chg: forward job control signals to worker process (issue5051)

This is necessary to suspend/resume long pulls, interactive curses session,
etc.

The implementation is based on emacsclient, but our version doesn't test if
chg process is foreground or not before propagating SIGCONT. This is because
chg isn't always an interactive session. If we copy the SIGTTIN/SIGTTOU
emulation from emacsclient, non-interactive session can't be moved to a
background job.

  $ chg pull
  ^Z
  suspended
  $ bg %1
  [1] continued
  [1] suspended (tty input)  # wrong

https://github.com/emacs-mirror/emacs/blob/0e96320/lib-src/emacsclient.c#L1094

contrib/chg/chg.c

@@ -1,340 +1,383
 /*
  * A fast client for Mercurial command server
  *
  * Copyright (c) 2011 Yuya Nishihara <[e-mail]>
  *
  * This software may be used and distributed according to the terms of the
  * GNU General Public License version 2 or any later version.
  */
 
 #include <assert.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <sys/un.h>
 #include <sys/wait.h>
 #include <time.h>
 #include <unistd.h>
 
 #include "hgclient.h"
 #include "util.h"
 
 #ifndef UNIX_PATH_MAX
 #define UNIX_PATH_MAX (sizeof(((struct sockaddr_un *)NULL)->sun_path))
 #endif
 
 struct cmdserveropts {
 	char sockname[UNIX_PATH_MAX];
 	char lockfile[UNIX_PATH_MAX];
 	char pidfile[UNIX_PATH_MAX];
 };
 
 static void preparesockdir(const char *sockdir)
 {
 	int r;
 	r = mkdir(sockdir, 0700);
 	if (r < 0 && errno != EEXIST)
 		abortmsg("cannot create sockdir %s (errno = %d)",
 			 sockdir, errno);
 
 	struct stat st;
 	r = lstat(sockdir, &st);
 	if (r < 0)
 		abortmsg("cannot stat %s (errno = %d)", sockdir, errno);
 	if (!S_ISDIR(st.st_mode))
 		abortmsg("cannot create sockdir %s (file exists)", sockdir);
 	if (st.st_uid != geteuid() || st.st_mode & 0077)
 		abortmsg("insecure sockdir %s", sockdir);
 }
 
 static void setcmdserveropts(struct cmdserveropts *opts)
 {
 	int r;
 	char sockdir[UNIX_PATH_MAX];
 	const char *envsockname = getenv("CHGSOCKNAME");
 	if (!envsockname) {
 		/* by default, put socket file in secure directory
 		 * (permission of socket file may be ignored on some Unices) */
 		const char *tmpdir = getenv("TMPDIR");
 		if (!tmpdir)
 			tmpdir = "/tmp";
 		r = snprintf(sockdir, sizeof(sockdir), "%s/chg%d",
 			     tmpdir, geteuid());
 		if (r < 0 || (size_t)r >= sizeof(sockdir))
 			abortmsg("too long TMPDIR (r = %d)", r);
 		preparesockdir(sockdir);
 	}
 
 	const char *basename = (envsockname) ? envsockname : sockdir;
 	const char *sockfmt = (envsockname) ? "%s" : "%s/server";
 	const char *lockfmt = (envsockname) ? "%s.lock" : "%s/lock";
 	const char *pidfmt = (envsockname) ? "%s.pid" : "%s/pid";
 	r = snprintf(opts->sockname, sizeof(opts->sockname), sockfmt, basename);
 	if (r < 0 || (size_t)r >= sizeof(opts->sockname))
 		abortmsg("too long TMPDIR or CHGSOCKNAME (r = %d)", r);
 	r = snprintf(opts->lockfile, sizeof(opts->lockfile), lockfmt, basename);
 	if (r < 0 || (size_t)r >= sizeof(opts->lockfile))
 		abortmsg("too long TMPDIR or CHGSOCKNAME (r = %d)", r);
 	r = snprintf(opts->pidfile, sizeof(opts->pidfile), pidfmt, basename);
 	if (r < 0 || (size_t)r >= sizeof(opts->pidfile))
 		abortmsg("too long TMPDIR or CHGSOCKNAME (r = %d)", r);
 }
 
 /*
  * Make lock file that indicates cmdserver process is about to start. Created
  * lock file will be deleted by server. (0: success, -1: lock exists)
  */
 static int lockcmdserver(const struct cmdserveropts *opts)
 {
 	int r;
 	char info[32];
 	r = snprintf(info, sizeof(info), "%d", getpid());
 	if (r < 0 || (size_t)r >= sizeof(info))
 		abortmsg("failed to format lock info");
 	r = symlink(info, opts->lockfile);
 	if (r < 0 && errno != EEXIST)
 		abortmsg("failed to make lock %s (errno = %d)",
 			 opts->lockfile, errno);
 	return r;
 }
 
 static void execcmdserver(const struct cmdserveropts *opts)
 {
 	const char *hgcmd = getenv("CHGHG");
 	if (!hgcmd || hgcmd[0] == '\0')
 		hgcmd = getenv("HG");
 	if (!hgcmd || hgcmd[0] == '\0')
 		hgcmd = "hg";
 
 	const char *argv[] = {
 		hgcmd,
 		"serve",
 		"--cwd", "/",
 		"--cmdserver", "chgunix",
 		"--address", opts->sockname,
 		"--daemon-pipefds", opts->lockfile,
 		"--pid-file", opts->pidfile,
 		"--config", "extensions.chgserver=",
 		/* wrap root ui so that it can be disabled/enabled by config */
 		"--config", "progress.assume-tty=1",
 		NULL,
 	};
 	if (execvp(hgcmd, (char **)argv) < 0)
 		abortmsg("failed to exec cmdserver (errno = %d)", errno);
 }
 
 /*
  * Sleep until lock file is deleted, i.e. cmdserver process starts listening.
  * If pid is given, it also checks if the child process fails to start.
  */
 static void waitcmdserver(const struct cmdserveropts *opts, pid_t pid)
 {
 	static const struct timespec sleepreq = {0, 10 * 1000000};
 	int pst = 0;
 
 	for (unsigned int i = 0; i < 10 * 100; i++) {
 		int r;
 		struct stat lst;
 
 		r = lstat(opts->lockfile, &lst);
 		if (r < 0 && errno == ENOENT)
 			return;  /* lock file deleted by server */
 		if (r < 0)
 			goto cleanup;
 
 		if (pid > 0) {
 			/* collect zombie if child process fails to start */
 			r = waitpid(pid, &pst, WNOHANG);
 			if (r != 0)
 				goto cleanup;
 		}
 
 		nanosleep(&sleepreq, NULL);
 	}
 
 	abortmsg("timed out waiting for cmdserver %s", opts->lockfile);
 	return;
 
 cleanup:
 	if (pid > 0)
 		/* lockfile should be made by this process */
 		unlink(opts->lockfile);
 	if (WIFEXITED(pst)) {
 		abortmsg("cmdserver exited with status %d", WEXITSTATUS(pst));
 	} else if (WIFSIGNALED(pst)) {
 		abortmsg("cmdserver killed by signal %d", WTERMSIG(pst));
 	} else {
 		abortmsg("error white waiting cmdserver");
 	}
 }
 
 /* Spawn new background cmdserver */
 static void startcmdserver(const struct cmdserveropts *opts)
 {
 	debugmsg("start cmdserver at %s", opts->sockname);
 
 	if (lockcmdserver(opts) < 0) {
 		debugmsg("lock file exists, waiting...");
 		waitcmdserver(opts, 0);
 		return;
 	}
 
 	/* remove dead cmdserver socket if any */
 	unlink(opts->sockname);
 
 	pid_t pid = fork();
 	if (pid < 0)
 		abortmsg("failed to fork cmdserver process");
 	if (pid == 0) {
 		/* bypass uisetup() of pager extension */
 		int nullfd = open("/dev/null", O_WRONLY);
 		if (nullfd >= 0) {
 			dup2(nullfd, fileno(stdout));
 			close(nullfd);
 		}
 		execcmdserver(opts);
 	} else {
 		waitcmdserver(opts, pid);
 	}
 }
 
 static void killcmdserver(const struct cmdserveropts *opts, int sig)
 {
 	FILE *fp = fopen(opts->pidfile, "r");
 	if (!fp)
 		abortmsg("cannot open %s (errno = %d)", opts->pidfile, errno);
 	int pid = 0;
 	int n = fscanf(fp, "%d", &pid);
 	fclose(fp);
 	if (n != 1 || pid <= 0)
 		abortmsg("cannot read pid from %s", opts->pidfile);
 
 	if (kill((pid_t)pid, sig) < 0) {
 		if (errno == ESRCH)
 			return;
 		abortmsg("cannot kill %d (errno = %d)", pid, errno);
 	}
 }
 
 static pid_t peerpid = 0;
 
 static void forwardsignal(int sig)
 {
 	assert(peerpid > 0);
 	if (kill(peerpid, sig) < 0)
 		abortmsg("cannot kill %d (errno = %d)", peerpid, errno);
 	debugmsg("forward signal %d", sig);
 }
 
+static void handlestopsignal(int sig)
+{
+	sigset_t unblockset, oldset;
+	struct sigaction sa, oldsa;
+	if (sigemptyset(&unblockset) < 0)
+		goto error;
+	if (sigaddset(&unblockset, sig) < 0)
+		goto error;
+	memset(&sa, 0, sizeof(sa));
+	sa.sa_handler = SIG_DFL;
+	sa.sa_flags = SA_RESTART;
+	if (sigemptyset(&sa.sa_mask) < 0)
+		goto error;
+
+	forwardsignal(sig);
+	if (raise(sig) < 0)  /* resend to self */
+		goto error;
+	if (sigaction(sig, &sa, &oldsa) < 0)
+		goto error;
+	if (sigprocmask(SIG_UNBLOCK, &unblockset, &oldset) < 0)
+		goto error;
+	/* resent signal will be handled before sigprocmask() returns */
+	if (sigprocmask(SIG_SETMASK, &oldset, NULL) < 0)
+		goto error;
+	if (sigaction(sig, &oldsa, NULL) < 0)
+		goto error;
+	return;
+
+error:
+	abortmsg("failed to handle stop signal (errno = %d)", errno);
+}
+
 static void setupsignalhandler(pid_t pid)
 {
 	if (pid <= 0)
 		return;
 	peerpid = pid;
 
 	struct sigaction sa;
 	memset(&sa, 0, sizeof(sa));
 	sa.sa_handler = forwardsignal;
 	sa.sa_flags = SA_RESTART;
 	if (sigemptyset(&sa.sa_mask) < 0)
 		goto error;
 
 	if (sigaction(SIGHUP, &sa, NULL) < 0)
 		goto error;
 	if (sigaction(SIGINT, &sa, NULL) < 0)
 		goto error;
 
 	/* terminate frontend by double SIGTERM in case of server freeze */
 	sa.sa_flags |= SA_RESETHAND;
 	if (sigaction(SIGTERM, &sa, NULL) < 0)
 		goto error;
+
+	/* propagate job control requests to worker */
+	sa.sa_handler = forwardsignal;
+	sa.sa_flags = SA_RESTART;
+	if (sigaction(SIGCONT, &sa, NULL) < 0)
+		goto error;
+	sa.sa_handler = handlestopsignal;
+	sa.sa_flags = SA_RESTART;
+	if (sigaction(SIGTSTP, &sa, NULL) < 0)
+		goto error;
+
 	return;
 
 error:
 	abortmsg("failed to set up signal handlers (errno = %d)", errno);
 }
 
 /* This implementation is based on hgext/pager.py (pre 369741ef7253) */
 static void setuppager(hgclient_t *hgc, const char *const args[],
 		       size_t argsize)
 {
 	const char *pagercmd = hgc_getpager(hgc, args, argsize);
 	if (!pagercmd)
 		return;
 
 	int pipefds[2];
 	if (pipe(pipefds) < 0)
 		return;
 	pid_t pid = fork();
 	if (pid < 0)
 		goto error;
 	if (pid == 0) {
 		close(pipefds[0]);
 		if (dup2(pipefds[1], fileno(stdout)) < 0)
 			goto error;
 		if (isatty(fileno(stderr))) {
 			if (dup2(pipefds[1], fileno(stderr)) < 0)
 				goto error;
 		}
 		close(pipefds[1]);
 		hgc_attachio(hgc);  /* reattach to pager */
 		return;
 	} else {
 		dup2(pipefds[0], fileno(stdin));
 		close(pipefds[0]);
 		close(pipefds[1]);
 
 		int r = execlp("/bin/sh", "/bin/sh", "-c", pagercmd, NULL);
 		if (r < 0) {
 			abortmsg("cannot start pager '%s' (errno = %d)",
 				 pagercmd, errno);
 		}
 		return;
 	}
 
 error:
 	close(pipefds[0]);
 	close(pipefds[1]);
 	abortmsg("failed to prepare pager (errno = %d)", errno);
 }
 
 int main(int argc, const char *argv[], const char *envp[])
 {
 	if (getenv("CHGDEBUG"))
 		enabledebugmsg();
 
 	struct cmdserveropts opts;
 	setcmdserveropts(&opts);
 
 	if (argc == 2) {
 		int sig = 0;
 		if (strcmp(argv[1], "--kill-chg-daemon") == 0)
 			sig = SIGTERM;
 		if (strcmp(argv[1], "--reload-chg-daemon") == 0)
 			sig = SIGHUP;
 		if (sig > 0) {
 			killcmdserver(&opts, sig);
 			return 0;
 		}
 	}
 
 	hgclient_t *hgc = hgc_open(opts.sockname);
 	if (!hgc) {
 		startcmdserver(&opts);
 		hgc = hgc_open(opts.sockname);
 	}
 	if (!hgc)
 		abortmsg("cannot open hg client");
 
 	setupsignalhandler(hgc_peerpid(hgc));
 	hgc_setenv(hgc, envp);
 	setuppager(hgc, argv + 1, argc - 1);
 	int exitcode = hgc_runcommand(hgc, argv + 1, argc - 1);
 	hgc_close(hgc);
 	return exitcode;
 }