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

Christian Brauner
2017-08-16T22:05:37Z

On Wed, Aug 16, 2017 at 11:55 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Wed, Aug 16, 2017 at 2:45 PM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
>>
>> But it would be good to just test this in general too, and make sure I
>> didn't screw up some reference count or something. The patch *looks*
>> obviously correct, but ...
>
> Side note: I suspect it should be marked for stable, but it's going to
> be basically impossible to back-port this any further than 4.7 or
> something where we made each pts mount its own proper filesystem. The
> code before that was a mess, and this is never going to work right in
> old kernels.

Yeah, it would be nice if this could make it into stable at least and of course
into 4.13 but I take it that's a given anyway.

>
> Of course, TIOCGPTPEER itself is much more recent than that and was
> done in this merge window, so hopefully you haven't backported it and
> expect this all to work in some older kernel?

No, I haven't backported anything and we never intended to.
Serge, Stéphane, and I were very careful to not blindly rely on anything
that recent and - imho - security sensitive in our api. I see this more as a
"tech-preview" until this has seen some decent userspace testing. Even
if the kernel side seems fine now a lot of the userspace pty api is currently
using path-based operations instead of operations on the pty fds themselves.
This is tricky and error-prone when sending around pty fds between
different namespaces as one can see from the ttyname{_r}() example above.

Christian