Pseudo-terminals, and what tmux and htop needed around them

- /dev/ptmx and /dev/pts/N: Unix98 pairs with a full line discipline,
  window sizes, job control and hangup (kernel/dev/pty.c).
- The console speaks scroll regions, insert/delete line, SU/SD, RI/IND/NEL,
  DECSC/DECRC; swallows charset designations and private CSI sequences;
  and LF only returns the carriage under ONLCR.
- setsid() drops the controlling terminal, so a pane's pty becomes its ctty.
- pipe2() honours O_NONBLOCK and O_CLOEXEC (libevent's signal pipe).
- File modes are stored and enforced: chmod, fchmod(at), umask, creation
  modes; /tmp is 1777.
- /proc/stat has real user/system/idle; /proc/<pid>/task; kthread flag.
- SO_PEERCRED, IOV_MAX 1024.
- /proc/strace: name a program and its syscalls go to the kernel log.
- World gains htop, btop, tmux, mc, ncdu, fastfetch, games, X toys, NetSurf.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4

kernel/fs/file.c

@@ -10,6 +10,7 @@
 #include "uapi/posix.h"
 #include "uapi/errno.h"
 #include "core/kmem.h"
+#include "dev/pty.h"
 
 extern struct devsw devsw[];
 
@@ -422,6 +423,10 @@ file_poll(struct file *f, int events)
       return rev;
     }
 
+    if(f->ip && f->ip->type == T_DEV &&
+       (f->ip->major == PTM_MAJOR || f->ip->major == PTS_MAJOR))
+      return pty_poll(f->ip, events, f->readable, f->writable);
+
     if(f->ip && f->ip->type == T_DEV && f->ip->major == CONSOLE){
       int rev = 0;
       if((events & POLLIN) && f->readable && console_input_ready(f->ip ? f->ip->minor : 1))