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 #include <arpa/inet.h>
90 struct sockaddr_un sun;
94 static struct sockaddr_un socket_sun;
95 static const char *const *executor_argv;
97 static void propagate_exit_status(int status, const char *what) {
100 if (WIFEXITED(status)) {
104 if (WIFSIGNALED(status)) {
105 int sig = WTERMSIG(status);
106 const char *signame = strsignal(sig);
107 if (signame == 0) signame = "unknown signal";
109 if (! WCOREDUMP(status) &&
116 sa.sa_handler = SIG_DFL;
117 r = sigaction(sig, &sa, 0);
118 if (r) diee("failed to reset signal handler while propagating %s",
123 sigaddset(&sset, sig);
124 r = sigprocmask(SIG_UNBLOCK, &sset, 0);
125 if (r) diee("failed to reset signal block while propagating %s",
129 die("unexpectedly kept running after raising (to propagate) %s",
133 die("%s failed due to signal %d %s%s", what, sig, signame,
134 WCOREDUMP(status) ? " (core dumped)" : "");
137 die("%s failed with weird wait status %d 0x%x", what, status, status);
140 static __attribute((noreturn)) void die_data_overflow(void) {
141 die("cannot handle data with length >2^32");
144 static void prepare_data(size_t *len, char **buf,
145 const void *data, size_t dl) {
147 if (dl >= SIZE_MAX - *len)
152 memcpy(*buf, data, dl);
157 static void prepare_length(size_t *len, char **buf, size_t dl_sz) {
158 if (dl_sz > UINT32_MAX) die_data_overflow();
159 uint32_t dl = htonl(dl_sz);
160 prepare_data(len, buf, &dl, sizeof(dl));
163 static void prepare_string(size_t *len, char **buf, const char *s) {
164 size_t sl = strlen(s);
165 prepare_data(len, buf, s, sl+1);
168 static void prepare_message(size_t *len, char **buf) {
171 const char *const *p = (void*)environ;
174 prepare_string(len, buf, s);
177 prepare_string(len, buf, "");
181 prepare_string(len, buf, s);
184 static void send_fd(FILE *call_sock, int payload_fd) {
185 int via_fd = fileno(call_sock);
188 struct cmsghdr align;
189 char buf[CMSG_SPACE(sizeof(payload_fd))];
199 iov.iov_base = &dummy_byte;
205 msg.msg_control = cmsg_buf.buf;
206 msg.msg_controllen = sizeof(cmsg_buf.buf);
208 struct cmsghdr *cmsg = CMSG_FIRSTHDR(&msg);
209 cmsg->cmsg_level = SOL_SOCKET;
210 cmsg->cmsg_type = SCM_RIGHTS;
211 cmsg->cmsg_len = CMSG_LEN(sizeof(payload_fd));
212 *(int*)CMSG_DATA(cmsg) = payload_fd;
214 msg.msg_controllen = sizeof(cmsg_buf.buf);
217 ssize_t r = sendmsg(via_fd, &msg, 0);
219 if (errno == EINTR) continue;
227 static void send_request(FILE *call_sock) {
228 // Sending these first makes it easier for the script to
229 // use buffered IO for the message.
230 send_fd(call_sock, 0);
231 send_fd(call_sock, 1);
232 send_fd(call_sock, 2);
235 prepare_message(&len, 0);
236 char *m = malloc(len);
237 if (!m) diee("failed to allocate for message");
239 prepare_length(0, &p, len - 4);
240 prepare_message(0, &p);
241 assert(p == m + len);
243 ssize_t sr = fwrite(p, len, 1, call_sock);
244 if (sr != 1) diee("write request");
247 static FILE *call_sock_from_fd(int fd) {
250 FILE *call_sock = fdopen(fd, "r+");
251 if (!call_sock) diee("fdopen socket");
253 r = setvbuf(call_sock, 0, _IONBF, 0);
254 if (r) die("setvbuf socket");
259 static bool was_eof(FILE *call_sock) {
260 return feof(call_sock) || errno==ECONNRESET;
263 // Returns: call(client-end), or 0 to mean "is garbage"
264 // find_socket_path must have been called
265 static FILE *connect_existing(void) {
270 fd = socket(AF_UNIX, SOCK_STREAM, 0);
271 if (fd==-1) diee("socket() for client");
273 socklen_t salen = sizeof(sun);
274 r = connect(fd, (const struct sockaddr*)&socket_sun, salen);
276 if (errno==ECONNREFUSED || errno==ENOENT) goto x_garbage;
277 diee("connect() %s", socket_path);
280 call_sock = call_sock_from_fd(fd);
284 size_t sr = fread(&ack, sizeof(ack), 1, call_sock);
286 if (was_eof(call_sock)) goto x_garbage;
287 diee("read() ack byte");
289 if (ack != '\n') die("got ack byte 0x%02x, not '\n'", ack);
291 // We're committed now, send the request (or bail out)
292 send_request(call_sock);
298 if (fd >= 0) close(fd);
302 static __attribute__((noreturn))
303 void become_setup(int sfd, int fake_pair[2]) {
305 int call_fd = fake_pair[1];
307 int fd0_save = dup(0); if (fd0_save < 0) diee("dup stdin");
308 int fd1_save = dup(1); if (fd1_save < 0) diee("dup stdin");
310 int null_0 = open("/dev/null", O_RDONLY); if (null_0 < 0) diee("open null");
311 if (dup2(null_0, 0)) diee("dup2 /dev/null onto stdin");
312 if (dup2(2, 1) != 1) die("dup2 stderr onto stdout");
314 putenv(m_asprintf("PREFORK_INTERP=%d,%d,%d,%d,%s",
315 sfd, call_fd, fd0_save, fd1_save, socket_path));
317 execvp(executor_argv[0], (char**)executor_argv);
318 diee("execute %s", executor_argv[0]);
321 static FILE *connect_or_spawn(void) {
324 FILE *call_sock = connect_existing();
325 if (call_sock) return call_sock;
327 int lockfd = acquire_lock();
328 call_sock = connect_existing();
329 if (call_sock) { close(lockfd); return call_sock; }
331 // We must start a fresh one, and we hold the lock
333 r = unlink(socket_path);
334 if (r<0) diee("failed to remove stale socket %s", socket_path);
337 r = socketpair(AF_UNIX, SOCK_STREAM, 0, fake_pair);
338 if (r<0) diee("socketpair() for fake initial connection");
340 int sfd = socket(AF_UNIX, SOCK_STREAM, 0);
341 if (sfd<0) diee("socket() for new listener");
343 socklen_t salen = sizeof(sun);
344 r= bind(sfd, (const struct sockaddr*)&socket_sun, salen);
345 if (r<0) diee("bind() on new listener");
347 // We never want callers to get ECONNREFUSED. But:
348 // There is a race here: from my RTFM they may get ECONNREFUSED
349 // if they try between our bind() and listen(). But if they do, they'll
350 // acquire the lock (serialising with us) and retry, and then it will work.
351 r = listen(sfd, INT_MAX);
352 if (r<0) diee("listen() for new listener");
354 pid_t setup_pid = fork();
355 if (setup_pid == (pid_t)-1) diee("fork for spawn setup");
356 if (!setup_pid) become_setup(sfd, fake_pair);
361 pid_t got = waitpid(setup_pid, &status, 0);
362 if (got == (pid_t)-1) diee("waitpid setup [%ld]", (long)setup_pid);
363 if (got != setup_pid) diee("waitpid setup [%ld] gave [%ld]!",
364 (long)setup_pid, (long)got);
365 if (status != 0) propagate_exit_status(status, "setup");
368 return call_sock_from_fd(fake_pair[0]);
371 static void make_executor_argv(const char *const *argv) {
373 #define EACH_NEW_ARG(EACH) { \
374 arg = interp; { EACH } \
375 if ((arg = script)) { EACH } \
376 const char *const *walk = argv; \
377 while ((arg = *walk++)) { EACH } \
381 EACH_NEW_ARG( (void)arg; count++; );
383 const char **out = calloc(count, sizeof(char*));
384 executor_argv = (const char* const*)out;
385 if (!executor_argv) diee("allocate for arguments");
387 EACH_NEW_ARG( *out++ = arg; );
391 int main(int argc_unused, const char *const *argv) {
398 // which ought to be passed on to the actual executor.
399 make_executor_argv(argv);
403 sun.sun_family = AF_UNIX;
404 assert(strlen(socket_path) <= sizeof(sun.sun_path));
405 strncpy(sun.sun_path, socket_path, sizeof(sun.sun_path));
407 FILE *call_sock = connect_or_spawn();
409 ssize_t sr = fread(&status, sizeof(status), 1, call_sock);
411 if (was_eof(call_sock)) die("per-call server monitor process quit");
412 diee("read status from call socket");
415 status = ntohl(status);
416 if (status > INT_MAX) die("status 0x%lx does not fit in an int",
417 (unsigned long)status);
419 propagate_exit_status(status, "invocation");