[GIT PULL] test/hardlink: add test for `AT_EMPTY_PATH` flag

[charliemirabile]

This PR adds a test for the issue documented in #995. The new test will only run as root. Since the issue requires an upstream change, the test is not passing currently, but as a sanity check, the following patch can be applied to replace the call to uring's version of linkat with an equivalent call to regular linkat and the test will pass.

---
 test/hardlink.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/hardlink.c b/test/hardlink.c
index cf170d0..2d328d1 100644
--- a/test/hardlink.c
+++ b/test/hardlink.c
@@ -95,7 +95,7 @@ int main(int argc, char *argv[])
    if(geteuid()) {
        fprintf(stdout, "not root, skipping AT_EMPTY_PATH test\n");
    } else {
-       ret = do_linkat(&ring, fd, "", emptyname, AT_EMPTY_PATH);
+       ret = linkat(fd, "", AT_FDCWD, emptyname, AT_EMPTY_PATH);
        if (ret < 0) {
            if (ret == -EBADF || ret == -EINVAL) {
                fprintf(stdout, "linkat not supported, skipping\n");
-- 
2.41.0

---

git request-pull output:

The following changes since commit 9dc95a03e4a764e42b9e62990bb00feb9307ba63:

  test/no-mmap-inval: 0 return is fine too (2023-11-07 08:05:52 -0700)

are available in the Git repository at:

  https://github.com/charliemirabile/liburing.git at_empty_path

for you to fetch changes up to f0fe0515ca3c162fac545528ffddc45398d7d181:

  test/hardlink: Add test for `AT_EMPTY_PATH` flag (2023-11-20 05:38:35 -0500)

----------------------------------------------------------------
Charles Mirabile (4):
      test/hardlink: Cleanup error handling
      test/hardlink: add parameter for old's dirfd to `do_linkat`
      test/hardlink: introduce `fd` variable to hold the file open file descriptor
      test/hardlink: Add test for `AT_EMPTY_PATH` flag

 test/hardlink.c | 88 ++++++++++++++++++++++++++++++++++++++++++++++++----------------------------------------
 1 file changed, 48 insertions(+), 40 deletions(-)

---

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---

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[charliemirabile]

Kernel patch here: https://lore.kernel.org/io-uring/20231120105545.1209530-1-cmirabil@redhat.com/