From: Oleg Nesterov <oleg@redhat.com>
To: Andrey Wagin <avagin@gmail.com>
Cc: linux-kernel@vger.kernel.org, criu@openvz.org,
linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org,
Alexander Viro <viro@zeniv.linux.org.uk>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
David Howells <dhowells@redhat.com>,
Dave Jones <davej@redhat.com>,
Michael Kerrisk <mtk.manpages@gmail.com>,
Pavel Emelyanov <xemul@parallels.com>,
Cyrill Gorcunov <gorcunov@openvz.org>
Subject: Re: [PATCH 3/3] signalfd: add ability to read siginfo-s without dequeuing signals (v2)
Date: Fri, 8 Feb 2013 20:10:56 +0100 [thread overview]
Message-ID: <20130208191056.GA13674@redhat.com> (raw)
In-Reply-To: <CANaxB-xmSiPfbUAh+rQSgVxBzTXmVQcC7U741WYKaasG3_yc5w@mail.gmail.com>
On 02/08, Andrey Wagin wrote:
>
> 2013/2/7 Oleg Nesterov <oleg@redhat.com>:
> > Andrey, sorry for delay.
> >
> > As for API, I leave this to you and Michael. Not that I like these
> > new flags, but I agree that pread() hack was not pretty too.
> >
> > On 01/29, Andrey Vagin wrote:
> >> +static ssize_t signalfd_peek(struct signalfd_ctx *ctx,
> >> + siginfo_t *info, loff_t *ppos, int queue_mask)
> >> +{
> >> + loff_t seq = *ppos / sizeof(struct signalfd_siginfo);
> >> + int signr = 0;
> >> +
> >> + if (queue_mask & SIGQUEUE_PRIVATE)
> >> + signr = peek_signal(¤t->pending,
> >> + &ctx->sigmask, info, &seq);
> >> + else if (queue_mask & SIGQUEUE_SHARED)
> >> + signr = peek_signal(¤t->signal->shared_pending,
> >> + &ctx->sigmask, info, &seq);
> >> + (*ppos) += sizeof(struct signalfd_siginfo);
> >
> > Now that this can work even with normal read(), we will actually change
> > f_pos. Then perhaps signalfd_fops->llseek() should work too. But this
> > is minor...
>
> lseek works only if FMODE_LSEEK is set.
>
> You have explained why read&lseek have strange semantics for SIGNALFD_PEEK.
>
> >Damn. But after I wrote this email I realized that llseek() probably can't
> > work. Because peek_offset/f_pos/whatever has to be shared with all processes
> > which have this file opened.
Yes. but I thought you decided to ignore this oddity ;)
> So I want to suggest a way how to forbid read() for SIGNALFD_PEEK.
> file->f_pos can be initialized to -1. read() returns EINVAL in this
> case. In a man page we will write that signals can be dumped only with
> help pread(). Is it overload or too ugly?
Well. I do not know. Up to you and Michael.
But honestly, I can't say this all looks really nice. And why do we
need SIGNALFD_PEEK then?
Seriously, perhaps we should simply add signalfd_fops->ioctl() for PEEK.
Or add PTRACE_{PEEK,POKE}_SIGNAL which looks even logical and useful...
And much simpler/straightforward.
But I am not going to argue.
Oleg.
next prev parent reply other threads:[~2013-02-08 19:12 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-22 10:15 [PATCH 0/3] signalfd: a kernel interface for dumping pending signals Andrey Vagin
2013-01-22 10:15 ` [PATCH 1/3] signal: add a helper for dequeuing signals from a specified queue Andrey Vagin
2013-02-05 12:00 ` [PATCH 1/3] signal: add a helper for dequeuing signals from a specified queue (v2) Andrey Vagin
2013-01-22 10:15 ` [PATCH 2/3] signalfd: add ability to choose a private or shared queue Andrey Vagin
2013-02-07 18:17 ` Oleg Nesterov
2013-02-08 0:35 ` Michael Kerrisk (man-pages)
2013-02-08 19:12 ` Oleg Nesterov
2013-01-22 10:15 ` [PATCH 3/3] signalfd: add ability to read siginfo-s without dequeuing signals Andrey Vagin
2013-01-29 19:03 ` [PATCH 3/3] signalfd: add ability to read siginfo-s without dequeuing signals (v2) Andrey Vagin
[not found] ` <CAKgNAkgQA=zK=2ZnytPFU=DH6jr0sja0iy6K+j6c7unheLFniQ@mail.gmail.com>
2013-02-02 7:15 ` Andrey Wagin
2013-02-07 17:34 ` Oleg Nesterov
2013-02-07 21:13 ` Andrey Wagin
2013-02-08 0:51 ` Michael Kerrisk (man-pages)
2013-02-08 19:10 ` Oleg Nesterov [this message]
2013-02-08 20:15 ` Michael Kerrisk (man-pages)
2013-02-09 18:22 ` Oleg Nesterov
2013-02-09 22:53 ` Michael Kerrisk (man-pages)
2013-02-10 10:04 ` [CRIU] " Andrew Vagin
2013-02-11 16:47 ` Oleg Nesterov
2013-02-10 10:07 ` Andrew Vagin
2013-02-11 9:29 ` Denys Vlasenko
2013-02-11 10:59 ` [CRIU] " Andrew Vagin
2013-02-11 14:46 ` Denys Vlasenko
2013-02-11 14:53 ` Pavel Emelyanov
2013-02-11 17:25 ` Denys Vlasenko
2013-02-12 14:50 ` Pavel Emelyanov
2013-01-23 4:19 ` [PATCH 0/3] signalfd: a kernel interface for dumping pending signals Michael Kerrisk (man-pages)
2013-01-23 11:03 ` Andrew Vagin
2013-01-23 12:11 ` Michael Kerrisk (man-pages)
2013-01-23 13:03 ` Andrew Vagin
2013-02-07 18:20 ` Oleg Nesterov
2013-02-08 0:36 ` Michael Kerrisk (man-pages)
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