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

include/core/defs.h

@@ -61,6 +61,10 @@ int             pciuser_mmio_ok(uint64 phys, uint64 len);
 void            pciuser_release_all(struct proc*);
 int             pciuser_owner_pid(int idx);
 int             proc_reincarnate(int status);
+void            proc_cputime(uint64 *user, uint64 *sys);
+// kernel/dev/procfs.c: /proc/strace
+int             strace_wanted(const char *name);
+int             proc_write_strace(int user_src, uint64 src, uint n);
 void            proc_kill_init(void);
 extern uint     init_generation;
 void            cprintf(char*, ...);
@@ -512,6 +516,7 @@ int             socksendto(struct socket*, char *buf, int n,
 int             sockbind_in(struct socket*, uint addr, ushort port);
 int             sockconnect_in(struct socket*, uint addr, ushort port);
 int             sock_domain(struct socket*);
+int             sock_peercred(struct socket*, int*, uint*, uint*);
 // Socket options. The syscall layer does the user-memory marshalling and these
 // do the work, because struct socket's fields live in kernel/net/unix.c and the
 // syscall layer deliberately cannot see them.

include/core/param.h

@@ -29,7 +29,7 @@
 #define NOFILE       128  // open files per process
 #define NFILE        512  // open files per system
 #define NINODE       200  // maximum number of active i-nodes
-#define NDEV          13  // maximum major device number
+#define NDEV          16  // maximum major device number
 #define RAMDISK_DEV    2  // memory-backed block device (kernel/dev/ramdisk.c)
 #define USBDISK_DEV    3  // USB mass storage (kernel/drivers/usb_storage.c)
 

include/core/proc.h

@@ -174,6 +174,7 @@ struct procinfo {
   uint64 nvcsw, nivcsw;     // voluntary / involuntary context switches
   char   name[16];
   char   exe[64];           // full path, for /proc/<pid>/exe
+  int    kthread;           // a kernel thread, not a program
 };
 
 struct proc {
@@ -321,6 +322,14 @@ struct proc {
   // chroot(2): where an absolute path starts, and where ".." stops. 0 is the
   // system's root. Inherited across fork, held as a reference like cwd.
   struct inode *root;
+
+  // Syscall tracing: every call and its result go to the log. Set by exec
+  // when the program's name is the one written to /proc/strace, and kept
+  // across fork so that what a traced program starts is traced too.
+  int strace;
+
+  // umask(2). Inherited across fork; 022 for the first process.
+  uint umask;
 };
 #define FD_CLOEXEC 1
 

include/dev/pty.h

@@ -0,0 +1,41 @@
+#pragma once
+
+// Pseudo-terminals, Unix98 style: open /dev/ptmx and get the master side of a
+// new pair; the slave is /dev/pts/N. What sits between the two is the same
+// line discipline a console has. See kernel/dev/pty.c.
+
+#include "core/types.h"
+
+#define PTMX_MAJOR  13      // /dev/ptmx: opening it allocates a pair
+#define PTM_MAJOR   14      // a master, minor = pair number; never in a listing
+#define PTS_MAJOR   15      // /dev/pts/N
+#define NPTY        32
+
+// A controlling terminal that is a pty, in proc->ctty: PTY_CTTY + N. The
+// console's are 1..NVT.
+#define PTY_CTTY    64
+
+struct inode;
+struct file;
+
+int  pty_alloc(void);                // the new pair's number, or -1
+int  pty_used(int n);
+int  pty_ioctl(struct inode *ip, uint request, addr_t arg);
+int  pty_poll(struct inode *ip, int events, int readable, int writable);
+struct inode *ptmx_open(struct inode *ip);  // ip locked; returns the master, locked
+void pty_init(void);
+
+// Lines the devsw table needs.
+int  ptm_read(struct inode*, uint64, char*, int);
+int  ptm_write(struct inode*, uint64, char*, int);
+int  ptm_ready(struct inode*);
+void ptm_open(struct inode*);
+void ptm_close(struct inode*);
+int  pts_read(struct inode*, uint64, char*, int);
+int  pts_write(struct inode*, uint64, char*, int);
+int  pts_ready(struct inode*);
+void pts_open(struct inode*);
+void pts_close(struct inode*);
+
+// From kernel/fs/devfs.c: the inode of master N.
+struct inode *devfs_pty_master(int n);

include/dev/vt.h

@@ -82,7 +82,7 @@ struct vtcell {
 // Escape parser states. E_OSC and E_OSC_ESC exist for hyperlinks: a terminal
 // that does not follow OSC 8 must still consume it, or the URL is printed as
 // text. See the comment in kernel/core/console.c that this came from.
-enum { VE_NORMAL, VE_ESC, VE_CSI, VE_OSC, VE_OSC_ESC };
+enum { VE_NORMAL, VE_ESC, VE_CSI, VE_OSC, VE_OSC_ESC, VE_CHARSET };
 
 struct vt {
   int  index;                       // 0-based; /dev/tty<index+1>
@@ -98,6 +98,10 @@ struct vt {
   // CR, LF, backspace, an escape sequence -- clears it.
   int  wrap_pending;
   int  saved_cx, saved_cy;          // DECSC/DECRC
+  // The scrolling region, DECSTBM: rows scroll_top..scroll_bot inclusive.
+  // scroll_bot 0 means unset, the whole screen -- which keeps a grid resized
+  // underneath it from holding a stale bottom.
+  int  scroll_top, scroll_bot;
 
   uint8 fg, bg;                     // current SGR colours
   int   bold;

include/fs/file.h

@@ -130,6 +130,10 @@ struct inode {
   uint64 size;
 
   uint rwmode;
+  // POSIX permission bits from a filesystem that keeps them, or 0 for one
+  // that does not, in which case stat makes some up from the type. Bit 18 set
+  // alone means a mode of 0000, which chmod can ask for.
+  uint mode;
   uint supermode;
   uint showmode;
   uint atime;

include/net/socket.h

@@ -355,6 +355,12 @@ struct socket {
   // the only side that can say when they have been delivered.
   struct scm_fds scm[NSCM];
   int            nscm;
+
+  // Who is at this end, for SO_PEERCRED on the other: the process that made
+  // the socket, or for the server's end of a connection, the one that made
+  // the listener -- which is what Linux records too.
+  int   cred_pid;
+  uint  cred_uid, cred_gid;
 };
 
 #endif