Messages in this thread |  | | Date | Wed, 16 Aug 2017 21:48:07 +0200 | From | Christian Brauner <> | Subject | Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name |
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On Wed, Aug 16, 2017 at 11:48:48AM -0700, Linus Torvalds wrote: > On Wed, Aug 16, 2017 at 11:26 AM, Linus Torvalds > <torvalds@linux-foundation.org> wrote: > > > > Hardcoding "/dev/pts/%d" is something that user space can already do. > > The kernel can and should do better. > > Put another way: there's no point in applying the patch as-is, since > existing glibc ptsname() does the same thing better and faster > entirely in user space.
Right. I actually took that to be an argument for this patch not against it. :) Another point I was trying to make in my initial mail is that ttyname{_r}() will currently look at "/proc/self/fd/<nr> to detect the name of the associated pts device and it will error out if the content it reads is not a "/dev/pts/<n>" path. Afaict musl and glibc both currently rely on this. This would be broken with the current TIOCGPTPEER change.
> > Also, we already do special things to get a path for this, but it > clearly isn't working. See the > > /* We need to cache a fake path for TIOCGPTPEER. */ > > comment in ptmx_open(). Why doesn't the file d_path get filled in > correctly there, I wonder. > > Because The regular > > readlink("/proc/self/fd/0", ...) > > that 'tty' does works correctly. I think we've done something > incorrect in pty_open_peer(), which means that the fd path hasn't been > fully filled in. > > Fixing that *should* fix the readlink() automatically, since it > clearly works for the 'tty' binary. > > I'm wondering why it's not working as-is. "vfs_open()" does that > > file->f_path = *path; > > thing. Why aren't we getting the right path? The ptmx_open() code > looks ok to me.
I thought - and sorry if I'm completely wrong here - that the proc name came from the open(const char *pathname, ...) call. Currently the only way to retrieve a slave side fd for a given pty pair is by calling open("/dev/pts/<n>", O_RDWR | O_NOCTTY). This would take care of placing the correct path in the proc symlink through do_filp_open() and friends. However, for ioctl() calls that open dentries to return an fd this is not possible and - or so I thought - the proc name is/has to be generated via dynamic_dname(). But again, I might be totally off here.
Christian
> > Al, do you see what the issue is, and why we don't get a proper path > on that readlink? > > Linus
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