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 | 132 ++++++++++++++++++ 4 files changed, 190 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 e34cdeeeb9d4..702601d6a276 100644 --- a/Documentation/ABI/testing/sysfs-block +++ b/Documentation/ABI/testing/sysfs-block @@ -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.) 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..1fd164983f13 --- /dev/null +++ b/Documentation/ABI/testing/sysfs-class-led-trigger-blkdev @@ -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. 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..0b1a9359ec39 --- /dev/null +++ b/Documentation/leds/ledtrig-blkdev.rst @@ -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. -- 2.31.1