daemon.c - jrn/git - Git at Google

 #include "cache.h"
 #include "pkt-line.h"
 #include <signal.h>
 #include <sys/wait.h>
 #include <sys/socket.h>
 #include <netdb.h>
 #include <netinet/in.h>

 static const char daemon_usage[] = "git-daemon [--inetd | --port=n]";

 static int upload(char *dir, int dirlen)
 {
 	if (chdir(dir) < 0)
 		return -1;
 	chdir(".git");

 	/*
 	 * Security on the cheap.
 	 *
 	 * We want a readable HEAD, usable "objects" directory, and
 	 * a "git-daemon-export-ok" flag that says that the other side
 	 * is ok with us doing this.
 	 */
 	if (access("git-daemon-export-ok", F_OK) ||
 	    access("objects/00", X_OK) ||
 	    access("HEAD", R_OK))
 		return -1;

 	/*
 	 * We'll ignore SIGTERM from now on, we have a
 	 * good client.
 	 */
 	signal(SIGTERM, SIG_IGN);

 	/* git-upload-pack only ever reads stuff, so this is safe */
 	execlp("git-upload-pack", "git-upload-pack", ".", NULL);
 	return -1;
 }

 static int execute(void)
 {
 	static char line[1000];
 	int len;

 	len = packet_read_line(0, line, sizeof(line));

 	if (len && line[len-1] == '\n')
 		line[--len] = 0;

 	if (!strncmp("git-upload-pack /", line, 17))
 		return upload(line + 16, len - 16);

 	fprintf(stderr, "got bad connection '%s'\n", line);
 	return -1;
 }


 /*
  * We count spawned/reaped separately, just to avoid any
  * races when updating them from signals. The SIGCHLD handler
  * will only update children_reaped, and the fork logic will
  * only update children_spawned.
  *
  * MAX_CHILDREN should be a power-of-two to make the modulus
  * operation cheap. It should also be at least twice
  * the maximum number of connections we will ever allow.
  */
 #define MAX_CHILDREN 128

 static int max_connections = 25;

 /* These are updated by the signal handler */
 static volatile unsigned int children_reaped = 0;
 static pid_t dead_child[MAX_CHILDREN];

 /* These are updated by the main loop */
 static unsigned int children_spawned = 0;
 static unsigned int children_deleted = 0;

 static struct child {
 	pid_t pid;
 	socklen_t addrlen;
 	struct sockaddr_storage address;
 } live_child[MAX_CHILDREN];

 static void add_child(int idx, pid_t pid, struct sockaddr *addr, socklen_t addrlen)
 {
 	live_child[idx].pid = pid;
 	live_child[idx].addrlen = addrlen;
 	memcpy(&live_child[idx].address, addr, addrlen);
 }

 /*
  * Walk from "deleted" to "spawned", and remove child "pid".
  *
  * We move everything up by one, since the new "deleted" will
  * be one higher.
  */
 static void remove_child(pid_t pid, unsigned deleted, unsigned spawned)
 {
 	struct child n;

 	deleted %= MAX_CHILDREN;
 	spawned %= MAX_CHILDREN;
 	if (live_child[deleted].pid == pid) {
 		live_child[deleted].pid = -1;
 		return;
 	}
 	n = live_child[deleted];
 	for (;;) {
 		struct child m;
 		deleted = (deleted + 1) % MAX_CHILDREN;
 		if (deleted == spawned)
 			die("could not find dead child %d\n", pid);
 		m = live_child[deleted];
 		live_child[deleted] = n;
 		if (m.pid == pid)
 			return;
 		n = m;
 	}
 }

 /*
  * This gets called if the number of connections grows
  * past "max_connections".
  *
  * We _should_ start off by searching for connections
  * from the same IP, and if there is some address wth
  * multiple connections, we should kill that first.
  *
  * As it is, we just "randomly" kill 25% of the connections,
  * and our pseudo-random generator sucks too. I have no
  * shame.
  *
  * Really, this is just a place-holder for a _real_ algorithm.
  */
 static void kill_some_children(int signo, unsigned start, unsigned stop)
 {
 	start %= MAX_CHILDREN;
 	stop %= MAX_CHILDREN;
 	while (start != stop) {
 		if (!(start & 3))
 			kill(live_child[start].pid, signo);
 		start = (start + 1) % MAX_CHILDREN;
 	}
 }

 static void check_max_connections(void)
 {
 	for (;;) {
 		int active;
 		unsigned spawned, reaped, deleted;

 		spawned = children_spawned;
 		reaped = children_reaped;
 		deleted = children_deleted;

 		while (deleted < reaped) {
 			pid_t pid = dead_child[deleted % MAX_CHILDREN];
 			remove_child(pid, deleted, spawned);
 			deleted++;
 		}
 		children_deleted = deleted;

 		active = spawned - deleted;
 		if (active <= max_connections)
 			break;

 		/* Kill some unstarted connections with SIGTERM */
 		kill_some_children(SIGTERM, deleted, spawned);
 		if (active <= max_connections << 1)
 			break;

 		/* If the SIGTERM thing isn't helping use SIGKILL */
 		kill_some_children(SIGKILL, deleted, spawned);
 		sleep(1);
 	}
 }

 static void handle(int incoming, struct sockaddr *addr, socklen_t addrlen)
 {
 	pid_t pid = fork();

 	if (pid) {
 		unsigned idx;

 		close(incoming);
 		if (pid < 0)
 			return;

 		idx = children_spawned % MAX_CHILDREN;
 		children_spawned++;
 		add_child(idx, pid, addr, addrlen);

 		check_max_connections();
 		return;
 	}

 	dup2(incoming, 0);
 	dup2(incoming, 1);
 	close(incoming);
 	exit(execute());
 }

 static void child_handler(int signo)
 {
 	for (;;) {
 		pid_t pid = waitpid(-1, NULL, WNOHANG);

 		if (pid > 0) {
 			unsigned reaped = children_reaped;
 			dead_child[reaped % MAX_CHILDREN] = pid;
 			children_reaped = reaped + 1;
 			continue;
 		}
 		break;
 	}
 }

 static int serve(int port)
 {
 	struct addrinfo hints, *ai0, *ai;
 	int gai;
 	int socknum = 0, *socklist = NULL;
 	int maxfd = -1;
 	fd_set fds_init, fds;
 	char pbuf[NI_MAXSERV];

 	signal(SIGCHLD, child_handler);

 	sprintf(pbuf, "%d", port);
 	memset(&hints, 0, sizeof(hints));
 	hints.ai_family = AF_UNSPEC;
 	hints.ai_socktype = SOCK_STREAM;
 	hints.ai_protocol = IPPROTO_TCP;
 	hints.ai_flags = AI_PASSIVE;

 	gai = getaddrinfo(NULL, pbuf, &hints, &ai0);
 	if (gai)
 		die("getaddrinfo() failed: %s\n", gai_strerror(gai));

 	FD_ZERO(&fds_init);

 	for (ai = ai0; ai; ai = ai->ai_next) {
 		int sockfd;
 		int *newlist;

 		sockfd = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
 		if (sockfd < 0)
 			continue;
 		if (sockfd >= FD_SETSIZE) {
 			error("too large socket descriptor.");
 			close(sockfd);
 			continue;
 		}

 #ifdef IPV6_V6ONLY
 		if (ai->ai_family == AF_INET6) {
 			int on = 1;
 			setsockopt(sockfd, IPPROTO_IPV6, IPV6_V6ONLY,
 				   &on, sizeof(on));
 			/* Note: error is not fatal */
 		}
 #endif

 		if (bind(sockfd, ai->ai_addr, ai->ai_addrlen) < 0) {
 			close(sockfd);
 			continue;	/* not fatal */
 		}
 		if (listen(sockfd, 5) < 0) {
 			close(sockfd);
 			continue;	/* not fatal */
 		}

 		newlist = realloc(socklist, sizeof(int) * (socknum + 1));
 		if (!newlist)
 			die("memory allocation failed: %s", strerror(errno));

 		socklist = newlist;
 		socklist[socknum++] = sockfd;

 		FD_SET(sockfd, &fds_init);
 		if (maxfd < sockfd)
 			maxfd = sockfd;
 	}

 	freeaddrinfo(ai0);

 	if (socknum == 0)
 		die("unable to allocate any listen sockets on port %u", port);

 	for (;;) {
 		int i;
 		fds = fds_init;

 		if (select(maxfd + 1, &fds, NULL, NULL, NULL) < 0) {
 			if (errno != EINTR) {
 				error("select failed, resuming: %s",
 				      strerror(errno));
 				sleep(1);
 			}
 			continue;
 		}

 		for (i = 0; i < socknum; i++) {
 			int sockfd = socklist[i];

 			if (FD_ISSET(sockfd, &fds)) {
 				struct sockaddr_storage ss;
 				socklen_t sslen = sizeof(ss);
 				int incoming = accept(sockfd, (struct sockaddr *)&ss, &sslen);
 				if (incoming < 0) {
 					switch (errno) {
 					case EAGAIN:
 					case EINTR:
 					case ECONNABORTED:
 						continue;
 					default:
 						die("accept returned %s", strerror(errno));
 					}
 				}
 				handle(incoming, (struct sockaddr *)&ss, sslen);
 			}
 		}
 	}
 }

 int main(int argc, char **argv)
 {
 	int port = DEFAULT_GIT_PORT;
 	int inetd_mode = 0;
 	int i;

 	for (i = 1; i < argc; i++) {
 		char *arg = argv[i];

 		if (!strncmp(arg, "--port=", 7)) {
 			char *end;
 			unsigned long n;
 			n = strtoul(arg+7, &end, 0);
 			if (arg[7] && !*end) {
 				port = n;
 				continue;
 			}
 		}

 		if (!strcmp(arg, "--inetd")) {
 			inetd_mode = 1;
 			continue;
 		}

 		usage(daemon_usage);
 	}

 	if (inetd_mode)
 		return execute();

 	return serve(port);
 }
	#include "cache.h"
	#include "pkt-line.h"
	#include <signal.h>
	#include <sys/wait.h>
	#include <sys/socket.h>
	#include <netdb.h>
	#include <netinet/in.h>

	static const char daemon_usage[] = "git-daemon [--inetd \| --port=n]";

	static int upload(char *dir, int dirlen)
	{
	if (chdir(dir) < 0)
	return -1;
	chdir(".git");

	/*
	* Security on the cheap.
	*
	* We want a readable HEAD, usable "objects" directory, and
	* a "git-daemon-export-ok" flag that says that the other side
	* is ok with us doing this.
	*/
	if (access("git-daemon-export-ok", F_OK) \|\|
	access("objects/00", X_OK) \|\|
	access("HEAD", R_OK))
	return -1;

	/*
	* We'll ignore SIGTERM from now on, we have a
	* good client.
	*/
	signal(SIGTERM, SIG_IGN);

	/* git-upload-pack only ever reads stuff, so this is safe */
	execlp("git-upload-pack", "git-upload-pack", ".", NULL);
	return -1;
	}

	static int execute(void)
	{
	static char line[1000];
	int len;

	len = packet_read_line(0, line, sizeof(line));

	if (len && line[len-1] == '\n')
	line[--len] = 0;

	if (!strncmp("git-upload-pack /", line, 17))
	return upload(line + 16, len - 16);

	fprintf(stderr, "got bad connection '%s'\n", line);
	return -1;
	}


	/*
	* We count spawned/reaped separately, just to avoid any
	* races when updating them from signals. The SIGCHLD handler
	* will only update children_reaped, and the fork logic will
	* only update children_spawned.
	*
	* MAX_CHILDREN should be a power-of-two to make the modulus
	* operation cheap. It should also be at least twice
	* the maximum number of connections we will ever allow.
	*/
	#define MAX_CHILDREN 128

	static int max_connections = 25;

	/* These are updated by the signal handler */
	static volatile unsigned int children_reaped = 0;
	static pid_t dead_child[MAX_CHILDREN];

	/* These are updated by the main loop */
	static unsigned int children_spawned = 0;
	static unsigned int children_deleted = 0;

	static struct child {
	pid_t pid;
	socklen_t addrlen;
	struct sockaddr_storage address;
	} live_child[MAX_CHILDREN];

	static void add_child(int idx, pid_t pid, struct sockaddr *addr, socklen_t addrlen)
	{
	live_child[idx].pid = pid;
	live_child[idx].addrlen = addrlen;
	memcpy(&live_child[idx].address, addr, addrlen);
	}

	/*
	* Walk from "deleted" to "spawned", and remove child "pid".
	*
	* We move everything up by one, since the new "deleted" will
	* be one higher.
	*/
	static void remove_child(pid_t pid, unsigned deleted, unsigned spawned)
	{
	struct child n;

	deleted %= MAX_CHILDREN;
	spawned %= MAX_CHILDREN;
	if (live_child[deleted].pid == pid) {
	live_child[deleted].pid = -1;
	return;
	}
	n = live_child[deleted];
	for (;;) {
	struct child m;
	deleted = (deleted + 1) % MAX_CHILDREN;
	if (deleted == spawned)
	die("could not find dead child %d\n", pid);
	m = live_child[deleted];
	live_child[deleted] = n;
	if (m.pid == pid)
	return;
	n = m;
	}
	}

	/*
	* This gets called if the number of connections grows
	* past "max_connections".
	*
	* We _should_ start off by searching for connections
	* from the same IP, and if there is some address wth
	* multiple connections, we should kill that first.
	*
	* As it is, we just "randomly" kill 25% of the connections,
	* and our pseudo-random generator sucks too. I have no
	* shame.
	*
	* Really, this is just a place-holder for a _real_ algorithm.
	*/
	static void kill_some_children(int signo, unsigned start, unsigned stop)
	{
	start %= MAX_CHILDREN;
	stop %= MAX_CHILDREN;
	while (start != stop) {
	if (!(start & 3))
	kill(live_child[start].pid, signo);
	start = (start + 1) % MAX_CHILDREN;
	}
	}

	static void check_max_connections(void)
	{
	for (;;) {
	int active;
	unsigned spawned, reaped, deleted;

	spawned = children_spawned;
	reaped = children_reaped;
	deleted = children_deleted;

	while (deleted < reaped) {
	pid_t pid = dead_child[deleted % MAX_CHILDREN];
	remove_child(pid, deleted, spawned);
	deleted++;
	}
	children_deleted = deleted;

	active = spawned - deleted;
	if (active <= max_connections)
	break;

	/* Kill some unstarted connections with SIGTERM */
	kill_some_children(SIGTERM, deleted, spawned);
	if (active <= max_connections << 1)
	break;

	/* If the SIGTERM thing isn't helping use SIGKILL */
	kill_some_children(SIGKILL, deleted, spawned);
	sleep(1);
	}
	}

	static void handle(int incoming, struct sockaddr *addr, socklen_t addrlen)
	{
	pid_t pid = fork();

	if (pid) {
	unsigned idx;

	close(incoming);
	if (pid < 0)
	return;

	idx = children_spawned % MAX_CHILDREN;
	children_spawned++;
	add_child(idx, pid, addr, addrlen);

	check_max_connections();
	return;
	}

	dup2(incoming, 0);
	dup2(incoming, 1);
	close(incoming);
	exit(execute());
	}

	static void child_handler(int signo)
	{
	for (;;) {
	pid_t pid = waitpid(-1, NULL, WNOHANG);

	if (pid > 0) {
	unsigned reaped = children_reaped;
	dead_child[reaped % MAX_CHILDREN] = pid;
	children_reaped = reaped + 1;
	continue;
	}
	break;
	}
	}

	static int serve(int port)
	{
	struct addrinfo hints, ai0, ai;
	int gai;
	int socknum = 0, *socklist = NULL;
	int maxfd = -1;
	fd_set fds_init, fds;
	char pbuf[NI_MAXSERV];

	signal(SIGCHLD, child_handler);

	sprintf(pbuf, "%d", port);
	memset(&hints, 0, sizeof(hints));
	hints.ai_family = AF_UNSPEC;
	hints.ai_socktype = SOCK_STREAM;
	hints.ai_protocol = IPPROTO_TCP;
	hints.ai_flags = AI_PASSIVE;

	gai = getaddrinfo(NULL, pbuf, &hints, &ai0);
	if (gai)
	die("getaddrinfo() failed: %s\n", gai_strerror(gai));

	FD_ZERO(&fds_init);

	for (ai = ai0; ai; ai = ai->ai_next) {
	int sockfd;
	int *newlist;

	sockfd = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
	if (sockfd < 0)
	continue;
	if (sockfd >= FD_SETSIZE) {
	error("too large socket descriptor.");
	close(sockfd);
	continue;
	}

	#ifdef IPV6_V6ONLY
	if (ai->ai_family == AF_INET6) {
	int on = 1;
	setsockopt(sockfd, IPPROTO_IPV6, IPV6_V6ONLY,
	&on, sizeof(on));
	/* Note: error is not fatal */
	}
	#endif

	if (bind(sockfd, ai->ai_addr, ai->ai_addrlen) < 0) {
	close(sockfd);
	continue; /* not fatal */
	}
	if (listen(sockfd, 5) < 0) {
	close(sockfd);
	continue; /* not fatal */
	}

	newlist = realloc(socklist, sizeof(int) * (socknum + 1));
	if (!newlist)
	die("memory allocation failed: %s", strerror(errno));

	socklist = newlist;
	socklist[socknum++] = sockfd;

	FD_SET(sockfd, &fds_init);
	if (maxfd < sockfd)
	maxfd = sockfd;
	}

	freeaddrinfo(ai0);

	if (socknum == 0)
	die("unable to allocate any listen sockets on port %u", port);

	for (;;) {
	int i;
	fds = fds_init;

	if (select(maxfd + 1, &fds, NULL, NULL, NULL) < 0) {
	if (errno != EINTR) {
	error("select failed, resuming: %s",
	strerror(errno));
	sleep(1);
	}
	continue;
	}

	for (i = 0; i < socknum; i++) {
	int sockfd = socklist[i];

	if (FD_ISSET(sockfd, &fds)) {
	struct sockaddr_storage ss;
	socklen_t sslen = sizeof(ss);
	int incoming = accept(sockfd, (struct sockaddr *)&ss, &sslen);
	if (incoming < 0) {
	switch (errno) {
	case EAGAIN:
	case EINTR:
	case ECONNABORTED:
	continue;
	default:
	die("accept returned %s", strerror(errno));
	}
	}
	handle(incoming, (struct sockaddr *)&ss, sslen);
	}
	}
	}
	}

	int main(int argc, char **argv)
	{
	int port = DEFAULT_GIT_PORT;
	int inetd_mode = 0;
	int i;

	for (i = 1; i < argc; i++) {
	char *arg = argv[i];

	if (!strncmp(arg, "--port=", 7)) {
	char *end;
	unsigned long n;
	n = strtoul(arg+7, &end, 0);
	if (arg[7] && !*end) {
	port = n;
	continue;
	}
	}

	if (!strcmp(arg, "--inetd")) {
	inetd_mode = 1;
	continue;
	}

	usage(daemon_usage);
	}

	if (inetd_mode)
	return execute();

	return serve(port);
	}