linux-man.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
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: Wed, 14 Oct 2020 06:40:35 +0200	[thread overview]
Message-ID: <7a4497ad-e595-f328-e0e1-9577dfdbd895@gmail.com> (raw)
In-Reply-To: <8f20d586-9609-ef83-c85a-272e37e684d8@gmail.com>

Hi Tycho,

Ping on the question below!

Thanks,

Michael

On 10/1/20 9:45 AM, Michael Kerrisk (man-pages) wrote:
> 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/

  reply	other threads:[~2020-10-14  8:25 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-30 11:07 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)
2020-10-14  4:40         ` Michael Kerrisk (man-pages) [this message]
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=7a4497ad-e595-f328-e0e1-9577dfdbd895@gmail.com \
    --to=mtk.manpages@gmail.com \
    --cc=ast@kernel.org \
    --cc=bpf@vger.kernel.org \
    --cc=christian@brauner.io \
    --cc=containers@lists.linux-foundation.org \
    --cc=cyphar@cyphar.com \
    --cc=daniel@iogearbox.net \
    --cc=gscrivan@redhat.com \
    --cc=jannh@google.com \
    --cc=keescook@chromium.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-man@vger.kernel.org \
    --cc=luto@amacapital.net \
    --cc=rsesek@google.com \
    --cc=sargun@sargun.me \
    --cc=songliubraving@fb.com \
    --cc=tycho@tycho.pizza \
    --cc=wad@chromium.org \
    --subject='Re: For review: seccomp_user_notif(2) manual page' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).