From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrey Vagin <avagin@openvz.org>
Subject: =?UTF-8?q?=5BPATCH=200/3=5D=20signalfd=3A=20a=20kernel=20interface=20for=20dumping/restoring=20pending=20signals=20=28v2=29?=
Date: Fri, 28 Dec 2012 14:22:58 +0400
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Cc: criu@openvz.org, linux-fsdevel@vger.kernel.org,
	linux-api@vger.kernel.org, Andrey Vagin <avagin@openvz.org>,
	Serge Hallyn <serge.hallyn@canonical.com>,
	Oleg Nesterov <oleg@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Pavel Emelyanov <xemul@parallels.com>,
	Cyrill Gorcunov <gorcunov@openvz.org>,
	Michael Kerrisk <mtk.manpages@gmail.com>
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The idea is simple. We need to get the siginfo for each signal on dump,
and then return it back on restore.

The first problem is that the kernel doesn=E2=80=99t report complete si=
ginfo-s
in user-space. In a signal handler the kernel strips SI_CODE from
siginfo. When a siginfo is received from signalfd, it has a different
format with fixed sizes of fields. The interface of signalfd was
extended. If a signalfd is created with the flag SFD_RAW, it returns
siginfo in a raw format.

rt_sigqueueinfo looks suitable for restoring signals, but it can=E2=80=99=
t send
siginfo with a positive si_code, because these codes are reserved for
the kernel. In the real world each person has right to do anything with
himself, so I think a process should able to send any siginfo to itself=
=2E

v2: add ability to dump signals without dequeuing them.
    pread with non-zero offset is used for this. offset encodes
    a queue (private of shared) and a sequence number of a signal
    in the queue. Thanks to Oleg for this idea.

Cc: Serge Hallyn <serge.hallyn@canonical.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Pavel Emelyanov <xemul@parallels.com>
CC: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>

--=20
1.7.11.7

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