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Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup

From "H. Peter Anvin" <hpa@zytor.com>
Newsgroups linux.kernel
Subject Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup
Date 2016-04-09 16:20 +0200
Message-ID <rm1TY-6j8-3@gated-at.bofh.it> (permalink)
References <rkmSS-2Qr-13@gated-at.bofh.it> <rkohY-3Gi-3@gated-at.bofh.it> <rlkFl-6uI-37@gated-at.bofh.it> <rlJX4-7e-27@gated-at.bofh.it> <rm0XT-5Cn-13@gated-at.bofh.it>
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On April 9, 2016 6:09:09 AM PDT, One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk> wrote:
>
>> If anyone has a better idea on how userspace should connect the
>master
>> pty file descriptor the slave file descriptor, I would be willing to
>> implement that instead.
>
>If we are willing to go away from the existing mess of a tty interface
>inflicted on us by BSD and then mashed up by POSIX then a syscall of
>
>  int err = ptypair(int fd[2], int perms, int flags);
>
>[where flags is the O_ ones we usually need to cover (CLOEXEC etc) and
>maybe even some kind of "private" flag to say don't even expose it via
>devpts).
>
>would do remarkably sane things to the majoirty of use cases as it
>breaks
>the dependence on grantpt and also the historic screwup that pty pairs
>aren't allocated atomically with both file handles returned as pipe()
>does.
>
>Alan

We don't even need to do that if we'd be willing to change the user space interface... if we could rely on the POSIX interface then posix_openpt() could simply open /dev/pts/ptmx and everything would just work.

The trick here is how to make it work in the presence of some extremely bad practices in existing userspace.
-- 
Sent from my Android device with K-9 Mail. Please excuse brevity and formatting.

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[PATCH 00/13] devpts: New instances for every mount ebiederm@xmission.com (Eric W. Biederman) - 2016-04-05 02:20 +0200
  [PATCH 04/13] devpts: Stop rolling devpts_remount by hand in devpts_mount "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-05 03:50 +0200
  [PATCH 05/13] devpts: Fail early (if appropriate) on overmount "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-05 03:50 +0200
  [PATCH 08/13] devpts: Make devpts_kill_sb safe if fsi is NULL "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-05 03:50 +0200
  [PATCH 03/13] devpts: Cleanup newinstance parsing "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-05 03:50 +0200
  [PATCH 06/13] devpts: Use the same default mode for both /dev/ptmx and dev/pts/ptmx "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-05 03:50 +0200
  [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-05 03:50 +0200
    [PATCH 09/13] devpts: Move the creation of /dev/pts/ptmx into fill_super "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-05 03:50 +0200
    [PATCH 02/13] devpts: More obvious check for the system devpts in pty allocation "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-05 03:50 +0200
    [PATCH 13/13] devpts: Kill the DEVPTS_MULTIPLE_INSTANCE config option "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-05 03:50 +0200
    [PATCH 07/13] devpts: Move parse_mount_options into fill_super "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-05 03:50 +0200
    [PATCH 12/13] devpts: Always return a distinct instance when mounting "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-05 04:00 +0200
    [PATCH 11/13] vfs: Implement mount_super_once "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-05 04:00 +0200
    [PATCH 10/13] devpts: Simplify devpts_mount by using mount_nodev "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-05 04:00 +0200
    Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated  devpts via path lookup Al Viro <viro@ZenIV.linux.org.uk> - 2016-04-05 05:00 +0200
      Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated  devpts via path lookup Al Viro <viro@ZenIV.linux.org.uk> - 2016-04-05 05:10 +0200
        Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup ebiederm@xmission.com (Eric W. Biederman) - 2016-04-08 21:10 +0200
    Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated  devpts via path lookup Linus Torvalds <torvalds@linux-foundation.org> - 2016-04-07 18:10 +0200
      Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup ebiederm@xmission.com (Eric W. Biederman) - 2016-04-08 21:10 +0200
        Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated  devpts via path lookup Linus Torvalds <torvalds@linux-foundation.org> - 2016-04-08 21:10 +0200
          Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup ebiederm@xmission.com (Eric W. Biederman) - 2016-04-08 22:20 +0200
          Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated  devpts via path lookup Andy Lutomirski <luto@amacapital.net> - 2016-04-08 22:50 +0200
            Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup ebiederm@xmission.com (Eric W. Biederman) - 2016-04-08 23:50 +0200
              Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated  devpts via path lookup Andy Lutomirski <luto@amacapital.net> - 2016-04-09 00:00 +0200
              Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated  devpts via path lookup Linus Torvalds <torvalds@linux-foundation.org> - 2016-04-09 00:00 +0200
                Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup ebiederm@xmission.com (Eric W. Biederman) - 2016-04-09 01:20 +0200
        Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated  devpts via path lookup One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk> - 2016-04-09 15:20 +0200
          Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup "H. Peter Anvin" <hpa@zytor.com> - 2016-04-09 16:20 +0200
            Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup ebiederm@xmission.com (Eric W. Biederman) - 2016-04-09 17:00 +0200
              Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup "H. Peter Anvin" <hpa@zytor.com> - 2016-04-10 00:50 +0200
                Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated  devpts via path lookup Linus Torvalds <torvalds@linux-foundation.org> - 2016-04-10 02:10 +0200
                Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup "H. Peter Anvin" <hpa@zytor.com> - 2016-04-10 02:20 +0200
                Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated  devpts via path lookup Linus Torvalds <torvalds@linux-foundation.org> - 2016-04-10 02:20 +0200
                Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated  devpts via path lookup Andy Lutomirski <luto@amacapital.net> - 2016-04-10 02:50 +0200
                Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup "H. Peter Anvin" <hpa@zytor.com> - 2016-04-11 17:10 +0200
                Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated  devpts via path lookup Al Viro <viro@ZenIV.linux.org.uk> - 2016-04-12 03:40 +0200
                Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated  devpts via path lookup Andy Lutomirski <luto@amacapital.net> - 2016-04-11 22:20 +0200
                Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup "H. Peter Anvin" <hpa@zytor.com> - 2016-04-11 22:30 +0200
                Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup ebiederm@xmission.com (Eric W. Biederman) - 2016-04-12 01:50 +0200
                Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated  devpts via path lookup Linus Torvalds <torvalds@linux-foundation.org> - 2016-04-12 02:10 +0200
                Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup ebiederm@xmission.com (Eric W. Biederman) - 2016-04-12 02:30 +0200
                Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated  devpts via path lookup Linus Torvalds <torvalds@linux-foundation.org> - 2016-04-12 03:20 +0200
                Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup "H. Peter Anvin" <hpa@zytor.com> - 2016-04-12 03:20 +0200
                Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup ebiederm@xmission.com (Eric W. Biederman) - 2016-04-12 03:40 +0200
                Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated  devpts via path lookup Al Viro <viro@ZenIV.linux.org.uk> - 2016-04-12 03:50 +0200
                Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated  devpts via path lookup Al Viro <viro@ZenIV.linux.org.uk> - 2016-04-12 03:40 +0200
                Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup ebiederm@xmission.com (Eric W. Biederman) - 2016-04-12 04:30 +0200
                Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup ebiederm@xmission.com (Eric W. Biederman) - 2016-04-11 22:30 +0200
                Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated  devpts via path lookup Andy Lutomirski <luto@amacapital.net> - 2016-04-12 19:50 +0200
                Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated  devpts via path lookup Linus Torvalds <torvalds@linux-foundation.org> - 2016-04-12 20:20 +0200
                Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated  devpts via path lookup "H. Peter Anvin" <hpa@zytor.com> - 2016-04-12 21:20 +0200
                [PATCH 01/16] devpts: Attempting to get it right ebiederm@xmission.com (Eric W. Biederman) - 2016-04-15 17:50 +0200
                [PATCH 08/16] devpts: Stop rolling devpts_remount by hand in devpts_mount "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-15 17:50 +0200
                [PATCH 05/16] vfs: Allow unlink, and rename on expirable file mounts "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-15 17:50 +0200
                [PATCH 04/16] devpts: Teach /dev/ptmx to automount the appropriate devpts via path lookup "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-15 17:50 +0200
                [PATCH 09/16] devpts: Fail early (if appropriate) on overmount "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-15 17:50 +0200
                [PATCH 10/16] devpts: Move parse_mount_options into fill_super "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-15 17:50 +0200
                [PATCH 06/16] devpts: More obvious check for the system devpts in pty allocation "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-15 17:50 +0200
                [PATCH 01/16] devpts: Use the same default mode for both /dev/ptmx and dev/pts/ptmx "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-15 17:50 +0200
                [PATCH 12/16] devpts: Move the creation of /dev/pts/ptmx into fill_super "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-15 18:00 +0200
                [PATCH 11/16] devpts: Make devpts_kill_sb safe if fsi is NULL "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-15 18:00 +0200
                [PATCH 16/16] devpts: Kill the DEVPTS_MULTIPLE_INSTANCE config option "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-15 18:00 +0200
                [PATCH 15/16] devpts: Always return a distinct instance when mounting "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-15 18:00 +0200
                [PATCH 13/16] devpts: Simplify devpts_mount by using mount_nodev "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-15 18:00 +0200
                [PATCH 14/16] vfs: Implement mount_super_once "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-15 18:00 +0200
                Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup ebiederm@xmission.com (Eric W. Biederman) - 2016-04-12 02:10 +0200
                Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated  devpts via path lookup Linus Torvalds <torvalds@linux-foundation.org> - 2016-04-12 02:10 +0200
                Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup ebiederm@xmission.com (Eric W. Biederman) - 2016-04-12 02:40 +0200
                Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated  devpts via path lookup Linus Torvalds <torvalds@linux-foundation.org> - 2016-04-12 03:00 +0200
                Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup ebiederm@xmission.com (Eric W. Biederman) - 2016-04-11 22:20 +0200

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