linux-kernel - Re: [PATCH] prctl: add PR_{SET,GET}_CHILD_REAPER to allow simple process supervision

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Message-Id: <20110816131010.7a6e9a99.akpm@linux-foundation.org>
Date:	Tue, 16 Aug 2011 13:10:10 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Kay Sievers <kay.sievers@...y.org>
Cc:	linux-kernel@...r.kernel.org,
	Lennart Poettering <lennart@...ttering.net>
Subject: Re: [PATCH] prctl: add PR_{SET,GET}_CHILD_REAPER to allow simple
 process supervision

On Fri, 29 Jul 2011 02:01:44 +0200
Kay Sievers <kay.sievers@...y.org> wrote:

> From: Lennart Poettering <lennart@...ttering.net>
> Subject: prctl: add PR_{SET,GET}_CHILD_REAPER to allow simple process supervision
> 
> Userspace service managers/supervisors need to track their started
> services. Many services daemonize by double-forking and get implicitely
> re-parented to PID 1. The process manager will no longer be able to
> receive the SIGCHLD signals for them.
> 
> With this prctl, a service manager can mark itself as a sort of
> 'sub-init' process, able to stay as the parent process for all processes
> created by the started services. All SIGCHLD signals will be delivered
> to the service manager.
> 
> As a side effect, the relevant parent PID information does not get lost
> by a double-fork, which results in a more elaborate process tree and 'ps'
> output.
> 
> This is orthogonal to PID namespaces. PID namespaces are isolated
> from each other, while a service management process usually requires
> the serices to live in the same namespace, to be able to talk to each
> other.
> 
> Users of this will be the systemd per-user instance, which provides
> init-like functionality for the user's login session and D-Bus, which
> activates bus services on on-demand. Both will need init-like capabilities
> to be able to properly keep track of the services they start.
> 

Interesting patch.  I can't immediately see any nasty effects from it..

Did you consider using the existing taskstats capability for this?

The comment block over find_new_reaper() is now incomplete.  Please
update it?

prctl(2) has a manpage.  What's the plan for updating it?

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