Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup

[H. Peter Anvin]

On April 9, 2016 6:09:09 AM PDT, One Thousand Gnomes <gnomes@xxxxxxxxxxxxxxxxxxx> wrote:
>
>> If anyone has a better idea on how userspace should connect the
>master
>> pty file descriptor the slave file descriptor, I would be willing to
>> implement that instead.
>
>If we are willing to go away from the existing mess of a tty interface
>inflicted on us by BSD and then mashed up by POSIX then a syscall of
>
>  int err = ptypair(int fd[2], int perms, int flags);
>
>[where flags is the O_ ones we usually need to cover (CLOEXEC etc) and
>maybe even some kind of "private" flag to say don't even expose it via
>devpts).
>
>would do remarkably sane things to the majoirty of use cases as it
>breaks
>the dependence on grantpt and also the historic screwup that pty pairs
>aren't allocated atomically with both file handles returned as pipe()
>does.
>
>Alan

We don't even need to do that if we'd be willing to change the user space interface... if we could rely on the POSIX interface then posix_openpt() could simply open /dev/pts/ptmx and everything would just work.

The trick here is how to make it work in the presence of some extremely bad practices in existing userspace.
-- 
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