fs-util: readlinkat() supports an empty string

From readlinkat(2):
Since Linux 2.6.39, pathname can be an empty string, in which case the
call operates on the symbolic link referred to by dirfd (which should
have been obtained using open(2) with the O_PATH and O_NOFOLLOW flags).

1 files changed, 35 insertions, 0 deletions

diff --git a/src/test/test-fs-util.c b/src/test/test-fs-util.c
index 5de1eea0d4..ef335b43ae 100644
--- a/src/test/test-fs-util.c
+++ b/src/test/test-fs-util.c
@@ -758,4 +758,39 @@ static int intro(void) {
         return EXIT_SUCCESS;
 }
 
+TEST(readlinkat_malloc) {
+        _cleanup_(rm_rf_physical_and_freep) char *t = NULL;
+        _cleanup_close_ int tfd = -EBADF, fd = -EBADF;
+        _cleanup_free_ char *p = NULL, *q = NULL;
+        const char *expect = "hgoehogefoobar";
+
+        tfd = mkdtemp_open(NULL, O_PATH, &t);
+        assert_se(tfd >= 0);
+
+        assert_se(symlinkat(expect, tfd, "linkname") >= 0);
+
+        assert_se(readlinkat_malloc(tfd, "linkname", &p) >= 0);
+        assert_se(streq(p, expect));
+        p = mfree(p);
+
+        fd = openat(tfd, "linkname", O_PATH | O_NOFOLLOW | O_CLOEXEC);
+        assert_se(fd >= 0);
+        assert_se(readlinkat_malloc(fd, NULL, &p) >= 0);
+        assert_se(streq(p, expect));
+        p = mfree(p);
+        assert_se(readlinkat_malloc(fd, "", &p) >= 0);
+        assert_se(streq(p, expect));
+        p = mfree(p);
+        fd = safe_close(fd);
+
+        assert_se(q = path_join(t, "linkname"));
+        assert_se(readlinkat_malloc(AT_FDCWD, q, &p) >= 0);
+        assert_se(streq(p, expect));
+        p = mfree(p);
+        assert_se(readlinkat_malloc(INT_MAX, q, &p) >= 0);
+        assert_se(streq(p, expect));
+        p = mfree(p);
+        q = mfree(q);
+}
+
 DEFINE_TEST_MAIN_WITH_INTRO(LOG_INFO, intro);