From: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
To: Tycho Andersen <tycho@tycho.pizza>
Cc: mtk.manpages@gmail.com, Sargun Dhillon <sargun@sargun.me>,
Kees Cook <keescook@chromium.org>,
Christian Brauner <christian@brauner.io>,
linux-man <linux-man@vger.kernel.org>,
lkml <linux-kernel@vger.kernel.org>,
Aleksa Sarai <cyphar@cyphar.com>, Jann Horn <jannh@google.com>,
Alexei Starovoitov <ast@kernel.org>,
wad@chromium.org, bpf@vger.kernel.org,
Song Liu <songliubraving@fb.com>,
Daniel Borkmann <daniel@iogearbox.net>,
Andy Lutomirski <luto@amacapital.net>,
Linux Containers <containers@lists.linux-foundation.org>,
Giuseppe Scrivano <gscrivan@redhat.com>,
Robert Sesek <rsesek@google.com>
Subject: Re: For review: seccomp_user_notif(2) manual page
Date: Thu, 1 Oct 2020 09:45:19 +0200 [thread overview]
Message-ID: <8f20d586-9609-ef83-c85a-272e37e684d8@gmail.com> (raw)
In-Reply-To: <20200930230327.GA1260245@cisco>
On 10/1/20 1:03 AM, Tycho Andersen wrote:
> On Wed, Sep 30, 2020 at 10:34:51PM +0200, Michael Kerrisk (man-pages) wrote:
>> Hi Tycho,
>>
>> Thanks for taking time to look at the page!
>>
>> On 9/30/20 5:03 PM, Tycho Andersen wrote:
>>> On Wed, Sep 30, 2020 at 01:07:38PM +0200, Michael Kerrisk (man-pages) wrote:
[...]
>>>> ┌─────────────────────────────────────────────────────┐
>>>> │FIXME │
>>>> ├─────────────────────────────────────────────────────┤
>>>> │Interestingly, after the event had been received, │
>>>> │the file descriptor indicates as writable (verified │
>>>> │from the source code and by experiment). How is this │
>>>> │useful? │
>>>
>>> You're saying it should just do EPOLLOUT and not EPOLLWRNORM? Seems
>>> reasonable.
>>
>> No, I'm saying something more fundamental: why is the FD indicating as
>> writable? Can you write something to it? If yes, what? If not, then
>> why do these APIs want to say that the FD is writable?
>
> You can't via read(2) or write(2), but conceptually NOTIFY_RECV and
> NOTIFY_SEND are reading and writing events from the fd. I don't know
> that much about the poll interface though -- is it possible to
> indicate "here's a pseudo-read event"? It didn't look like it, so I
> just (ab-)used POLLIN and POLLOUT, but probably that's wrong.
I think the POLLIN thing is fine.
So, I think maybe I now understand what you intended with setting
POLLOUT: the notification has been received ("read") and now the
FD can be used to NOTIFY_SEND ("write") a response. Right?
If that's correct, I don't have a problem with it. I just wonder:
is it useful? IOW: are there situations where the process doing the
NOTIFY_SEND might want to test for POLLOUT because the it doesn't
know whether a NOTIFY_RECV has occurred?
Thanks,
Michael
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
next prev parent reply other threads:[~2020-10-01 7:45 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-30 11:07 For review: seccomp_user_notif(2) manual page Michael Kerrisk (man-pages)
2020-09-30 15:03 ` Tycho Andersen
2020-09-30 15:11 ` Tycho Andersen
2020-09-30 20:34 ` Michael Kerrisk (man-pages)
2020-09-30 23:03 ` Tycho Andersen
2020-09-30 23:11 ` Jann Horn
2020-09-30 23:24 ` Tycho Andersen
2020-10-01 1:52 ` Jann Horn
2020-10-01 2:14 ` Jann Horn
2020-10-25 16:31 ` Michael Kerrisk (man-pages)
2020-10-26 15:54 ` Jann Horn
2020-10-27 6:14 ` Michael Kerrisk (man-pages)
2020-10-27 10:28 ` Jann Horn
2020-10-28 6:31 ` Sargun Dhillon
2020-10-28 9:43 ` Jann Horn
2020-10-28 17:43 ` Sargun Dhillon
2020-10-28 18:20 ` Jann Horn
2020-10-01 7:49 ` Michael Kerrisk (man-pages)
2020-10-26 0:32 ` Kees Cook
2020-10-26 9:51 ` Jann Horn
2020-10-26 10:31 ` Jann Horn
2020-10-28 22:56 ` Kees Cook
2020-10-29 1:11 ` Jann Horn
[not found] ` <20201029021348.GB25673@cisco>
2020-10-29 4:26 ` Jann Horn
2020-10-28 22:53 ` Kees Cook
2020-10-29 1:25 ` Jann Horn
2020-10-01 7:45 ` Michael Kerrisk (man-pages) [this message]
2020-10-14 4:40 ` Michael Kerrisk (man-pages)
2020-09-30 15:53 ` Jann Horn
2020-10-01 12:54 ` Christian Brauner
2020-10-01 15:47 ` Jann Horn
2020-10-01 16:58 ` Tycho Andersen
2020-10-01 17:12 ` Christian Brauner
2020-10-14 5:41 ` Michael Kerrisk (man-pages)
2020-10-01 18:18 ` Jann Horn
2020-10-01 18:56 ` Tycho Andersen
2020-10-01 17:05 ` Christian Brauner
2020-10-15 11:24 ` Michael Kerrisk (man-pages)
2020-10-15 20:32 ` Jann Horn
2020-10-16 18:29 ` Michael Kerrisk (man-pages)
2020-10-17 0:25 ` Jann Horn
2020-10-24 12:52 ` Michael Kerrisk (man-pages)
2020-10-26 9:32 ` Jann Horn
2020-10-26 9:47 ` Michael Kerrisk (man-pages)
2020-09-30 23:39 ` Kees Cook
2020-10-15 11:24 ` Michael Kerrisk (man-pages)
2020-10-26 0:19 ` Kees Cook
2020-10-26 9:39 ` Michael Kerrisk (man-pages)
2020-10-01 12:36 ` Christian Brauner
2020-10-15 11:23 ` Michael Kerrisk (man-pages)
2020-10-01 21:06 ` Sargun Dhillon
2020-10-01 23:19 ` Tycho Andersen
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