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

[Greg Kroah-Hartman]

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