NuttX has no real session/process-group abstraction, so the TTY layer
collapses the foreground process group onto the single dev->pid field
(pgrp == pid, one member per group). Extend the controlling-terminal
support so portable software (e.g. dropbear, socat) that relies on
job-control primitives works without losing the existing NuttX-specific
behaviour.
Driver (serial.c, pty.c):
- TIOCSCTTY now accepts a flag: arg > 0 keeps the historical "target
PID in arg" semantics (NSH registers the foreground command it just
spawned), while arg == 0 selects the calling task via
nxsched_getpid(), matching the POSIX flag convention used by
dropbear/socat/apue. This preserves all existing callers and makes
the previously-dead arg==0 path deliver SIGINT correctly.
- Add TIOCGPGRP/TIOCGSID (return dev->pid) and TIOCSPGRP (set it).
- pty.c gains the same handlers against pd_pid and includes
nuttx/sched.h for nxsched_getpid().
ioctl numbers (tioctl.h): TIOCGPGRP/TIOCSPGRP/TIOCGSID at 0x37-0x39.
libc wrappers:
- termios: tcgetpgrp(), tcsetpgrp(), tcgetsid() over the new ioctls.
- unistd: setsid()/getsid()/setpgid() stubs consistent with the
existing getpgrp()/getpgid() single-session model (sid == pgid ==
pid; setpgid only succeeds for pgid == pid).
Declare the new prototypes in unistd.h (tcgetsid was already in
termios.h) and register all sources in the Make.defs/CMakeLists.
Group-broadcast signalling (kill(-pgrp)) remains unsupported, so
tty signals still target the single dev->pid; a real session/process
group model is left as a follow-up.
Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>
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