chg: support long socket path

This patch replaces UNIX_PATH_MAX (108) with PATH_MAX (4096) so we can have
long unix path.

contrib/chg/chg.c

@@ -1,638 +1,638 b''
 /*
  * 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/file.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))
+#ifndef PATH_MAX
+#define PATH_MAX 4096
 #endif
 
 struct cmdserveropts {
-	char sockname[UNIX_PATH_MAX];
-	char initsockname[UNIX_PATH_MAX];
-	char redirectsockname[UNIX_PATH_MAX];
+	char sockname[PATH_MAX];
+	char initsockname[PATH_MAX];
+	char redirectsockname[PATH_MAX];
 	size_t argsize;
 	const char **args;
 };
 
 static void initcmdserveropts(struct cmdserveropts *opts) {
 	memset(opts, 0, sizeof(struct cmdserveropts));
 }
 
 static void freecmdserveropts(struct cmdserveropts *opts) {
 	free(opts->args);
 	opts->args = NULL;
 	opts->argsize = 0;
 }
 
 /*
  * Test if an argument is a sensitive flag that should be passed to the server.
  * Return 0 if not, otherwise the number of arguments starting from the current
  * one that should be passed to the server.
  */
 static size_t testsensitiveflag(const char *arg)
 {
 	static const struct {
 		const char *name;
 		size_t narg;
 	} flags[] = {
 		{"--config", 1},
 		{"--cwd", 1},
 		{"--repo", 1},
 		{"--repository", 1},
 		{"--traceback", 0},
 		{"-R", 1},
 	};
 	size_t i;
 	for (i = 0; i < sizeof(flags) / sizeof(flags[0]); ++i) {
 		size_t len = strlen(flags[i].name);
 		size_t narg = flags[i].narg;
 		if (memcmp(arg, flags[i].name, len) == 0) {
 			if (arg[len] == '\0') {
 				/* --flag (value) */
 				return narg + 1;
 			} else if (arg[len] == '=' && narg > 0) {
 				/* --flag=value */
 				return 1;
 			} else if (flags[i].name[1] != '-') {
 				/* short flag */
 				return 1;
 			}
 		}
 	}
 	return 0;
 }
 
 /*
  * Parse argv[] and put sensitive flags to opts->args
  */
 static void setcmdserverargs(struct cmdserveropts *opts,
 			     int argc, const char *argv[])
 {
 	size_t i, step;
 	opts->argsize = 0;
 	for (i = 0, step = 1; i < (size_t)argc; i += step, step = 1) {
 		if (!argv[i])
 			continue;  /* pass clang-analyse */
 		if (strcmp(argv[i], "--") == 0)
 			break;
 		size_t n = testsensitiveflag(argv[i]);
 		if (n == 0 || i + n > (size_t)argc)
 			continue;
 		opts->args = reallocx(opts->args,
 				      (n + opts->argsize) * sizeof(char *));
 		memcpy(opts->args + opts->argsize, argv + i,
 		       sizeof(char *) * n);
 		opts->argsize += n;
 		step = n;
 	}
 }
 
 static void preparesockdir(const char *sockdir)
 {
 	int r;
 	r = mkdir(sockdir, 0700);
 	if (r < 0 && errno != EEXIST)
 		abortmsgerrno("cannot create sockdir %s", sockdir);
 
 	struct stat st;
 	r = lstat(sockdir, &st);
 	if (r < 0)
 		abortmsgerrno("cannot stat %s", sockdir);
 	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];
+	char sockdir[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";
 	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->initsockname, sizeof(opts->initsockname),
 			"%s.%u", opts->sockname, (unsigned)getpid());
 	if (r < 0 || (size_t)r >= sizeof(opts->initsockname))
 		abortmsg("too long TMPDIR or CHGSOCKNAME (r = %d)", r);
 }
 
 static const char *gethgcmd(void)
 {
 	static const char *hgcmd = NULL;
 	if (!hgcmd) {
 		hgcmd = getenv("CHGHG");
 		if (!hgcmd || hgcmd[0] == '\0')
 			hgcmd = getenv("HG");
 		if (!hgcmd || hgcmd[0] == '\0')
 #ifdef HGPATH
 			hgcmd = (HGPATH);
 #else
 			hgcmd = "hg";
 #endif
 	}
 	return hgcmd;
 }
 
 static void execcmdserver(const struct cmdserveropts *opts)
 {
 	const char *hgcmd = gethgcmd();
 
 	const char *baseargv[] = {
 		hgcmd,
 		"serve",
 		"--cmdserver", "chgunix",
 		"--address", opts->initsockname,
 		"--daemon-postexec", "chdir:/",
 	};
 	size_t baseargvsize = sizeof(baseargv) / sizeof(baseargv[0]);
 	size_t argsize = baseargvsize + opts->argsize + 1;
 
 	const char **argv = mallocx(sizeof(char *) * argsize);
 	memcpy(argv, baseargv, sizeof(baseargv));
 	memcpy(argv + baseargvsize, opts->args, sizeof(char *) * opts->argsize);
 	argv[argsize - 1] = NULL;
 
 	if (putenv("CHGINTERNALMARK=") != 0)
 		abortmsgerrno("failed to putenv");
 	if (execvp(hgcmd, (char **)argv) < 0)
 		abortmsgerrno("failed to exec cmdserver");
 	free(argv);
 }
 
 /* Retry until we can connect to the server. Give up after some time. */
 static hgclient_t *retryconnectcmdserver(struct cmdserveropts *opts, pid_t pid)
 {
 	static const struct timespec sleepreq = {0, 10 * 1000000};
 	int pst = 0;
 
 	debugmsg("try connect to %s repeatedly", opts->initsockname);
 
 	unsigned int timeoutsec = 60;  /* default: 60 seconds */
 	const char *timeoutenv = getenv("CHGTIMEOUT");
 	if (timeoutenv)
 		sscanf(timeoutenv, "%u", &timeoutsec);
 
 	for (unsigned int i = 0; !timeoutsec || i < timeoutsec * 100; i++) {
 		hgclient_t *hgc = hgc_open(opts->initsockname);
 		if (hgc) {
 			debugmsg("rename %s to %s", opts->initsockname,
 					opts->sockname);
 			int r = rename(opts->initsockname, opts->sockname);
 			if (r != 0)
 				abortmsgerrno("cannot rename");
 			return hgc;
 		}
 
 		if (pid > 0) {
 			/* collect zombie if child process fails to start */
 			int r = waitpid(pid, &pst, WNOHANG);
 			if (r != 0)
 				goto cleanup;
 		}
 
 		nanosleep(&sleepreq, NULL);
 	}
 
 	abortmsg("timed out waiting for cmdserver %s", opts->initsockname);
 	return NULL;
 
 cleanup:
 	if (WIFEXITED(pst)) {
 		if (WEXITSTATUS(pst) == 0)
 			abortmsg("could not connect to cmdserver "
 				 "(exited with status 0)");
 		debugmsg("cmdserver exited with status %d", WEXITSTATUS(pst));
 		exit(WEXITSTATUS(pst));
 	} else if (WIFSIGNALED(pst)) {
 		abortmsg("cmdserver killed by signal %d", WTERMSIG(pst));
 	} else {
 		abortmsg("error while waiting for cmdserver");
 	}
 	return NULL;
 }
 
 /* Connect to a cmdserver. Will start a new server on demand. */
 static hgclient_t *connectcmdserver(struct cmdserveropts *opts)
 {
 	const char *sockname = opts->redirectsockname[0] ?
 		opts->redirectsockname : opts->sockname;
 	debugmsg("try connect to %s", sockname);
 	hgclient_t *hgc = hgc_open(sockname);
 	if (hgc)
 		return hgc;
 
 	/* prevent us from being connected to an outdated server: we were
 	 * told by a server to redirect to opts->redirectsockname and that
 	 * address does not work. we do not want to connect to the server
 	 * again because it will probably tell us the same thing. */
 	if (sockname == opts->redirectsockname)
 		unlink(opts->sockname);
 
 	debugmsg("start cmdserver at %s", opts->initsockname);
 
 	pid_t pid = fork();
 	if (pid < 0)
 		abortmsg("failed to fork cmdserver process");
 	if (pid == 0) {
 		execcmdserver(opts);
 	} else {
 		hgc = retryconnectcmdserver(opts, pid);
 	}
 
 	return hgc;
 }
 
 static void killcmdserver(const struct cmdserveropts *opts)
 {
 	/* resolve config hash */
 	char *resolvedpath = realpath(opts->sockname, NULL);
 	if (resolvedpath) {
 		unlink(resolvedpath);
 		free(resolvedpath);
 	}
 }
 
 static pid_t pagerpid = 0;
 static pid_t peerpgid = 0;
 static pid_t peerpid = 0;
 
 static void forwardsignal(int sig)
 {
 	assert(peerpid > 0);
 	if (kill(peerpid, sig) < 0)
 		abortmsgerrno("cannot kill %d", peerpid);
 	debugmsg("forward signal %d", sig);
 }
 
 static void forwardsignaltogroup(int sig)
 {
 	/* prefer kill(-pgid, sig), fallback to pid if pgid is invalid */
 	pid_t killpid = peerpgid > 1 ? -peerpgid : peerpid;
 	if (kill(killpid, sig) < 0)
 		abortmsgerrno("cannot kill %d", killpid);
 	debugmsg("forward signal %d to %d", sig, killpid);
 }
 
 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:
 	abortmsgerrno("failed to handle stop signal");
 }
 
 static void handlechildsignal(int sig UNUSED_)
 {
 	if (peerpid == 0 || pagerpid == 0)
 		return;
 	/* if pager exits, notify the server with SIGPIPE immediately.
 	 * otherwise the server won't get SIGPIPE if it does not write
 	 * anything. (issue5278) */
 	if (waitpid(pagerpid, NULL, WNOHANG) == pagerpid)
 		kill(peerpid, SIGPIPE);
 }
 
 static void setupsignalhandler(const hgclient_t *hgc)
 {
 	pid_t pid = hgc_peerpid(hgc);
 	if (pid <= 0)
 		return;
 	peerpid = pid;
 
 	pid_t pgid = hgc_peerpgid(hgc);
 	peerpgid = (pgid <= 1 ? 0 : pgid);
 
 	struct sigaction sa;
 	memset(&sa, 0, sizeof(sa));
 	sa.sa_handler = forwardsignaltogroup;
 	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_handler = forwardsignal;
 	sa.sa_flags |= SA_RESETHAND;
 	if (sigaction(SIGTERM, &sa, NULL) < 0)
 		goto error;
 
 	/* notify the worker about window resize events */
 	sa.sa_flags = SA_RESTART;
 	if (sigaction(SIGWINCH, &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;
 	/* get notified when pager exits */
 	sa.sa_handler = handlechildsignal;
 	sa.sa_flags = SA_RESTART;
 	if (sigaction(SIGCHLD, &sa, NULL) < 0)
 		goto error;
 
 	return;
 
 error:
 	abortmsgerrno("failed to set up signal handlers");
 }
 
 static void restoresignalhandler()
 {
 	struct sigaction sa;
 	memset(&sa, 0, sizeof(sa));
 	sa.sa_handler = SIG_DFL;
 	sa.sa_flags = SA_RESTART;
 	if (sigemptyset(&sa.sa_mask) < 0)
 		goto error;
 
 	if (sigaction(SIGHUP, &sa, NULL) < 0)
 		goto error;
 	if (sigaction(SIGTERM, &sa, NULL) < 0)
 		goto error;
 	if (sigaction(SIGWINCH, &sa, NULL) < 0)
 		goto error;
 	if (sigaction(SIGCONT, &sa, NULL) < 0)
 		goto error;
 	if (sigaction(SIGTSTP, &sa, NULL) < 0)
 		goto error;
 	if (sigaction(SIGCHLD, &sa, NULL) < 0)
 		goto error;
 
 	/* ignore Ctrl+C while shutting down to make pager exits cleanly */
 	sa.sa_handler = SIG_IGN;
 	if (sigaction(SIGINT, &sa, NULL) < 0)
 		goto error;
 
 	peerpid = 0;
 	return;
 
 error:
 	abortmsgerrno("failed to restore signal handlers");
 }
 
 /* This implementation is based on hgext/pager.py (post 369741ef7253)
  * Return 0 if pager is not started, or pid of the pager */
 static pid_t setuppager(hgclient_t *hgc, const char *const args[],
 		       size_t argsize)
 {
 	const char *pagercmd = hgc_getpager(hgc, args, argsize);
 	if (!pagercmd)
 		return 0;
 
 	int pipefds[2];
 	if (pipe(pipefds) < 0)
 		return 0;
 	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 pid;
 	} 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) {
 			abortmsgerrno("cannot start pager '%s'", pagercmd);
 		}
 		return 0;
 	}
 
 error:
 	close(pipefds[0]);
 	close(pipefds[1]);
 	abortmsgerrno("failed to prepare pager");
 	return 0;
 }
 
 static void waitpager(pid_t pid)
 {
 	/* close output streams to notify the pager its input ends */
 	fclose(stdout);
 	fclose(stderr);
 	while (1) {
 		pid_t ret = waitpid(pid, NULL, 0);
 		if (ret == -1 && errno == EINTR)
 			continue;
 		break;
 	}
 }
 
 /* Run instructions sent from the server like unlink and set redirect path
  * Return 1 if reconnect is needed, otherwise 0 */
 static int runinstructions(struct cmdserveropts *opts, const char **insts)
 {
 	int needreconnect = 0;
 	if (!insts)
 		return needreconnect;
 
 	assert(insts);
 	opts->redirectsockname[0] = '\0';
 	const char **pinst;
 	for (pinst = insts; *pinst; pinst++) {
 		debugmsg("instruction: %s", *pinst);
 		if (strncmp(*pinst, "unlink ", 7) == 0) {
 			unlink(*pinst + 7);
 		} else if (strncmp(*pinst, "redirect ", 9) == 0) {
 			int r = snprintf(opts->redirectsockname,
 					 sizeof(opts->redirectsockname),
 					 "%s", *pinst + 9);
 			if (r < 0 || r >= (int)sizeof(opts->redirectsockname))
 				abortmsg("redirect path is too long (%d)", r);
 			needreconnect = 1;
 		} else if (strncmp(*pinst, "exit ", 5) == 0) {
 			int n = 0;
 			if (sscanf(*pinst + 5, "%d", &n) != 1)
 				abortmsg("cannot read the exit code");
 			exit(n);
 		} else if (strcmp(*pinst, "reconnect") == 0) {
 			needreconnect = 1;
 		} else {
 			abortmsg("unknown instruction: %s", *pinst);
 		}
 	}
 	return needreconnect;
 }
 
 /*
  * Test whether the command is unsupported or not. This is not designed to
  * cover all cases. But it's fast, does not depend on the server and does
  * not return false positives.
  */
 static int isunsupported(int argc, const char *argv[])
 {
 	enum {
 		SERVE = 1,
 		DAEMON = 2,
 		SERVEDAEMON = SERVE | DAEMON,
 		TIME = 4,
 	};
 	unsigned int state = 0;
 	int i;
 	for (i = 0; i < argc; ++i) {
 		if (strcmp(argv[i], "--") == 0)
 			break;
 		if (i == 0 && strcmp("serve", argv[i]) == 0)
 			state |= SERVE;
 		else if (strcmp("-d", argv[i]) == 0 ||
 			 strcmp("--daemon", argv[i]) == 0)
 			state |= DAEMON;
 		else if (strcmp("--time", argv[i]) == 0)
 			state |= TIME;
 	}
 	return (state & TIME) == TIME ||
 	       (state & SERVEDAEMON) == SERVEDAEMON;
 }
 
 static void execoriginalhg(const char *argv[])
 {
 	debugmsg("execute original hg");
 	if (execvp(gethgcmd(), (char **)argv) < 0)
 		abortmsgerrno("failed to exec original hg");
 }
 
 int main(int argc, const char *argv[], const char *envp[])
 {
 	if (getenv("CHGDEBUG"))
 		enabledebugmsg();
 
 	if (!getenv("HGPLAIN") && isatty(fileno(stderr)))
 		enablecolor();
 
 	if (getenv("CHGINTERNALMARK"))
 		abortmsg("chg started by chg detected.\n"
 			 "Please make sure ${HG:-hg} is not a symlink or "
 			 "wrapper to chg. Alternatively, set $CHGHG to the "
 			 "path of real hg.");
 
 	if (isunsupported(argc - 1, argv + 1))
 		execoriginalhg(argv);
 
 	struct cmdserveropts opts;
 	initcmdserveropts(&opts);
 	setcmdserveropts(&opts);
 	setcmdserverargs(&opts, argc, argv);
 
 	if (argc == 2) {
 		if (strcmp(argv[1], "--kill-chg-daemon") == 0) {
 			killcmdserver(&opts);
 			return 0;
 		}
 	}
 
 	hgclient_t *hgc;
 	size_t retry = 0;
 	while (1) {
 		hgc = connectcmdserver(&opts);
 		if (!hgc)
 			abortmsg("cannot open hg client");
 		hgc_setenv(hgc, envp);
 		const char **insts = hgc_validate(hgc, argv + 1, argc - 1);
 		int needreconnect = runinstructions(&opts, insts);
 		free(insts);
 		if (!needreconnect)
 			break;
 		hgc_close(hgc);
 		if (++retry > 10)
 			abortmsg("too many redirections.\n"
 				 "Please make sure %s is not a wrapper which "
 				 "changes sensitive environment variables "
 				 "before executing hg. If you have to use a "
 				 "wrapper, wrap chg instead of hg.",
 				 gethgcmd());
 	}
 
 	setupsignalhandler(hgc);
 	pagerpid = setuppager(hgc, argv + 1, argc - 1);
 	int exitcode = hgc_runcommand(hgc, argv + 1, argc - 1);
 	restoresignalhandler();
 	hgc_close(hgc);
 	freecmdserveropts(&opts);
 	if (pagerpid)
 		waitpager(pagerpid);
 
 	return exitcode;
 }

tests/test-chg.t

@@ -1,86 +1,100 b''
 #require chg
 
   $ cp $HGRCPATH $HGRCPATH.orig
 
 init repo
 
   $ chg init foo
   $ cd foo
 
 ill-formed config
 
   $ chg status
   $ echo '=brokenconfig' >> $HGRCPATH
   $ chg status
   hg: parse error at * (glob)
   [255]
 
   $ cp $HGRCPATH.orig $HGRCPATH
+
+long socket path
+
+  $ sockpath=$TESTTMP/this/path/should/be/longer/than/one-hundred-and-seven/characters/where/107/is/the/typical/size/limit/of/unix-domain-socket
+  $ mkdir -p $sockpath
+  $ bakchgsockname=$CHGSOCKNAME
+  $ CHGSOCKNAME=$sockpath/server
+  $ export CHGSOCKNAME
+  $ chg root
+  $TESTTMP/foo
+  $ rm -rf $sockpath
+  $ CHGSOCKNAME=$bakchgsockname
+  $ export CHGSOCKNAME
+
   $ cd ..
 
 server lifecycle
 ----------------
 
 chg server should be restarted on code change, and old server will shut down
 automatically. In this test, we use the following time parameters:
 
  - "sleep 1" to make mtime different
  - "sleep 2" to notice mtime change (polling interval is 1 sec)
 
 set up repository with an extension:
 
   $ chg init extreload
   $ cd extreload
   $ touch dummyext.py
   $ cat <<EOF >> .hg/hgrc
   > [extensions]
   > dummyext = dummyext.py
   > EOF
 
 isolate socket directory for stable result:
 
   $ OLDCHGSOCKNAME=$CHGSOCKNAME
   $ mkdir chgsock
   $ CHGSOCKNAME=`pwd`/chgsock/server
 
 warm up server:
 
   $ CHGDEBUG= chg log 2>&1 | egrep 'instruction|start'
   chg: debug: start cmdserver at $TESTTMP/extreload/chgsock/server.* (glob)
 
 new server should be started if extension modified:
 
   $ sleep 1
   $ touch dummyext.py
   $ CHGDEBUG= chg log 2>&1 | egrep 'instruction|start'
   chg: debug: instruction: unlink $TESTTMP/extreload/chgsock/server-* (glob)
   chg: debug: instruction: reconnect
   chg: debug: start cmdserver at $TESTTMP/extreload/chgsock/server.* (glob)
 
 old server will shut down, while new server should still be reachable:
 
   $ sleep 2
   $ CHGDEBUG= chg log 2>&1 | (egrep 'instruction|start' || true)
 
 socket file should never be unlinked by old server:
 (simulates unowned socket by updating mtime, which makes sure server exits
 at polling cycle)
 
   $ ls chgsock/server-*
   chgsock/server-* (glob)
   $ touch chgsock/server-*
   $ sleep 2
   $ ls chgsock/server-*
   chgsock/server-* (glob)
 
 since no server is reachable from socket file, new server should be started:
 (this test makes sure that old server shut down automatically)
 
   $ CHGDEBUG= chg log 2>&1 | egrep 'instruction|start'
   chg: debug: start cmdserver at $TESTTMP/extreload/chgsock/server.* (glob)
 
 shut down servers and restore environment:
 
   $ rm -R chgsock
   $ CHGSOCKNAME=$OLDCHGSOCKNAME
   $ cd ..