util-lib: beef path_is_os_tree() up a bit

Let's use chase_symlinks() when looking for /etc/os-release and
/usr/lib/os-release as these files might be symlinks (and actually are IRL on
some distros).

diff --git a/src/basic/stat-util.c b/src/basic/stat-util.c
index 81c13ec59436c64c0a0c345361785a0144fffea2..2a6e89b75e9c02a04689733c604e7a02f0a25701 100644 (file)
--- a/src/basic/stat-util.c
+++ b/src/basic/stat-util.c
@@ -150,22 +150,29 @@ int path_is_read_only_fs(const char *path) {
 
 #if 0 /// UNNEEDED by elogind
 int path_is_os_tree(const char *path) {
-        char *p;
         int r;
 
         assert(path);
 
-        /* We use /usr/lib/os-release as flag file if something is an OS */
-        p = strjoina(path, "/usr/lib/os-release");
-        r = access(p, F_OK);
-        if (r >= 0)
-                return 1;
+        /* Does the path exist at all? If not, generate an error immediately. This is useful so that a missing root dir
+         * always results in -ENOENT, and we can properly distuingish the case where the whole root doesn't exist from
+         * the case where just the os-release file is missing. */
+        if (laccess(path, F_OK) < 0)
+                return -errno;
 
-        /* Also check for the old location in /etc, just in case. */
-        p = strjoina(path, "/etc/os-release");
-        r = access(p, F_OK);
+        /* We use /usr/lib/os-release as flag file if something is an OS */
+        r = chase_symlinks("/usr/lib/os-release", path, CHASE_PREFIX_ROOT, NULL);
+        if (r == -ENOENT) {
+
+                /* Also check for the old location in /etc, just in case. */
+                r = chase_symlinks("/etc/os-release", path, CHASE_PREFIX_ROOT, NULL);
+                if (r == -ENOENT)
+                        return 0; /* We got nothing */
+        }
+        if (r < 0)
+                return r;
 
-        return r >= 0;
+        return 1;
 }
 #endif // 0