stat-util: introduce {stat,fd}_verify_linked()

src/basic/stat-util.c

@@ -260,6 +260,26 @@ int path_is_network_fs(const char *path) {
         return is_network_fs(&s);
 }
 
+int stat_verify_linked(const struct stat *st) {
+        assert(st);
+
+        if (st->st_nlink <= 0)
+                return -EIDRM; /* recognizable error. */
+
+        return 0;
+}
+
+int fd_verify_linked(int fd) {
+        struct stat st;
+
+        assert(fd >= 0);
+
+        if (fstat(fd, &st) < 0)
+                return -errno;
+
+        return stat_verify_linked(&st);
+}
+
 int stat_verify_regular(const struct stat *st) {
         assert(st);
 

src/basic/stat-util.h

@@ -72,6 +72,9 @@ int path_is_network_fs(const char *path);
  */
 #define F_TYPE_EQUAL(a, b) (a == (typeof(a)) b)
 
+int stat_verify_linked(const struct stat *st);
+int fd_verify_linked(int fd);
+
 int stat_verify_regular(const struct stat *st);
 int fd_verify_regular(int fd);
 int verify_regular_at(int dir_fd, const char *path, bool follow);

src/test/test-stat-util.c

@@ -195,6 +195,25 @@ TEST(inode_type_from_string) {
                 assert_se(inode_type_from_string(inode_type_to_string(*m)) == *m);
 }
 
+TEST(fd_verify_linked) {
+        _cleanup_(rm_rf_physical_and_freep) char *t = NULL;
+        _cleanup_close_ int tfd = -EBADF, fd = -EBADF;
+        _cleanup_free_ char *p = NULL;
+
+        tfd = mkdtemp_open(NULL, O_PATH, &t);
+        assert_se(tfd >= 0);
+
+        assert_se(p = path_join(t, "hoge"));
+        assert_se(touch(p) >= 0);
+
+        fd = open(p, O_CLOEXEC | O_PATH);
+        assert_se(fd >= 0);
+
+        assert_se(fd_verify_linked(fd) >= 0);
+        assert_se(unlinkat(tfd, "hoge", 0) >= 0);
+        assert_se(fd_verify_linked(fd) == -EIDRM);
+}
+
 static int intro(void) {
         log_show_color(true);
         return EXIT_SUCCESS;