git-daemon: rewrite kindergarden, new option --max-connections

Get rid of the fixed array of children and make max-connections
dynamic and configurable.
Fix the killing code to actually kill the newest connections from
duplicate IP-addresses.
Avoid forking if too busy already.

Signed-off-by: Stephen R. van den Berg <srb@cuci.nl>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/Documentation/git-daemon.txt b/Documentation/git-daemon.txt
index 4ba4b75c1126d87c48935e7697e05f0d5210ad2d..b08a08cd95b6da192a008c58d7973769dfe3fc8c 100644 (file)
--- a/Documentation/git-daemon.txt
+++ b/Documentation/git-daemon.txt
@@ -9,8 +9,9 @@ SYNOPSIS
 --------
 [verse]
 'git daemon' [--verbose] [--syslog] [--export-all]
-            [--timeout=n] [--init-timeout=n] [--strict-paths]
-            [--base-path=path] [--user-path | --user-path=path]
+            [--timeout=n] [--init-timeout=n] [--max-connections=n]
+            [--strict-paths] [--base-path=path] [--base-path-relaxed]
+            [--user-path | --user-path=path]
             [--interpolated-path=pathtemplate]
             [--reuseaddr] [--detach] [--pid-file=file]
             [--enable=service] [--disable=service]
@@ -99,6 +100,10 @@ OPTIONS
        it takes for the server to process the sub-request and time spent
        waiting for next client's request.
 
+--max-connections::
+       Maximum number of concurrent clients, defaults to 32.  Set it to
+       zero for no limit.
+
 --syslog::
        Log to syslog instead of stderr. Note that this option does not imply
        --verbose, thus by default only error conditions will be logged.

diff --git a/daemon.c b/daemon.c
index 3abacfd9d923c9b1fd4f2022b247c399c2ad1ee9..79f0388204848f1e1085c48be8e6a86bb14cef68 100644 (file)
--- a/daemon.c
+++ b/daemon.c
@@ -19,8 +19,8 @@ static int reuseaddr;
 
 static const char daemon_usage[] =
 "git daemon [--verbose] [--syslog] [--export-all]\n"
-"           [--timeout=n] [--init-timeout=n] [--strict-paths]\n"
-"           [--base-path=path] [--base-path-relaxed]\n"
+"           [--timeout=n] [--init-timeout=n] [--max-connections=n]\n"
+"           [--strict-paths] [--base-path=path] [--base-path-relaxed]\n"
 "           [--user-path | --user-path=path]\n"
 "           [--interpolated-path=path]\n"
 "           [--reuseaddr] [--detach] [--pid-file=file]\n"
@@ -584,40 +584,35 @@ static int execute(struct sockaddr *addr)
        return -1;
 }
 
+static int max_connections = 32;
 
-/*
- * 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;
-static pid_t dead_child[MAX_CHILDREN];
-
-/* These are updated by the main loop */
-static unsigned int children_spawned;
-static unsigned int children_deleted;
+static unsigned int live_children;
 
 static struct child {
+       struct child *next;
        pid_t pid;
-       int addrlen;
        struct sockaddr_storage address;
-} live_child[MAX_CHILDREN];
+} *firstborn;
 
-static void add_child(int idx, pid_t pid, struct sockaddr *addr, int addrlen)
+static void add_child(pid_t pid, struct sockaddr *addr, int addrlen)
 {
-       live_child[idx].pid = pid;
-       live_child[idx].addrlen = addrlen;
-       memcpy(&live_child[idx].address, addr, addrlen);
+       struct child *newborn;
+       newborn = xcalloc(1, sizeof *newborn);
+       if (newborn) {
+               struct child **cradle;
+
+               live_children++;
+               newborn->pid = pid;
+               memcpy(&newborn->address, addr, addrlen);
+               for (cradle = &firstborn; *cradle; cradle = &(*cradle)->next)
+                       if (!memcmp(&(*cradle)->address, &newborn->address,
+                                  sizeof newborn->address))
+                               break;
+               newborn->next = *cradle;
+               *cradle = newborn;
+       }
+       else
+               logerror("Out of memory spawning new child");
 }
 
 /*
@@ -626,142 +621,78 @@ static void add_child(int idx, pid_t pid, struct sockaddr *addr, int addrlen)
  * 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)
+static void remove_child(pid_t pid)
 {
-       struct child n;
+       struct child **cradle, *blanket;
 
-       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;
-       }
+       for (cradle = &firstborn; (blanket = *cradle); cradle = &blanket->next)
+               if (blanket->pid == pid) {
+                       *cradle = blanket->next;
+                       live_children--;
+                       free(blanket);
+                       break;
+               }
 }
 
 /*
  * 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.
+ * We kill the newest connection from a duplicate IP.
  */
-static void kill_some_children(int signo, unsigned start, unsigned stop)
+static void kill_some_child(void)
 {
-       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_dead_children(void)
-{
-       unsigned spawned, reaped, deleted;
-
-       for (;;) {
-               int status;
-               pid_t pid = waitpid(-1, &status, WNOHANG);
-
-               if (pid > 0) {
-                       unsigned reaped = children_reaped;
-                       if (!WIFEXITED(status) || WEXITSTATUS(status) > 0)
-                               pid = -pid;
-                       dead_child[reaped % MAX_CHILDREN] = pid;
-                       children_reaped = reaped + 1;
-                       continue;
-               }
-               break;
-       }
-
-       spawned = children_spawned;
-       reaped = children_reaped;
-       deleted = children_deleted;
-
-       while (deleted < reaped) {
-               pid_t pid = dead_child[deleted % MAX_CHILDREN];
-               const char *dead = pid < 0 ? " (with error)" : "";
+       const struct child *blanket;
 
-               if (pid < 0)
-                       pid = -pid;
+       if ((blanket = firstborn)) {
+               const struct child *next;
 
-               /* XXX: Custom logging, since we don't wanna getpid() */
-               if (verbose) {
-                       if (log_syslog)
-                               syslog(LOG_INFO, "[%d] Disconnected%s",
-                                               pid, dead);
-                       else
-                               fprintf(stderr, "[%d] Disconnected%s\n",
-                                               pid, dead);
-               }
-               remove_child(pid, deleted, spawned);
-               deleted++;
+               for (; (next = blanket->next); blanket = next)
+                       if (!memcmp(&blanket->address, &next->address,
+                                  sizeof next->address)) {
+                               kill(blanket->pid, SIGTERM);
+                               break;
+                       }
        }
-       children_deleted = deleted;
 }
 
-static void check_max_connections(void)
+static void check_dead_children(void)
 {
-       for (;;) {
-               int active;
-               unsigned spawned, deleted;
-
-               check_dead_children();
-
-               spawned = children_spawned;
-               deleted = children_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;
+       int status;
+       pid_t pid;
 
-               /* If the SIGTERM thing isn't helping use SIGKILL */
-               kill_some_children(SIGKILL, deleted, spawned);
-               sleep(1);
+       while ((pid = waitpid(-1, &status, WNOHANG))>0) {
+               const char *dead = "";
+               remove_child(pid);
+               if (!WIFEXITED(status) || WEXITSTATUS(status) > 0)
+                       dead = " (with error)";
+               loginfo("[%d] Disconnected%s", (int)pid, dead);
        }
 }
 
 static void handle(int incoming, struct sockaddr *addr, int addrlen)
 {
-       pid_t pid = fork();
+       pid_t pid;
 
-       if (pid) {
-               unsigned idx;
+       if (max_connections && live_children >= max_connections) {
+               kill_some_child();
+               sleep(1);                        /* give it some time to die */
+               check_dead_children();
+               if (live_children >= max_connections) {
+                       close(incoming);
+                       logerror("Too many children, dropping connection");
+                       return;
+               }
+       }
 
+       if ((pid = fork())) {
                close(incoming);
-               if (pid < 0)
+               if (pid < 0) {
+                       logerror("Couldn't fork %s", strerror(errno));
                        return;
+               }
 
-               idx = children_spawned % MAX_CHILDREN;
-               children_spawned++;
-               add_child(idx, pid, addr, addrlen);
-
-               check_max_connections();
+               add_child(pid, addr, addrlen);
                return;
        }
 
@@ -1077,6 +1008,12 @@ int main(int argc, char **argv)
                        init_timeout = atoi(arg+15);
                        continue;
                }
+               if (!prefixcmp(arg, "--max-connections=")) {
+                       max_connections = atoi(arg+18);
+                       if (max_connections < 0)
+                               max_connections = 0;            /* unlimited */
+                       continue;
+               }
                if (!strcmp(arg, "--strict-paths")) {
                        strict_paths = 1;
                        continue;