Use initalization instead of explicit zeroing

Before, we would initialize many fields twice: first
by filling the structure with zeros, and then a second
time with the real values. We can let the compiler do
the job for us, avoiding one copy.

A downside of this patch is that text gets slightly
bigger. This is because all zero() calls are effectively
inlined:

$ size build/.libs/systemd
         text    data     bss     dec     hex filename
before 897737  107300    2560 1007597   f5fed build/.libs/systemd
after  897873  107300    2560 1007733   f6075 build/.libs/systemd

… actually less than 1‰.

A few asserts that the parameter is not null had to be removed. I
don't think this changes much, because first, it is quite unlikely
for the assert to fail, and second, an immediate SEGV is almost as
good as an assert.

src/journal/journald-server.c

@@ -719,7 +719,7 @@ void server_driver_message(Server *s, sd_id128_t message_id, const char *format,
         struct iovec iovec[N_IOVEC_META_FIELDS + 4];
         int n = 0;
         va_list ap;
-        struct ucred ucred;
+        struct ucred ucred = {};
 
         assert(s);
         assert(format);
@@ -740,7 +740,6 @@ void server_driver_message(Server *s, sd_id128_t message_id, const char *format,
                 IOVEC_SET_STRING(iovec[n++], mid);
         }
 
-        zero(ucred);
         ucred.pid = getpid();
         ucred.uid = getuid();
         ucred.gid = getgid();
@@ -1356,17 +1355,16 @@ static int server_open_sync_timer(Server *s) {
 int server_schedule_sync(Server *s) {
         int r;
 
-        struct itimerspec sync_timer_enable;
-
         assert(s);
 
         if (s->sync_scheduled)
                 return 0;
 
         if (s->sync_interval_usec) {
-                zero(sync_timer_enable);
-                sync_timer_enable.it_value.tv_sec = s->sync_interval_usec / USEC_PER_SEC;
-                sync_timer_enable.it_value.tv_nsec = s->sync_interval_usec % MSEC_PER_SEC;
+                struct itimerspec sync_timer_enable = {
+                        .it_value.tv_sec = s->sync_interval_usec / USEC_PER_SEC,
+                        .it_value.tv_nsec = s->sync_interval_usec % MSEC_PER_SEC,
+                };
 
                 r = timerfd_settime(s->sync_timer_fd, 0, &sync_timer_enable, NULL);
                 if (r < 0)

src/journal/journald-stream.c

@@ -412,13 +412,16 @@ fail:
 }
 
 int server_open_stdout_socket(Server *s) {
-        union sockaddr_union sa;
         int r;
         struct epoll_event ev;
 
         assert(s);
 
         if (s->stdout_fd < 0) {
+                union sockaddr_union sa = {
+                        .un.sun_family = AF_UNIX,
+                        .un.sun_path = "/run/systemd/journal/stdout",
+                };
 
                 s->stdout_fd = socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
                 if (s->stdout_fd < 0) {
@@ -426,10 +429,6 @@ int server_open_stdout_socket(Server *s) {
                         return -errno;
                 }
 
-                zero(sa);
-                sa.un.sun_family = AF_UNIX;
-                strncpy(sa.un.sun_path, "/run/systemd/journal/stdout", sizeof(sa.un.sun_path));
-
                 unlink(sa.un.sun_path);
 
                 r = bind(s->stdout_fd, &sa.sa, offsetof(union sockaddr_union, un.sun_path) + strlen(sa.un.sun_path));

src/journal/journald-syslog.c

@@ -34,28 +34,28 @@
 #define WARN_FORWARD_SYSLOG_MISSED_USEC (30 * USEC_PER_SEC)
 
 static void forward_syslog_iovec(Server *s, const struct iovec *iovec, unsigned n_iovec, struct ucred *ucred, struct timeval *tv) {
-        struct msghdr msghdr;
+
+        union sockaddr_union sa = {
+                .un.sun_family = AF_UNIX,
+                .un.sun_path = "/run/systemd/journal/syslog",
+        };
+        struct msghdr msghdr = {
+                .msg_iov = (struct iovec *) iovec,
+                .msg_iovlen = n_iovec,
+                .msg_name = &sa,
+                .msg_namelen = offsetof(union sockaddr_union, un.sun_path)
+                               + sizeof("/run/systemd/journal/syslog") - 1,
+        };
         struct cmsghdr *cmsg;
         union {
                 struct cmsghdr cmsghdr;
                 uint8_t buf[CMSG_SPACE(sizeof(struct ucred))];
         } control;
-        union sockaddr_union sa;
 
         assert(s);
         assert(iovec);
         assert(n_iovec > 0);
 
-        zero(msghdr);
-        msghdr.msg_iov = (struct iovec*) iovec;
-        msghdr.msg_iovlen = n_iovec;
-
-        zero(sa);
-        sa.un.sun_family = AF_UNIX;
-        strncpy(sa.un.sun_path, "/run/systemd/journal/syslog", sizeof(sa.un.sun_path));
-        msghdr.msg_name = &sa;
-        msghdr.msg_namelen = offsetof(union sockaddr_union, un.sun_path) + strlen(sa.un.sun_path);
-
         if (ucred) {
                 zero(control);
                 msghdr.msg_control = &control;
@@ -412,13 +412,16 @@ void server_process_syslog_message(
 }
 
 int server_open_syslog_socket(Server *s) {
-        union sockaddr_union sa;
         int one, r;
         struct epoll_event ev;
 
         assert(s);
 
         if (s->syslog_fd < 0) {
+                union sockaddr_union sa = {
+                        .un.sun_family = AF_UNIX,
+                        .un.sun_path = "/dev/log",
+                };
 
                 s->syslog_fd = socket(AF_UNIX, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
                 if (s->syslog_fd < 0) {
@@ -426,10 +429,6 @@ int server_open_syslog_socket(Server *s) {
                         return -errno;
                 }
 
-                zero(sa);
-                sa.un.sun_family = AF_UNIX;
-                strncpy(sa.un.sun_path, "/dev/log", sizeof(sa.un.sun_path));
-
                 unlink(sa.un.sun_path);
 
                 r = bind(s->syslog_fd, &sa.sa, offsetof(union sockaddr_union, un.sun_path) + strlen(sa.un.sun_path));