Minor optimization, drop expensive memset() ops

No need to zero out whole buffer for strlcat(), or other string check
ops.  Also drop a few completely useless memset() calls.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/api.c

@@ -110,7 +110,7 @@ static int missing(char *job, char *id)
 
 static int do_query(char *buf, size_t len)
 {
-	memset(query_buf, 0, sizeof(query_buf));
+	query_buf[0] = 0;
 	if (svc_parse_jobstr(buf, len, NULL, missing)) {
 		memcpy(buf, query_buf, len);
 		return 1;

src/conf.c

@@ -357,7 +357,7 @@ char *lim2str(struct rlimit *rlim)
 	char tmp[25];
 	static char buf[42];
 
-	memset(buf, 0, sizeof(buf));
+	buf[0] = 0;
 	if (RLIM_INFINITY == rlim->rlim_cur)
 		snprintf(tmp, sizeof(tmp), "unlimited, ");
 	else
@@ -661,7 +661,7 @@ static int parse_conf(char *file, int is_rcsd)
 	/* Prepare default limits and group for each service in /etc/finit.d/ */
 	if (is_rcsd) {
 		memcpy(rlimit, global_rlimit, sizeof(rlimit));
-		memset(cgroup_current, 0, sizeof(cgroup_current));
+		cgroup_current[0] = 0;
 	}
 
 	_d("*** Parsing %s", file);

src/helpers.c

@@ -260,7 +260,7 @@ void print_banner(const char *heading)
 	if (progress_style == PROGRESS_SILENT)
 		return;
 
-	memset(buf, 0, sizeof(buf));
+	buf[0] = 0;
 	strlcat(buf, "\r\e[2K", sizeof(buf));
 
 	if (progress_style == PROGRESS_CLASSIC) {
@@ -339,7 +339,7 @@ void printv(const char *fmt, va_list ap)
 
 	delline();
 
-	memset(buf, 0, sizeof(buf));
+	buf[0] = 0;
 	len = print_timestamp(buf, sizeof(buf));
 	vsnprintf(&buf[len], sizeof(buf) - len, fmt, ap);
 

src/initctl.c

@@ -120,7 +120,6 @@ static int runlevel_get(int *prevlevel)
 	int result;
 	struct init_request rq;
 
-	memset(&rq, 0, sizeof(rq));
 	rq.cmd = INIT_CMD_GET_RUNLEVEL;
 	rq.magic = INIT_MAGIC;
 
@@ -359,7 +358,7 @@ static char *svc_cond(svc_t *svc, char *buf, size_t len)
 {
 	char *cond, *conds;
 
-	memset(buf, 0, len);
+	buf[0] = 0;
 
 	if (!svc->cond[0])
 		return buf;
@@ -485,10 +484,7 @@ int utmp_show(char *file)
 	while ((ut = getutent())) {
 		char addr[64];
 
-		memset(id, 0, sizeof(id));
 		strlcpy(id, ut->ut_id, sizeof(id));
-
-		memset(user, 0, sizeof(user));
 		strlcpy(user, ut->ut_user, sizeof(user));
 
 		sec = ut->ut_tv.tv_sec;