Support systemd socket activation.

Makefile.am

@@ -14,6 +14,7 @@ aux_sources = \
 	pq.c \
 	primes.c \
 	prot.c \
+	sd-daemon.c \
 	tube.c \
 	util.c
 beanstalkd_SOURCES = beanstalkd.c $(aux_sources)
@@ -45,6 +46,7 @@ EXTRA_DIST = cut.c $(tests) $(scripts) $(readme) cut.h sh-tests check.sh check-o
 	primes.h \
 	prot.h \
 	stat.h \
+	sd-daemon.h \
 	tube.h \
 	util.h
 

beanstalkd.c

@@ -35,6 +35,7 @@
 #include <limits.h>
 
 #include "net.h"
+#include "sd-daemon.h"
 #include "util.h"
 #include "prot.h"
 #include "binlog.h"
@@ -202,6 +203,14 @@ require_arg(char *opt, char *arg)
     return arg;
 }
 
+static void
+warn_systemd_ignored_option(char *opt, char *arg)
+{
+    if (sd_listen_fds(0) > 0) {
+        warnx("inherited listen fd; ignoring option: %s %s", opt, arg);
+    }
+}
+
 static void
 opts(int argc, char **argv)
 {
@@ -216,9 +225,11 @@ opts(int argc, char **argv)
                 break;
             case 'p':
                 port = require_arg("-p", argv[++i]);
+                warn_systemd_ignored_option("-p", argv[i]);
                 break;
             case 'l':
                 host_addr = require_arg("-l", argv[++i]);
+                warn_systemd_ignored_option("-l", argv[i]);
                 break;
             case 'z':
                 job_data_size_limit = parse_size_t(require_arg("-z",

net.c

@@ -21,6 +21,7 @@
 #include <errno.h>
 
 #include "net.h"
+#include "sd-daemon.h"
 #include "util.h"
 
 static int listen_socket = -1;
@@ -36,6 +37,33 @@ make_server_socket(char *host, char *port)
     struct linger linger = {0, 0};
     struct addrinfo *airoot, *ai, hints;
 
+    /* See if we got a listen fd from systemd. If so, all socket options etc
+     * are already set, so we check that the fd is a TCP listen socket and
+     * return. */
+    r = sd_listen_fds(1);
+    if (r < 0) {
+        return twarn("sd_listen_fds"), -1;
+    }
+    if (r > 0) {
+        if (r > 1) {
+            twarnx("inherited more than one listen socket;"
+                   " ignoring all but the first");
+            r = 1;
+        }
+        fd = SD_LISTEN_FDS_START;
+        r = sd_is_socket_inet(fd, 0, SOCK_STREAM, 1, 0);
+        if (r < 0) {
+            errno = -r;
+            twarn("sd_is_socket_inet");
+            return -1;
+        }
+        if (!r) {
+            twarnx("inherited fd is not a TCP listen socket");
+            return -1;
+        }
+        return listen_socket = fd;
+    }
+
     memset(&hints, 0, sizeof(hints));
     hints.ai_family = PF_UNSPEC;
     hints.ai_socktype = SOCK_STREAM;