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Thu, 09 Sep 2021 15:25:23 -0700 (PDT) From: Ian Pilcher To: axboe@kernel.dk, pavel@ucw.cz Cc: linux-leds@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, gregkh@linuxfoundation.org, kabel@kernel.org Subject: [PATCH v2 01/15] docs: Add block device (blkdev) LED trigger documentation Date: Thu, 9 Sep 2021 17:24:59 -0500 Message-Id: <20210909222513.2184795-2-arequipeno@gmail.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210909222513.2184795-1-arequipeno@gmail.com> References: <20210909222513.2184795-1-arequipeno@gmail.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-leds@vger.kernel.org Add Documentation/ABI/testing/sysfs-class-led-trigger-blkdev to document: * /sys/class/leds//blink_time * /sys/class/leds//interval * /sys/class/leds//mode * /sys/class/leds//link_device * /sys/class/leds//unlink_device * /sys/class/leds//linked_devices Add /sys/block//linked_leds to Documentation/ABI/testing/sysfs-block Add overview in Documentation/leds/ledtrig-blkdev.rst Signed-off-by: Ian Pilcher --- Documentation/ABI/testing/sysfs-block | 9 ++ .../testing/sysfs-class-led-trigger-blkdev | 46 ++++++ Documentation/leds/index.rst | 1 + Documentation/leds/ledtrig-blkdev.rst | 138 ++++++++++++++++++ 4 files changed, 194 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//linked_leds +Date: September 2021 +Contact: Ian Pilcher +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..9f75d0bccceb --- /dev/null +++ b/Documentation/ABI/testing/sysfs-class-led-trigger-blkdev @@ -0,0 +1,46 @@ +What: /sys/class/leds//blink_time +Date: September 2021 +Contact: Ian Pilcher +Description: + Time (in milliseconds) that the LED will be on during a single + "blink". + +What: /sys/class/leds//interval +Date: September 2021 +Contact: Ian Pilcher +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//mode +Date: September 2021 +Contact: Ian Pilcher +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//link_device +Date: September 2021 +Contact: Ian Pilcher +Description: + Associate a block device with this LED by writing its kernel + name (as shown in /sys/block) to this attribute. + +What: /sys/class/leds//unlink_device +Date: September 2021 +Contact: Ian Pilcher +Description: + Remove the association between this LED and a block device by + writing the device's kernel name to this attribute. + +What: /sys/class/leds//linked_devices +Date: September 2021 +Contact: Ian Pilcher +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..a4acc532f31b --- /dev/null +++ b/Documentation/leds/ledtrig-blkdev.rst @@ -0,0 +1,138 @@ +.. 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//linked_leds``) + +Overview +======== + +.. note:: + The examples below use ```` 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//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//trigger + + # cat /sys/class/leds//trigger + ... rfkill-none [blkdev] + +Note that several new device attributes are available in the +``/sys/class/leds/`` 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. + +* ``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 ``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//link_device + + # ls /sys/class/leds//linked_devices + sda + +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//blink_time``. (But see **interval and blink_time** +below.) + +Associate a second device with the LED:: + + # echo sdb > /sys/class/leds//link_device + + # ls /sys/class/leds//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/block/sd{a,b}/linked_leds + /sys/block/sda/linked_leds: + + + /sys/block/sdb/linked_leds: + + +(The ``linked_leds`` directory only exists when the block device is linked to +at least one LED.) + +``interval`` and ``blink_time`` +=============================== + +* The ``interval`` attribute is a global setting. Changing the value via + ``/sys/class/leds//interval`` will change it for all LEDs associated with + the ``blkdev`` 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 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 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.