add ENABLE_FEATURE_SYSTEMD and use it in syslogd

Signed-off-by: Davide Cavalca <davide@geexbox.org>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

include/libbb.h

@@ -1217,6 +1217,12 @@ extern void selinux_preserve_fcontext(int fdesc) FAST_FUNC;
 #endif
 extern void selinux_or_die(void) FAST_FUNC;
 
+
+/* systemd support */
+#define SD_LISTEN_FDS_START 3
+int sd_listen_fds(void);
+
+
 /* setup_environment:
  * if chdir pw->pw_dir: ok: else if to_tmp == 1: goto /tmp else: goto / or die
  * if clear_env = 1: cd(pw->pw_dir), clear environment, then set

libbb/systemd_support.c

@@ -0,0 +1,62 @@
+/*
+ * Copyright (C) 2011 Davide Cavalca <davide@geexbox.org>
+ *
+ * Based on http://cgit.freedesktop.org/systemd/tree/src/sd-daemon.c
+ * Copyright 2010 Lennart Poettering
+ *
+ * Permission is hereby granted, free of charge, to any person
+ * obtaining a copy of this software and associated documentation files
+ * (the "Software"), to deal in the Software without restriction,
+ * including without limitation the rights to use, copy, modify, merge,
+ * publish, distribute, sublicense, and/or sell copies of the Software,
+ * and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+#include "libbb.h"
+
+//config:config FEATURE_SYSTEMD
+//config:	bool "Enable systemd support"
+//config:	default y
+//config:	help
+//config:	  If you plan to use busybox daemons on a system where daemons
+//config:	  are controlled by systemd, enable this option.
+//config:	  If you don't use systemd, it is still safe to enable it,
+//config:	  but yhe downside is increased code size.
+
+//kbuild:lib-$(CONFIG_FEATURE_SYSTEMD) += systemd_support.o
+
+int sd_listen_fds(void)
+{
+	const char *e;
+	int n;
+	int fd;
+
+	e = getenv("LISTEN_PID");
+	if (!e)
+		return 0;
+	n = xatoi_positive(e);
+	/* Is this for us? */
+	if (getpid() != (pid_t) n)
+		return 0;
+
+	e = getenv("LISTEN_FDS");
+	if (!e)
+		return 0;
+	n = xatoi_positive(e);
+	for (fd = SD_LISTEN_FDS_START; fd < SD_LISTEN_FDS_START + n; fd++)
+		close_on_exec_on(fd);
+
+	return n;
+}

sysklogd/syslogd.c

@@ -512,6 +512,11 @@ static NOINLINE int create_socket(void)
 	int sock_fd;
 	char *dev_log_name;
 
+#if ENABLE_FEATURE_SYSTEMD
+	if (sd_listen_fds() == 1)
+		return SD_LISTEN_FDS_START;
+#endif
+
 	memset(&sunx, 0, sizeof(sunx));
 	sunx.sun_family = AF_UNIX;