2 * "Interpreter" that you can put in #! like this
3 * #!/usr/bin/prefork-interp [<options>] <interpreter>
6 * prefork-interp [<option> ..] <interpreter> [<script> [<args> ...]]
7 * prefork-interp [<option>,..],<interpreter> <script> [<args> ...]
8 * prefork-interp '[<option> ..] <interpreter>' <script> [<args> ...]
12 * client (C wrapper) connects to server
13 * (including reading ack byte)
15 * === acquire lock ===
16 * makes new listening socket
17 * makes first-instance socketpair
18 * forks setup (script, sock fds indicated in env)
19 * fd0, fd1, fd2: from-outer-caller
20 * other fd: call(client-end)(fake)
21 * reaps setup (and reports error)
22 * (implicitly releases lock)
24 * setup (pre-exec) fd0: null,
25 * fd[12: fd2-from-outer-caller
26 * env fds: listener, call(server-end)(fake)
27 * env fds: orig-fd[01]
30 * setup (script) runs initialisation parts of the script
31 * at prefork establishment point:
32 * setup (pm) [1] opens syslog
36 # server (pm) [1] [fd0: null],
37 * [fd[12: fd2-from-outer-caller]
38 * right away, forks one fa-monitor
39 * [2] closes outer caller fds and call(fake)
40 * [server (pm)] fd[012]: null
41 * other fds: listener, syslog
42 * runs in loop accepting and forking,
43 * reaping and limiting children (incl fa-monitor)
44 * reports failures of monitors to syslog
46 * f-a monitor forks executor
48 * [fd[12: fd2-from-outer-caller]
49 * [other fds: call(server-end)(fake), syslog]
50 * runs as monitor, below
53 * [client (C wrapper)] if client connect succeeds:
54 * now fd: call(client-end)
55 * sends message with: cmdline, env
58 * [server (script)] accepts, forks monitor
60 * monitor [1] [fd[012]: null]
61 * other fds: syslog, call(server-end)
63 * receives args, env, fds
66 * executor sorts out fds:
67 * fd0, fd1, fd2: from-outer-caller
68 * close fds: call(server-end)
69 * retained fds: syslog
72 * runs main part of script
75 * [monitor] [fd[012]: null]
76 * [other fds: call(server-end), syslog]
78 * reports status via socket
80 * [client (C wrapper)] [fd0, fd1, fd2: from-outer-caller]
81 * [other fd: call(client-end)]
82 * receives status, exits appropriately
83 * (if was bad signal, reports to stderr, exits 127)
86 struct sockaddr_un sun;
90 static struct sockaddr_unix socket_sun;
91 static const char *const *executor_argv;
93 static void propagate_exit_status(int status, const char *what) {
96 if (WIFEXITED(status)) {
100 if (WIFSIGNALED(status)) {
101 int sig = WTERMSIG(status);
102 char *signame = strsignal(sig);
103 if (signame == 0) signame = "unknown signal";
105 if (! WCOREDUMP(status) &&
112 sa.sa_handler = SIG_DFL;
113 r = sigaction(sig, &sa, 0);
114 if (r) diee("failed to reset signal handler while propagating %s",
119 sigaddset(&sset, sig);
120 r = sigprocmask(SA_UNBLOCK, sset, 0);
121 if (r) diee("failed to reset signal block while propagating %s",
125 die("unexpectedly kept running after raising (to propagate) %s",
129 die("setup failed due to signal %d %s%s", sig, signame,
130 WCOREDUMP(status) ? " (core dumped)" : "");
133 die("setup failed with weird wait status %d 0x%x", status, status);
136 static void die_data_overflow __attribute((noreturn)) {
137 die("cannot handle data with length >2^32");
140 static void prepare_data(size_t *len, char **buf,
141 const void *data, size_t dl) {
143 if (dl >= SIZE_MAX - *len)
148 memcpy(*buf, data, dl);
153 static void prepare_length(size_t *len, char **buf, size_t dl) {
154 if (dl > UINT32_MAX) die_data_overflow();
155 uint32_t dl = htonl(dl);
156 prepare_data(len, buf, &dl, sizeof(dl));
159 static void prepare_string(size_t *len, char **buf, const char *string) {
160 size_t sl = strlen(s);
161 prepare_data(len, buf, s, sl+1);
164 static void prepare_message(size_t *len, char **buf) {
167 const char *const *p = environ;
170 prepare_string(len, buf, s);
173 prepare_string(len, buf, "");
177 prepare_string(len, buf, s);
180 static void send_fd(int via_fd, int payload_fd) {
182 struct cmsghdr align;
183 char buf[CMSG_SPACE(sizeof(payload_fd))];
188 struct cmsghdr *cmsg = CMSG_FIRSTHDR(&msg);
189 cmsg->cmsg_level = SOL_SOCKET;
190 cmsg->cmsg_type = SCM_RIGHTS;
191 cmsg->cmsg_len = CMSG_LEN(sizeof(payload_fd));
192 *(int*)CMSG_DATA(cmsg) = payload_fd;
198 iov.iov_base = &dummy_byte;
204 msg.msg_control = msg.buf;
205 msg.msg_controllen = sizeof(msg.buf);
208 ssize_t r = sendmsg(via_fd, &msg, 0);
210 if (errno == EINTR) continue;
218 static void send_request(int call_fd, const char *const *argv) {
219 // Sending these first makes it easier for the script to
220 // use buffered IO for the message.
226 prepare_message(&len, 0, argv);
227 char *m = malloc(len);
228 if (!m) diee("failed to allocate for message");
230 prepare_length(0, &p, len - 4);
231 prepare_message(0, &p, argv);
232 assert(p == m + len);
236 ssize_t r = write(call_fd, p, len);
238 if (errno == EINTR) continue;
239 diee("write request");
248 // Returns: call(client-end) fd, or -1 to mean "is garbage"
249 // find_socket_path must have been called
250 static int connect_existing(void) {
254 bool isgarbage = check_garbage();
255 if (isgarbage) goto x_garbage;
257 fd = socket(AF_UNIX, SOCK_STREAM, 0);
258 if (fd==-1) diee("socket() for client");
260 salen_t salen = sizeof(sun);
261 r = connect(client, (const struct sockaddr*)&socket_sun, salen);
263 if (errno==ECONNREFUSED || errno==ENOENT) goto x_garbgae;
264 diee("connect() %s", socket_path);
269 sr = read(fd, &ack, 1);
271 if (errno==ECONNRESET) goto x_garbage;
272 if (errno==EINTR) continue;
273 diee("read() ack byte");
275 if (sr == 0) { goto x_garbage; }
276 if (ack != '\n') die("got ack byte 0x%02x, not '\n'", ack);
280 // We're committed now, send the request (or bail out)
281 send_request(call, argv);
286 if (fd >= 0) close(fd);
290 static void become_setup(int sfd, int fake_pair[2])
291 __attribute__((noreturn))
294 int call_fd = fake_pair[1];
296 int fd0_save = dup(0); if (fd0_save < 0) diee("dup stdin");
297 int fd1_save = dup(1); if (fd1_save < 0) diee("dup stdin");
299 int null_0 = open("/dev/null", O_RDONLY); if (null_0 < 0) diee("open null");
300 if (dup2(null_0, 0)) diee("dup2 /dev/null onto stdin");
301 if (dup2(2, 1) != 1) die("dup2 stderr onto stdout");
303 putenv(asprintf("PREFORK_INTERP=%d,%d,%d,%d,%s",
304 sfd, call_fd, fd0_save, fd1_save, socket_path));
306 execvp(executor_argv[0], executor_argv);
307 diee("execute %s", executor_argv[0]);
310 static int connect_or_spawn(void) {
311 int fd = connect_existing();
312 if (fd >= 0) return fd;
314 int lockfd = acquire_lock();
315 fd = connect_existing();
316 if (fd >= 0) { close(lockfd); return fd; }
318 // We must start a fresh one, and we hold the lock
320 r = unlink(socketpath);
321 if (r<0) diee("failed to remove stale socket %s", socketpath);
324 r = socketpair(AF_UNIX, SOCK_STREAM, 0, fake_pair);
325 if (r<0) diee("socketpair() for fake initial connection");
327 int sfd = socket(AF_UNIX, SOCK_STREAM, 0);
328 if (sfd<0) diee("socket() for new listener");
330 salen_t salen = sizeof(sun);
331 r= bind(sfd, (const struct sockaddr*)&socket_sun, saledn);
332 if (r<0) diee("bind() on new listener");
334 // We never want callers to get ECONNREFUSED!.
335 // There is a race here: from my RTFM they may get ECONNREFUSED
336 // if they tr between our bind() and listen(). But if they do, they'll
337 // acquire the lock (serialising with us) and retry, and then it will work.
338 r = listen(sfd, INT_MAX);
339 if (r<0) diee("listen() for new listener");
341 pid_t setup_pid = fork();
342 if (setup_pid == (pid_t)-1) diee("fork for spawn setup");
343 if (!setup_pid) become_setup(sfd, fake_pair);
348 pid_t got = waitpid(setup_pid, &status, 0);
349 if (got == (pid_t)-1) diee("waitpid setup [%ld]", (long)setup_pid);
350 if (got != setup_pid) diee("waitpid setup [%ld] gave [%ld]!",
351 (long)setup_pid, (long)got);
352 if (status != 0) propagate_exit_status(status);
358 static void make_executor_argv(const char *const *argv) {
359 #define EACH_NEW_ARGV(EACH) { \
360 arg = interp; { EACH } \
361 if ((arg = script)) { EACH } \
362 const char *const *walk = argv; \
363 while ((arg = *walk++)) { EACH } \
367 MAKE_NEW_ARGV( (void)arg; count++; );
369 executor_argv = calloc(count, sizeof(char*));
370 if (!executor_argv) diee("allocate for arguments");
372 char **out = executor_argv;
373 MAKE_NEW_ARGV( *out++ = arg; );
377 int main(int argc_unused, const char *const *argv) {
384 // which ought to be passed on to the actual executor.
385 make_executor_argv(argv);
389 sun.sun_family = AF_UNIX;
390 assert(strlen(socket_path) <= sizeof(sun.sun_path));
391 strncpy(sun.sun_path, socket_path, sizeof(sun.sun_path));
393 int call_fd = connect_or_spawn();