Quoting Eric W. Biederman ([email protected]):
> Linus Torvalds <[email protected]> writes:
>
> > What this does is get rid of the horrible notion of having that
> >
> > struct inode *ptmx_inode
> >
> > be the interface between the pty code and devpts. By de-emphasizing the
> > ptmx inode, a lot of things actually get cleaner, and we will have a much
> > saner way forward.
>
> I will take a look in a minute. Before I do that I want to mention
> why I care about /dev/pts/ptmx.
>
> There is a posix function that is widely used called ptsname. It's
> function is to take a master file descriptor and returns the path to the
> slave.
>
> All we have in the kernel to support ptsname is an ioctl TIOCGPTN that
> returns the pty number in the appropriate instance of devpts.
>
> The only way we have today to query which instance of devpts the pty is
> on is through fstat and look st_dev to see if the file is on the correct
> filesystem. This works when /dev/pts/ptmx is used and fails when
> /dev/ptmx is used.
>
> Does anyone else care?
>
> If no one cares I will stop worrying about it and just get on with
> fixing the rest of this mess which there definitely seems to be the will
> to do.
There seem to be quite a few users of ptsname (as found by
codesearch.debian.net). I'm going to look through those results
a bit more tonight. One common idiom is
blah = ptsname(fd);
slavefd = open(blah, ...);
That's more easily solved with a new helper.
The scariest thing of course is any callers of ptsname which are setuid-root.
short answer: i'm going to do some research to try and answer "who cares".
-serge
