fs-util: add new CHASE_NOFOLLOW flag to chase_symlinks()

This flag mimics what "O_NOFOLLOW|O_PATH" does for open(2) that is
chase_symlinks() will not resolve the final pathname component if it's a
symlink and instead will return a file descriptor referring to the symlink
itself.

Note: if CHASE_SAFE is also passed, no safety checking is performed on the
transition done if the symlink would have been followed.

1 files changed, 25 insertions, 0 deletions

diff --git a/src/test/test-fs-util.c b/src/test/test-fs-util.c
index fc650b513e..d188c24f7b 100644
--- a/src/test/test-fs-util.c
+++ b/src/test/test-fs-util.c
@@ -22,6 +22,7 @@ static void test_chase_symlinks(void) {
         _cleanup_free_ char *result = NULL;
         char temp[] = "/tmp/test-chase.XXXXXX";
         const char *top, *p, *pslash, *q, *qslash;
+        struct stat st;
         int r, pfd;
 
         assert_se(mkdtemp(temp));
@@ -266,6 +267,30 @@ static void test_chase_symlinks(void) {
                 assert_se(sd_id128_equal(a, b));
         }
 
+        /* Test CHASE_NOFOLLOW */
+
+        p = strjoina(temp, "/target");
+        q = strjoina(temp, "/symlink");
+        assert_se(symlink(p, q) >= 0);
+        pfd = chase_symlinks(q, NULL, CHASE_OPEN|CHASE_NOFOLLOW, &result);
+        assert_se(pfd > 0);
+        assert_se(path_equal(result, q));
+        assert_se(fstat(pfd, &st) >= 0);
+        assert_se(S_ISLNK(st.st_mode));
+        result = mfree(result);
+
+        /* s1 -> s2 -> nonexistent */
+        q = strjoina(temp, "/s1");
+        assert_se(symlink("s2", q) >= 0);
+        p = strjoina(temp, "/s2");
+        assert_se(symlink("nonexistent", p) >= 0);
+        pfd = chase_symlinks(q, NULL, CHASE_OPEN|CHASE_NOFOLLOW, &result);
+        assert_se(pfd > 0);
+        assert_se(path_equal(result, q));
+        assert_se(fstat(pfd, &st) >= 0);
+        assert_se(S_ISLNK(st.st_mode));
+        result = mfree(result);
+
         /* Test CHASE_ONE */
 
         p = strjoina(temp, "/start");