Messages in this thread | | | From | Linus Torvalds <> | Date | Thu, 24 Aug 2017 12:22:19 -0700 | Subject | Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name |
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On Thu, Aug 24, 2017 at 12:01 PM, Christian Brauner <christian.brauner@canonical.com> wrote: > > I've touched on this in my original message, I wonder whether we currently > support mounting devpts at a different a location and expect an open on a > newly created slave to work.
Yes. That is very much intended to work.
> Say I mount devpts at /mnt and to open("/mnt/ptmx", O_RDWR | O_NOCTTY) and get a new slave pty at /mnt/1 do we > expect open("/mnt/1, O_RDWR | O_NOCTTY) to work?
Yes.
Except you actually don't want to use "/mnt/ptmx". That ptmx node inside the pts filesystem is garbage that we never actually used, because the permissions aren't sane. It should probably be removed, but because somebody *might* have used it, we have left it alone.
So what you're actually *supposed* to do is
- create a ptmx node and a pts directory in /mnt
- mount devpts on /mnt/pts
- use /mnt/ptmx to create new pty's, which should just look up that pts mount directly.
And yes, the pathname should then be /mnt/pts/X for the slave side, and /mnt/ptmx for the master.
In fact, I just tested that TIOCGPTPEER, including using your original test-program (this is me as root in my home directory):
[root@i7 torvalds]# mkdir dummy [root@i7 torvalds]# cd dummy/ [root@i7 dummy]# mknod ptmx c 5 2 [root@i7 dummy]# mkdir pts [root@i7 dummy]# mount -t devpts devpts pts [root@i7 dummy]# ../a.out I point to "/home/torvalds/dummy/pts/0" [root@i7 dummy]# umount pts/ [root@i7 dummy]# cd .. [root@i7 torvalds]# rm -rf dummy
There's two things to note there:
- look at that "I point to" - it's not hardcoded to /dev/pts/X
- look at the pts number: each pts filesystem has its own private numbers, so despite the fact that in another window I *also* have that ptx/0:
[torvalds@i7 linux]$ tty /dev/pts/0
that new devpts instance has its *own* pts/0, which is a completely different pty.
this is one of those big cleanups we did with the pts filesystem some time ago.
Linus
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