hostname: introduce gethostname_full() and use it in various gethostname() variants

src/shared/hostname-setup.c

@@ -20,12 +20,14 @@
 #include "util.h"
 
 static int sethostname_idempotent_full(const char *s, bool really) {
-        char buf[HOST_NAME_MAX + 1];
+        _cleanup_free_ char *buf = NULL;
+        int r;
 
         assert(s);
 
-        if (gethostname(buf, sizeof(buf)) < 0)
-                return -errno;
+        r = gethostname_full(GET_HOSTNAME_ALLOW_NONE | GET_HOSTNAME_ALLOW_LOCALHOST, &buf);
+        if (r < 0)
+                return r;
 
         if (streq(buf, s))
                 return 0;
@@ -41,26 +43,6 @@ int sethostname_idempotent(const char *s) {
         return sethostname_idempotent_full(s, true);
 }
 
-bool get_hostname_filtered(char ret[static HOST_NAME_MAX + 1]) {
-        char buf[HOST_NAME_MAX + 1];
-
-        /* Returns true if we got a good hostname, false otherwise. */
-
-        if (gethostname(buf, sizeof(buf)) < 0)
-                return false;  /* This can realistically only fail with ENAMETOOLONG.
-                                * Let's treat that case the same as an invalid hostname. */
-
-        if (isempty(buf))
-                return false;
-
-        /* This is the built-in kernel default hostname */
-        if (streq(buf, "(none)"))
-                return false;
-
-        memcpy(ret, buf, sizeof buf);
-        return true;
-}
-
 int shorten_overlong(const char *s, char **ret) {
         char *h, *p;
 
@@ -195,10 +177,14 @@ int hostname_setup(bool really) {
         }
 
         if (!hn) {
+                _cleanup_free_ char *buf = NULL;
+
                 /* Don't override the hostname if it is already set and not explicitly configured */
 
-                char buf[HOST_NAME_MAX + 1] = {};
-                if (get_hostname_filtered(buf)) {
+                r = gethostname_full(GET_HOSTNAME_ALLOW_LOCALHOST, &buf);
+                if (r == -ENOMEM)
+                        return log_oom();
+                if (r >= 0) {
                         log_debug("No hostname configured, leaving existing hostname <%s> in place.", buf);
                         return 0;
                 }