[RFC PATCH v3 00/18] Add block device LED trigger

From: Ian Pilcher
Date: Wed Aug 18 2021 - 22:51:07 EST

Ridiculous or not, here is version 3 of the block device trigger for
"freaking blinkenlights". It addresses basically all of the points
raised in response to the v2 patchset.

* The main body of the code is moved from the block directory into
the LED triggers directory (drivers/leds/trigger/ledtrig-blkdev.c)

The downside of this is that it requires adding an API to the
block subsystem - get_disk_by_name() - which allows the trigger
code to resolve a gendisk when asked to monitor it. I know of
no good way to do this today, and I don't know of a good way to
implement the sysfs API requested by Pavel and Marek without
something like this API.

Other than that, changes to the block subsystem are as minimal as
I can make them - a single pointer added to struct gendisk and
init/cleanup calls when a gendisk is added or deleted.

* This also implements Marek's suggestion of periodically checking
devices for activity, rather than directly blinking LEDs in the
I/O path. This change has the unanticipated benefit of making the
trigger work on pretty much all types of virtual block devices
(device mapper, MD RAID, zRAM, etc.), as well as NVMe SSDs.

* Relationships between devices and LEDs are now many-to-many. An
LED can monitor multiple devices, and multiple LEDs can monitor
any one device. The current "associations" are reflected in two
sysfs directories.

- /sys/class/leds/<led>/block_devices contains links to all devices
associated with an LED, and

- /sys/block/<disk>/blkdev_leds contains links to all LEDs with
which the device is associated.

(The latter directory only exists when the device is associated
with at least one LED.)

* Each LED can be set to show read activity, write activity, or both.
Discards and cache flushes are considered to be writes, as they
affect the state of the device's non-volatile storage.

Ian Pilcher (18):
docs: Add block device (blkdev) LED trigger documentation
block: Add get_disk_by_name() for use by blkdev LED trigger
ledtrig-blkdev: Add file (ledtrig-blkdev.c) for block device LED
ledtrig-blkdev: Add misc. helper functions to blkdev LED trigger
ledtrig-blkdev: Periodically check devices for activity & blink LEDs
block: Add LED trigger pointer to struct gendisk
ledtrig-blkdev: Add function to initialize gendisk ledtrig member
ledtrig-blkdev: Add function to remove LED/device association
ledtrig-blkdev: Add function to disassociate a device from all LEDs
block: Call LED trigger init/cleanup functions
ledtrig-blkdev: Add function to associate a device with an LED
ledtrig-blkdev: Add sysfs attributes to [dis]associate LEDs & devices
ledtrig-blkdev: Add blink_time & interval sysfs attributes
ledtrig-blkdev: Add mode (read/write/rw) sysfs attributue
ledtrig-blkdev: Add function to associate blkdev trigger with LED
ledtrig-blkdev: Add function to disassociate an LED from the trigger
ledtrig-blkdev: Add initialization function
ledtrig-blkdev: Add config option to enable the trigger

Documentation/ABI/testing/sysfs-block | 9 +
.../testing/sysfs-class-led-trigger-blkdev | 48 ++
Documentation/leds/index.rst | 1 +
Documentation/leds/ledtrig-blkdev.rst | 132 +++
block/genhd.c | 28 +
drivers/leds/trigger/Kconfig | 9 +
drivers/leds/trigger/Makefile | 1 +
drivers/leds/trigger/ledtrig-blkdev.c | 770 ++++++++++++++++++
include/linux/genhd.h | 13 +
include/linux/leds.h | 20 +
10 files changed, 1031 insertions(+)
create mode 100644 Documentation/ABI/testing/sysfs-class-led-trigger-blkdev
create mode 100644 Documentation/leds/ledtrig-blkdev.rst
create mode 100644 drivers/leds/trigger/ledtrig-blkdev.c