tree-wide: add ERRNO_IS_XATTR_ABSENT() helper

We check the same list of error codes on various xattr operations, and
we should on some more. Add a common helper for this purpose.

src/basic/errno-util.h

@@ -153,3 +153,10 @@ static inline bool ERRNO_IS_DEVICE_ABSENT(int r) {
                       ENXIO,
                       ENOENT);
 }
+
+/* Quite often we want to handle cases where the backing FS doesn't support extended attributes at all and
+ * where it simply doesn't have the requested xattr the same way */
+static inline bool ERRNO_IS_XATTR_ABSENT(int r) {
+        return abs(r) == ENODATA ||
+                ERRNO_IS_NOT_SUPPORTED(r);
+}

src/basic/os-util.c

@@ -126,7 +126,7 @@ int open_extension_release(const char *root, const char *extension, char **ret_p
                                 /* No xattr or cannot parse it? Then skip this. */
                                 _cleanup_free_ char *extension_release_xattr = NULL;
                                 k = fgetxattr_malloc(extension_release_fd, "user.extension-release.strict", &extension_release_xattr);
-                                if (k < 0 && !ERRNO_IS_NOT_SUPPORTED(k) && k != -ENODATA)
+                                if (k < 0 && !ERRNO_IS_XATTR_ABSENT(k))
                                         log_debug_errno(k,
                                                         "%s/%s: Failed to read 'user.extension-release.strict' extended attribute from file: %m",
                                                         extension_release_dir_path, de->d_name);