util: unify reading of /proc/cmdline

Instead of individually checking for containers in each user do this
once in a new call proc_cmdline() that read the file only if we are not
in a container.

src/core/condition.c

@@ -86,14 +86,11 @@ static bool test_kernel_command_line(const char *parameter) {
 
         assert(parameter);
 
-        if (detect_container(NULL) > 0)
-                return false;
-
-        r = read_one_line_file("/proc/cmdline", &line);
-        if (r < 0) {
+        r = proc_cmdline(&line);
+        if (r < 0)
                 log_warning("Failed to read /proc/cmdline, ignoring: %s", strerror(-r));
+        if (r <= 0)
                 return false;
-        }
 
         equal = !!strchr(parameter, '=');
         pl = strlen(parameter);

src/core/main.c

@@ -691,19 +691,14 @@ static int parse_config_file(void) {
 static int parse_proc_cmdline(void) {
         _cleanup_free_ char *line = NULL;
         char *w, *state;
-        int r;
         size_t l;
+        int r;
 
-        /* Don't read /proc/cmdline if we are in a container, since
-         * that is only relevant for the host system */
-        if (detect_container(NULL) > 0)
-                return 0;
-
-        r = read_one_line_file("/proc/cmdline", &line);
-        if (r < 0) {
+        r = proc_cmdline(&line);
+        if (r < 0)
                 log_warning("Failed to read /proc/cmdline, ignoring: %s", strerror(-r));
+        if (r <= 0)
                 return 0;
-        }
 
         FOREACH_WORD_QUOTED(w, l, line, state) {
                 _cleanup_free_ char *word;
@@ -979,11 +974,13 @@ static int parse_argv(int argc, char *argv[]) {
                  * relevant for the container, hence we rely on argv[]
                  * instead. */
 
-                for (a = argv; a < argv + argc; a++)
-                        if ((r = parse_proc_cmdline_word(*a)) < 0) {
+                for (a = argv; a < argv + argc; a++) {
+                        r = parse_proc_cmdline_word(*a);
+                        if (r < 0) {
                                 log_error("Failed on cmdline argument %s: %s", *a, strerror(-r));
                                 return r;
                         }
+                }
         }
 
         return 0;

src/core/shutdown.c

@@ -140,8 +140,8 @@ int main(int argc, char *argv[]) {
         int cmd, r;
 
         /* suppress shutdown status output if 'quiet' is used  */
-        r = read_one_line_file("/proc/cmdline", &line);
-        if (r >= 0) {
+        r = proc_cmdline(&line);
+        if (r > 0) {
                 char *w, *state;
                 size_t l;