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

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Date:   Fri, 2 Oct 2020 16:02:33 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Andrzej Pietrasiewicz <andrzej.p@...labora.com>
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

On Fri, Oct 02, 2020 at 03:42:52PM +0200, Andrzej Pietrasiewicz wrote:
> 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.

Who is causing that to "execute"?  Some daemon/program?

> 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.

So you want to "preload" some commands ahead of time, for when you get
in trouble?

These should just be debugging / last resort types of things, how
regular are they being used in your systems?

thanks,

greg k-h