Messages in this thread | | | From | "Michael Kerrisk (man-pages)" <> | Date | Wed, 23 Jan 2013 05:19:24 +0100 | Subject | Re: [PATCH 0/3] signalfd: a kernel interface for dumping pending signals |
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Hi Andrey,
On Tue, Jan 22, 2013 at 11:15 AM, Andrey Vagin <avagin@openvz.org> wrote: > This patch set adds ability to choose a signal queue and > to read signals without dequeuing them. > > Three new flags are added: > SFD_SHARED_QUEUE -- reads will be from process-wide shared signal queue > SFD_PER_THREAD_QUEUE -- reads will be from per-thread signal queue > SFD_PEEK -- don't dequeue signals
A fuller description of the patch, including information that was in previous versions of this patch would be helpful. Let me see if I can summarize/fill out the API side of things, and ask a few questions along the way (yes, I could answer some of the questions by checking the code, but I want to know what the *intended* behavior is).
The patch series adds a total of 4 flags to signalfd(). In addition to those you list above, the other is
SFD_RAW -- return raw siginfo structs when reading, rather than signalfd_siginfo
The intention is that these flags be used in conjunction with pread(), to peek at queued signals. The 'offset' argument is treated as a position. Thus, for example, to non-destructively read all of the per-thread signals in raw form from the per-thread queue, one would write
fd = signalfd(-1, SFD_PER_THREAD_QUEUE | SFD_RAW | SFD_PEEK) for (j = 0; ; j++) { s = pread(fd, buf, ocunt, j) if (s == 0) /* No more signals */ break; }
Right?
Now some questions. I don't require all of the following, but I'm wanting to know what's possible, for documentation purposes.
Q1: with this patch series, is it permissible to specify SFD_PER_THREAD_QUEUE or SFD_SHARED_QUEUE without specifying either SFD_PEEK or SFD_QUEUE? In other words, can one do traditional signalfd_siginfo reads, but selecting from a specific queue.
Q2: Is it possible to specify SFD_PEEK without SFD_RAW, so that one can peek at siginfo structs rather than signalfd_siginfo structs?
Q3: Is it possible to specify SFD_RAW without SFD_PEEK, so that one can destructively read signalfd_siginfo structs? Can that be done using any read interface (read(), pread(), etc.)?
Q4: Is it possible to specify both SFD_PER_THREAD_QUEUE and SFD_SHARED_QUEUE? In that case, in what order are signals read from the two queues?
Thanks,
Michael
> 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> > > -- > 1.7.11.7 >
-- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Author of "The Linux Programming Interface"; http://man7.org/tlpi/
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