prefork-interp.c

   1 /*
   2  * "Interpreter" that you can put in #! like this
   3  *   #!/usr/bin/prefork-interp [<options>] <interpreter>
   4  */
   5
   6 /*
   7  * Process structure:
   8  *  client (C wrapper)        connects to server
   9  *                              (including reading ack byte)
  10  *                            if fails or garbage
  11  *                            === acquire lock ===
  12  *                               makes new listening socket
  13  *                               makes first-instance socketpair
  14  *                            forks setup (script, sock fds indicated in env)
  15  *                            fd0, fd1, fd2: from-outer-caller
  16  *                            other fd: call(client-end)(fake)
  17  *                            reaps setup (and reports error)
  18  *                            (implicitly releases lock)
  19  *
  20  *     setup (pre-exec)       fd0: null,
  21  *                            fd[12: fd2-from-outer-caller
  22  *                            env fds: orig-fd[01], listener,
  23  *                            env fds: call(server-end)(fake)
  24  *                            close fd: lockfile
  25  *
  26  *     setup (script)         runs initialisation parts of the script
  27  *                            at prefork establishment point:
  28  *                            forks to logger(1)
  29  *                            forks for server, now becomes like monitor below
  30  *                            exits
  31  *
  32  *         server (script)    fd0: null, fd[12]: syslog
  33  *                            other fds: orig-fd[01], listener,
  34  *                            other fds: call(server-end)(fake)
  35  *
  36  *                            right away, forks one fake-accepted monitor:
  37  *          f-a monitor       [fd0: null, fd[12]: syslgo]
  38  *                            other fds: call(server-end)(fake)
  39  *                            runs as monitor, below
  40  *
  41  *         [server (script)]  fd0: null, fd[12]: syslog
  42  *                            other fds: listener
  43  *                            closes fds: orig-fd[01], call(server-end)fake)
  44  *                            runs in loop accepting and forking,
  45  *                            reaping and limiting children
  46  *                            reports failures of monitors to syslog
  47  *
  48  *  [client (C wrapper)]      if client connect succeeds:
  49  *                            now fd: call(client-end)
  50  *                               sends message with: cmdline, env
  51  *                               sends fds
  52  *
  53  *        [server (script)]   accepts, forks monitor
  54  *
  55  *          monitor           [fd0: null, fd[12]: syslgo]
  56  *                            other fds: call(server-end)
  57  *                            sends ack byte
  58  *                            receives args, env, fds
  59  *                            forks executor
  60  *
  61  *            executor        sorts out fds:
  62  *                            fd0, fd1, fd2: from-outer-caller
  63  *                            close fds: call(server-end)
  64  *                            implicitly closed fds: syslog
  65  *
  66  *                            sets cmdline, env
  67  *                            runs main part of script
  68  *                            exits normally
  69  *
  70  *          [monitor]         [fd0: null, fd[12]: syslgo]
  71  *                            [other fds: call(server-end)]
  72  *                            reaps executor
  73  *                            reports status via socket
  74  *
  75  *    [client (C wrapper)]    [fd0, fd1, fd2: from-outer-caller]
  76  *                            [other fd: call(client-end)]
  77  *                            receives status, exits appropriately
  78  *                            (if was bad signal, reports to stderr, exits 127)
  79  */
  80
  81 struct sockaddr_un sun;
  82
  83 #define ACK_BYTE '\n'
  84
  85 // Returns: call(client-end) fd, or -1 to mean "is garbage"
  86 // find_socket_path must have been called
  87 static int attempt_connect_existing(void) {
  88   int r;
  89   int fd = -1;
  90
  91   FILLZERO(sun);
  92   sun.sun_family = AF_UNIX;
  93   assert(strlen(socket_path) <= sizeof(sun.sun_path));
  94   strncpy(sun.sun_path, socket_path, sizeof(sun.sun_path));
  95
  96   bool isgarbage = check_garbage();
  97   if (isgarbage) goto x_garbage;
  98
  99   fd = socket(AF_UNIX, SOCK_STREAM, 0);
 100   if (fd==-1) diee("socket() for client");
 101
 102   salen_t salen = sizeof(sun);
 103   r = connect(client, (const struct sockaddr*)sun, salen);
 104   if (r==-1) {
 105     if (errno==ECONNREFUSED || errno==ENOENT) goto x_garbgae;
 106     diee("connect() %s", socket_path);
 107   }
 108
 109   for (;;) {
 110     char ack;
 111     sr = read(fd, &ack, 1);
 112     if (sr == -1) {
 113       if (errno==ECONNRESET) goto x_garbage;
 114       if (errno==EINTR) continue;
 115       diee("read() ack byte");
 116     }
 117     if (sr == 0) { goto x_garbage; }
 118     if (ack != '\n') die("got ack byte 0x%02x, not '\n'", ack);
 119     return fd;
 120   }
 121
 122  x_garbage:
 123   if (fd >= 0) close(fd);
 124   return -1;
 125 }
 126
 127 static int connect_or_spawn(void) {
 128   int fd = connect_existing();
 129   if (fd >= 0) return fd;
 130
 131   let acquire_lock();
 132     fd = connect_existing();
 133
 134 int main(int argc, const char *const *argv) {
 135   script = process_opts(argc, argv);
 136
 137   find_socket_path();
 138   int fd = connect_or_spawn();
 139 }