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/schfs/vfs.c

@@ -100,6 +100,7 @@ schfs_vfs_iload(struct inode *ip)
   ip->nlink     = in.nlink > 0x7fffffffu ? 0x7fffffff : (int)in.nlink;
   ip->size      = in.size;
   ip->rwmode    = RW;
+  ip->mode      = in.mode & 07777;   // 0 on disk: never recorded
   ip->supermode = 0;
   ip->showmode  = 1;
   ip->atime     = (uint)in.atime;
@@ -134,6 +135,8 @@ schfs_vfs_istore(struct inode *ip)
     in.mode = ip->type == T_DIR ? 0755 : 0644;
   }
 
+  if (ip->mode)
+    in.mode = ip->mode & 07777;
   in.type       = type_from_vfs(ip->type);
   in.rdev_major = (uint16_t)ip->major;
   in.rdev_minor = (uint16_t)ip->minor;