Re: [PATCH] ptrace: add ability to retrieve signals without removing them from a queue

[Oleg Nesterov <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On 02/13, Andrey Vagin wrote:
>
> This patch adds a new ptrace request PTRACE_PEEKSIGINFO.
>
> This request is used to retrieve information about a signal with the
> specified sequence number. A siginfo_t structure is copied from the child
> to location data in the parent.
>
> The low 16 bits of addr contains a sequence number of signal in a queue.
> All other bits of addr is used for flags. Currently here is only one
> flag PTRACE_PEEK_SHARED for dumping signals from process-wide shared
> queue. If this flag is not set, a signal is read from a per-thread
> queue.  A result siginfo contains a kernel part of si_code which usually
> striped, but it's required for queuing the same siginfo back during
> restore of pending signals.
>
> If a signal with the specified sequence number doesn't exist, ptrace
> returns ENOENT.
>
> This functionality is required for checkpointing pending signals.

I thinks the patch is correct, and personally I like very much the fact
it is simple. Compared to misc signalfd hacks we discussed before.

Oleg.