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Subject: Re: [PATCH 1/7] signal.h: Define SIGINFO on all architectures
To:     Arseny Maslennikov <ar@cs.msu.ru>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jslaby@suse.com>, Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        linux-kernel@vger.kernel.org
Cc:     "Vladimir D . Seleznev" <vseleznv@altlinux.org>
References: <20190605081906.28938-1-ar@cs.msu.ru>
 <20190605081906.28938-2-ar@cs.msu.ru>
From:   Rob Landley <rob@landley.net>
Message-ID: <43d9e091-7f7c-1175-dca9-06c5e547803d@landley.net>
Date:   Mon, 10 Jun 2019 16:10:39 -0500
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On 6/5/19 3:19 AM, Arseny Maslennikov wrote:
> This complementary patch defines SIGINFO as a synonym for SIGPWR
> on every architecture supported by the kernel.
> The particular signal number chosen does not really matter and is only
> required for the related tty functionality to work properly,
> so if it does not suite expectations, any suggestions are warmly
> welcome.

This was the problem I saw last month: 32 bits worth of signal numbers already
defined, gotta alias something.

> SIGPWR looks like a nice candidate for this role, because it is
> defined on every supported arch; it is currently only used to inform
> PID 1 of power failures, and daemons that care about low-level
> events do not tend to have a controlling terminal.

/dev/console isn't a controlling tty so ctrl-T wouldn't send SIGPWR to PID 1 anyway.

> However, on sparcs SIGPWR is a synonym for SIGLOST, a signal unique
> to that architecture, with a narrow set of intended uses that do not
> combine well with interactively requesting status.
> SIGLOST is not used by any kernel code at the moment.
> I'm not sure there is a more reasonable alternative right now.

The fact it's already _been_ aliased once says it's a good candidate for it. The
easy solution is don't support SIGINFO on sparc until the sparc guys figure out
what to do there and add sparc support in a follow-up patch.

Rob