linux-kernel - Re: [PATCH v3 2/2] tty/sysrq: Add configurable handler to execute a compound action

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Message-ID: <db7fe4ed-19a4-3303-a544-eb789badb8a1@collabora.com>
Date:   Fri, 2 Oct 2020 15:42:52 +0200
From:   Andrzej Pietrasiewicz <andrzej.p@...labora.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, Jiri Slaby <jslaby@...e.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        linux-input@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        kernel@...labora.com
Subject: Re: [PATCH v3 2/2] tty/sysrq: Add configurable handler to execute a
 compound action

Hi,

W dniu 02.10.2020 o 14:54, Greg Kroah-Hartman pisze:
> On Tue, Aug 18, 2020 at 01:28:25PM +0200, Andrzej Pietrasiewicz wrote:
>> Userland might want to execute e.g. 'w' (show blocked tasks), followed
>> by 's' (sync), followed by 1000 ms delay and then followed by 'c' (crash)
>> upon a single magic SysRq. Or one might want to execute the famous "Raising
>> Elephants Is So Utterly Boring" action. This patch adds a configurable
>> handler, triggered with 'C', for this exact purpose. The user specifies the
>> composition of the compound action using syntax similar to getopt, where
>> each letter corresponds to an individual action and a colon followed by a
>> number corresponds to a delay of that many milliseconds, e.g.:
>>
>> ws:1000c
>>
>> or
>>
>> r:100eis:1000ub
> 
> A macro language for sysrq commands, who would have thought...
> 
> Anyway, _why_ would userland want to do something so crazy as this?
> What is the use-case here?
> 

A use-case is Chromebooks which do want to execute 'w', 's',
wait 1000ms and then 'c' under one key combination. Having that supported
upstream brings us one little step closer to those machines running
upstream kernel.

Another argument for such a "macro language" is when a machine's system
keeps degrading over time, possibly degrading (relatively) fast.
"Raising Elephants Is So Utterly Boring" consists of 6 actions, each
of which requires pressing several keys. The user might be unable
to complete all the 6 steps, while a "macro" requires user's involvement
for carrying out just one step.

Regards,

Andrzej