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.

1 files changed, 5 insertions, 8 deletions

diff --git a/src/nspawn/nspawn.c b/src/nspawn/nspawn.c
index 01ef12bf6..b90ccc53e 100644
--- a/src/nspawn/nspawn.c
+++ b/src/nspawn/nspawn.c
@@ -674,8 +674,11 @@ static int setup_kmsg(const char *dest, int kmsg_socket) {
         union {
                 struct cmsghdr cmsghdr;
                 uint8_t buf[CMSG_SPACE(sizeof(int))];
-        } control;
-        struct msghdr mh;
+        } control = {};
+        struct msghdr mh = {
+                .msg_control = &control,
+                .msg_controllen = sizeof(control),
+        };
         struct cmsghdr *cmsg;
 
         assert(dest);
@@ -716,12 +719,6 @@ static int setup_kmsg(const char *dest, int kmsg_socket) {
                 return -errno;
         }
 
-        zero(mh);
-        zero(control);
-
-        mh.msg_control = &control;
-        mh.msg_controllen = sizeof(control);
-
         cmsg = CMSG_FIRSTHDR(&mh);
         cmsg->cmsg_level = SOL_SOCKET;
         cmsg->cmsg_type = SCM_RIGHTS;