Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1713217

Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name

From Linus Torvalds <torvalds@linux-foundation.org>
Newsgroups linux.kernel
Subject Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name
Date 2017-08-16 20:30 +0200
Message-ID <ufbeO-25d-31@gated-at.bofh.it> (permalink)
References <ufa94-1so-11@gated-at.bofh.it>
Organization linux.* mail to news gateway

Show all headers | View raw

On Wed, Aug 16, 2017 at 10:12 AM, Christian Brauner
<christian.brauner@ubuntu.com> wrote:
>
> Recently the kernel has implemented the TIOCGPTPEER ioctl() call which allows
> users to retrieve an fd for the slave side of a pty solely based on the
> corresponding fd for the master side. The ioctl()-based fd retrieval however
> causes the "/proc/<pid>/fd/<pty-slave-fd>" symlink to point to the wrong dentry.
> Currently, it will always point to "/". The following simple program can be used
> to illustrate the problem when run on a system that implements the TIOCGPTPEER
> ioctl() call.

I think your patch is wrong - we need to actually use the *right*
path, rather than hardcode "/dev/pts/%d" in there.

Hardcoding "/dev/pts/%d" is something that user space can already do.
The kernel can and should do better.

That "dynamic_dname()" helper is for things that don't really have a
real pathname at all, so things like pipes and other file descriptors
that were opened without an associated entry in a filesystem (sockets,
other "special" inodes with no filesystem backing).

For things like pts slaves, we actually *do* have a real pathname -
and we should expose it. If the devpts filesystem is mounted somewhere
else than /dev/pts, it should give that correct pathname.

I also think your test program is a bit buggy, and silly:

>         ret = snprintf(path, 4096, "/proc/self/fd/%d", slave);
>         if (ret < 0 || ret >= 4096)
>                 goto on_error;
>
>         ret = readlink(path, buf, sizeof(buf));
>         if (ret < 0)
>                 goto on_error;
>         printf("I point to \"%s\"\n", buf);

This just smells wrong to me. And not just because you don't
NUL-terminate the readlink() return value (or just use "%.*s" with
ret, buf) .

We should just give people a better way to get the pathname than that
readlink on /proc/self/fd/<fd> thing. It's kind of ridiculous that we
don't. We already have a "getcwd()" system call that only does it for
cwd.

So I think we could/should just add a system call for 'fdname()' or similar.

                Linus

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH 0/1] devpts: use dynamic_dname() to generate proc name Christian Brauner <christian.brauner@ubuntu.com> - 2017-08-16 19:20 +0200
  Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-16 20:30 +0200
    Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-16 20:50 +0200
      Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Christian Brauner <christian.brauner@canonical.com> - 2017-08-16 21:50 +0200
        Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-16 22:00 +0200
          Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-16 22:20 +0200
            Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-16 22:40 +0200
              Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-16 23:10 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Christian Brauner <christian.brauner@canonical.com> - 2017-08-16 23:40 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-16 23:50 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-17 00:00 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Christian Brauner <christian.brauner@canonical.com> - 2017-08-17 00:10 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Christian Brauner <christian.brauner@canonical.com> - 2017-08-17 00:30 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name ebiederm@xmission.com (Eric W. Biederman) - 2017-08-23 17:40 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Christian Brauner <christian.brauner@canonical.com> - 2017-08-23 23:20 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name ebiederm@xmission.com (Eric W. Biederman) - 2017-08-17 00:50 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-17 01:00 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name ebiederm@xmission.com (Eric W. Biederman) - 2017-08-17 02:00 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-17 02:10 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name ebiederm@xmission.com (Eric W. Biederman) - 2017-08-17 03:30 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Stefan Lippers-Hollmann <s.l-h@gmx.de> - 2017-08-24 02:30 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-24 02:50 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-24 03:20 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name ebiederm@xmission.com (Eric W. Biederman) - 2017-08-24 03:30 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-24 03:40 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-24 03:50 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-24 04:10 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name ebiederm@xmission.com (Eric W. Biederman) - 2017-08-24 05:20 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-24 05:30 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name ebiederm@xmission.com (Eric W. Biederman) - 2017-08-24 18:00 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Stefan Lippers-Hollmann <s.l-h@gmx.de> - 2017-08-24 06:30 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name ebiederm@xmission.com (Eric W. Biederman) - 2017-08-24 18:00 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-24 20:00 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-24 20:10 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-24 20:20 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-24 20:40 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-24 20:40 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Stefan Lippers-Hollmann <s.l-h@gmx.de> - 2017-08-24 22:30 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-24 22:30 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name ebiederm@xmission.com (Eric W. Biederman) - 2017-08-24 20:50 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-24 21:00 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name ebiederm@xmission.com (Eric W. Biederman) - 2017-08-24 21:30 +0200
                [PATCH v3] pty: Repair TIOCGPTPEER ebiederm@xmission.com (Eric W. Biederman) - 2017-08-24 22:20 +0200
                Re: [PATCH v3] pty: Repair TIOCGPTPEER Stefan Lippers-Hollmann <s.l-h@gmx.de> - 2017-08-24 23:10 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-24 21:30 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-24 21:30 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name ebiederm@xmission.com (Eric W. Biederman) - 2017-08-24 22:50 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-24 23:10 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name ebiederm@xmission.com (Eric W. Biederman) - 2017-08-25 01:10 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-25 01:30 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name Christian Brauner <christian.brauner@canonical.com> - 2017-08-25 01:40 +0200
                Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name ebiederm@xmission.com (Eric W. Biederman) - 2017-08-24 21:50 +0200
            Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name ebiederm@xmission.com (Eric W. Biederman) - 2017-08-17 03:40 +0200

csiph-web