys/class/leds/<LED>/linked_devices
+ sda
+
+(The value written to ``link_device`` must be the path of the device special
+file, such as ``/dev/sda``, that represents the block device - or the path of a
+symbolic link to such a device special file. The example above works because it
+is possible to omit the leading ``/dev``.)
+
+Read 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_time``. (But see **interval and blink_time**
+below.)
+
+Associate a second device with the LED::
+
+ # echo sdb > /sys/class/leds/<LED>/link_device
+
+ # ls /sys/class/leds/<LED>/linked_devices
+ sda sdb
+
+When a block device is linked to one or more LEDs, the LEDs are linked from
+the device's ``linked_leds`` directory::
+
+ # ls /sys/class/block/sd{a,b}/linked_leds
+ /sys/class/block/sda/linked_leds:
+ <LED>
+
+ /sys/class/block/sdb/linked_leds:
+ <LED>
+
+(The ``linked_leds`` directory only exists when the block device is linked to
+at least one LED.)
+
+``interval`` and ``blink_time``
+===============================
+
+* By default, linked block devices are checked for activity every 100
+ milliseconds. This frequency can be changed via the
+ ``/sys/class/ledtrig_blkdev/interval`` attribute. (The minimum value is 25
+ milliseconds.)
+
+* 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. Thus
+ (assuming that activity of the relevant type has occurred on one of an LED's
+ linked 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 already in
+ in the process of blinking, so setting a ``blink_time`` greater than or equal
+ to ``interval`` will cause some blinks to be missed.
+
+* 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
+ "always 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
+ * partitions on block devics that support them
+
+* The names of the symbolic links in ``/sys/class/leds/<LED>/linked_devices``
+ are **kernel** names, which may not match the paths used for
+ ``link_device`` and ``unlink_device``. This is most likely when a symbolic
+ link is used to refer to the device (as is common with logical volumes), but
+ it can be true for any device, because nothing prevents the creation of
+ device special files with arbitrary names (``sudo mknod /foo b 8 0``).
+
+* 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
