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

From ebiederm@xmission.com (Eric W. Biederman)
Newsgroups linux.kernel
Subject Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup
Date 2016-04-12 03:40 +0200
Message-ID <rmVt8-7gi-5@gated-at.bofh.it> (permalink)
References (13 earlier) <rmQts-3h1-3@gated-at.bofh.it> <rmQD7-3mh-1@gated-at.bofh.it> <rmTKG-5Lf-11@gated-at.bofh.it> <rmU42-6dm-7@gated-at.bofh.it> <rmV9M-76T-13@gated-at.bofh.it>
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"H. Peter Anvin" <hpa@zytor.com> writes:

> On April 11, 2016 5:10:47 PM PDT, ebiederm@xmission.com wrote:
>>Linus Torvalds <torvalds@linux-foundation.org> writes:
>>
>>> On Mon, Apr 11, 2016 at 4:37 PM, Eric W. Biederman
>>> <ebiederm@xmission.com> wrote:
>>>>
>>>> My practical concern if we worked through the implementation details
>>>> would be how would it interact with people who bind mount
>>/dev/pts/ptmx
>>>> on top of /dev/ptmx.  We might get some strange new errors.
>>>
>>> Yes, please don't let's play "clever" games. The semantics should be
>>> fairly straightforward.
>>
>>Actually for me this is about keeping the semantics simpler, and coming
>>up with a higher performance implementation.
>>
>>A dentry that does an automount is already well defined.
>>
>>Making the rule that accessing /dev/ptmx causes an automount of
>>/dev/pts/ptmx on top of the device node at /dev/ptmx is really simple,
>>with no special games.  It also makes it more obvious to userspace what
>>is going on.  AKA allows userspace to know which superblock does an
>>open
>>ptmx master tty belongs to (and it happens in a backwards and forwards
>>compatible way).
>>
>>My only concern is with this very minor change in semantics will
>>anything care.  I need to implement and test to find out.
>>
>>I think I see an implementation that Al won't grumble too loudly about.
>>
>>Anyway I am going to try this and see what I can see.
>>
>>Eric
>
> Why bother with an automount?  You can look up ../ptmx from the devpts
> get_super method and just do the bind mount once.  No fuss, no muss.
> What's wrong with that?

Perhaps I am reading the code wrong but as I read it that information is
simply not available in get_super.

Eric

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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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