isatty() and errno

[Eric Blake]

Our assumption in ptsname.c is that isatty() will set errno on invalid 
fds.  But this is not required by POSIX, and indeed not enforced by 
Solaris 10; that is, our ptsname.c implementation was copied from glibc, 
and was making an assumption only guaranteed by glibc's implementation 
choice for isatty(), which ends up leaving errno unchanged when that 
code is compiled on Solaris.

But that means it is likely that other GNU code will assume isatty() 
sets errno.  Should we provide an isatty() module that guarantees that 
errno will be set when returning 0?  Or should I just patch ptsname.c to 
guarantee that errno is set without relying on isatty() to do the job?

--
Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library http://libvirt.org