[PATCH 2/2] openpty: use TIOCGPTPEER to open slave side fd

[Joseph Myers]

On Mon, 28 Aug 2017, Florian Weimer wrote:

> On 08/26/2017 03:44 PM, Christian Brauner wrote:
> > +#ifdef TIOCGPTPEER
> > +  slave = ioctl (master, TIOCGPTPEER, O_RDWR | O_NOCTTY);
> > +#else
> >    if (pts_name (master, &buf, sizeof (_buf)))
> >      goto fail;
> >  
> >    slave = open (buf, O_RDWR | O_NOCTTY);
> > +#endif
> 
> I don't think you can #ifdef out existing code this way without
> introducing failures on older kernels.  You need to try the ioctl first,
> and if that fails, use the old pts_name code.

And in principle there should be appropriate __ASSUME_* conditionals so 
that when building with a new-enough --enable-kernel the old code can be 
conditioned out (however, because this code is not Linux-specific, the old 
case would need to stay in the code even when __ASSUME_TIOCGPTPEER is 
defined unconditionally in the Linux kernel-features.h).

-- 
Joseph S. Myers
joseph@codesourcery.com