[CRIU] [PATCH 0/4] signalfd: a kernel interface for dumping/restoring pending signals

[Andrey Vagin]

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’t report complete siginfo-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. We need to choose a queue, so two flags
SFD_GROUP and SFD_PRIVATE were added.

rt_sigqueueinfo looks suitable for restoring signals, but it can’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.

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

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