linux-kernel - Re: [RFC PATCH v2 00/10] Add configurable block device LED triggers

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Date:   Mon, 9 Aug 2021 20:56:33 +0200
From:   Marek Behún <kabel@...nel.org>
To:     Ian Pilcher <arequipeno@...il.com>, pali@...nel.org
Cc:     linux-block@...r.kernel.org, linux-leds@...r.kernel.org,
        axboe@...nel.dk, pavel@....cz, linux-kernel@...r.kernel.org,
        kernelnewbies@...nelnewbies.org
Subject: Re: [RFC PATCH v2 00/10] Add configurable block device LED triggers

Hello Ian,

thank you for your proposal. Some comments below:

On Sun,  8 Aug 2021 22:32:07 -0500
Ian Pilcher <arequipeno@...il.com> wrote:

> One thing that has not changed is that associations between block
> devices and LEDs are still set via an attribute on the device, rather
> than the LED.  This is much simpler, as the device attribute only has
> to handle a single value (the name of the associated LED), rather than
> potentially handling multiple device names.

It may be simpler, but it is in contrast to how the netdev trigger
works, which already is in upstream for many years. I really think we
should try to have similar sysfs ABIs here. (I understand that the
netdev trigger is currently unable to handle multiple network
interfaces - but it is possible to extend it so.)

> I have modeled the interface for the /sys/block/<DEVICE>/led
> attribute on the sysfs interface used for selecting a trigger.  All
> available LEDs (all LEDs associated with the blkdev trigger) are
> shown when the attribute is read, with the currently selected LED
> enclosed in square brackets ([]).

I think it is reasonable to be able to set something like this:
  led0 : blink on activity on any of [sda, sdb, sdc]
  led1 : blink on activity on sda
  led2 : blink on activity on sdb
  led3 : blink on activity on sdc

If I am reading your code correctly, it looks that only one LED can be
configured for a block device. Is this true? If so, then the above
configuration cannot be set.

Also you are blinking the LED on any request to the block device. I
would rather expect to be able to set the LED to blink on read and on
write. (And possibly on other functions, like discard, or critical
temperature, or error, ...) I would like to know what other people
think about this.

Marek