deprecated TIOCSPGRP and TIOCGPGRP ioctl command

[Peter Wemm]

On Wed, Nov 9, 2011 at 5:52 PM, Garrett Cooper <yanegomi at gmail.com> wrote:
> On Nov 9, 2011, at 4:49 PM, Peter Wemm wrote:
>
>> On Wed, Nov 9, 2011 at 3:39 PM, Giovanni Trematerra <gianni at freebsd.org> wrote:
>>> Are they deprecated enough to be removed, now?
>>> FYI FIFO doesn't support them.
>>>
>>> --
>>> Gianni
>>>
>>> =================================
>>> --- sys/kern/sys_pipe.c (revision 227233)
>>> +++ sys/kern/sys_pipe.c (working copy)
>>> @@ -1304,17 +1304,6 @@ pipe_ioctl(fp, cmd, data, active_cred, td)
>>>        *(int *)data = fgetown(&mpipe->pipe_sigio);
>>>        break;
>>>
>>> -   /* This is deprecated, FIOSETOWN should be used instead. */
>>> -   case TIOCSPGRP:
>>> -       PIPE_UNLOCK(mpipe);
>>> -       error = fsetown(-(*(int *)data), &mpipe->pipe_sigio);
>>> -       goto out_unlocked;
>>> -
>>> -   /* This is deprecated, FIOGETOWN should be used instead. */
>>> -   case TIOCGPGRP:
>>> -       *(int *)data = -fgetown(&mpipe->pipe_sigio);
>>> -       break;
>>> -
>>>    default:
>>>        error = ENOTTY;
>>
>> Be very very careful with this.  It's part of the classic BSD job
>> control API.  It would be wise to survey whether any ports shells use
>> this.
>>
>> You might also want to consider things like this in libc:
>> int
>> tcsetpgrp(int fd, pid_t pgrp)
>> {
>>        int s;
>>
>>        s = pgrp;
>>        return (_ioctl(fd, TIOCSPGRP, &s));
>> }
>> Our own libc code uses this, albeit on an API intended to be used on a tty.
>>
>> The shell I'd be most concerned about is csh/tcsh in our tree. It has
>> quite an #ifdef legacy layer and I couldn't convince myself it wasn't
>> using this indirectly (or the tc* functions) on pipes.
>>
>> It might also be an idea to see if the linux compat layer can be
>> switched over to using the newer API.
>
> Move to a compat library perhaps?
> -Garrett

It's not a compat library candidate.

Summary of the issue:
ioctl(fd, TIOCSPGRP, arg) can be used on sockets, pipes, ttys.  But not fifos.
this is a classic BSD job control API.
libc itself uses this internally on ttys.
libc doesn't check that the function that does this is actually a tty,
it could be being used by shells and pipes as an obscure side effect.
The API is equivalent to FIOSETOWN etc and sockets and pipes use
common code to implement both ioctl() calls.

The proposed patch was to remove the TIOCSPGRP -> FIOSETOWN mapping
for pipes only, to sync them with fifos.  ttys and sockets would be
unaffected.

The implementation function still has to stay.  Its not a large chunk
of obsolete code that goes away, its just the mapping between the
ioctl number and the implementation.

-- 
Peter Wemm - peter at wemm.org; peter at FreeBSD.org; peter at yahoo-inc.com; KI6FJV
"All of this is for nothing if we don't go to the stars" - JMS/B5
"If Java had true garbage collection, most programs would delete
themselves upon execution." -- Robert Sewell