fcntl update following up with F_GETPATH but with FreeBSD's F_KINFO f…

[devnexen]

…lag support instead

[asomers]

I was able to reproduce the test failure when I set TMPDIR to UFS, but not ZFS or TMPFS. I believe the CI environment uses UFS. Then I found this gem on the mailing list:

When open(2) creates a new file, the vnode name is not entered into
the name cache.  I believe this is done to smoother the case like
untarring large set of files, which would replace existing cached
entries with probably not too useful new entries.

F_KINFO uses name cache to reconstruct the last element of the path,
on most real file systems like UFS.  If this last element is not cached,
F_KINFO is unable to return the path.

And indeed, if I reopen the tempfile by its path, then the test passes on UFS. Like this:

    let tmp = NamedTempFile::new().unwrap();
    let tmp2 = File::open(tmp.path()).unwrap();
    let fd = tmp2.as_raw_fd();
    let mut path = PathBuf::new();
    let res = fcntl(fd, FcntlArg::F_KINFO(&mut path)).expect("get path failed");

https://lists.freebsd.org/archives/freebsd-hackers/2022-May/001108.html

[devnexen]

I was able to reproduce the test failure when I set TMPDIR to UFS, but not ZFS or TMPFS. I believe the CI environment uses UFS. Then I found this gem on the mailing list:

When open(2) creates a new file, the vnode name is not entered into
the name cache.  I believe this is done to smoother the case like
untarring large set of files, which would replace existing cached
entries with probably not too useful new entries.

F_KINFO uses name cache to reconstruct the last element of the path,
on most real file systems like UFS.  If this last element is not cached,
F_KINFO is unable to return the path.

And indeed, if I reopen the tempfile by its path, then the test passes on UFS. Like this:

    let tmp = NamedTempFile::new().unwrap();
    let tmp2 = File::open(tmp.path()).unwrap();
    let fd = tmp2.as_raw_fd();
    let mut path = PathBuf::new();
    let res = fcntl(fd, FcntlArg::F_KINFO(&mut path)).expect("get path failed");

https://lists.freebsd.org/archives/freebsd-hackers/2022-May/001108.html

Nice find ! I no longer use UFS since ages I did not think of it.

[asomers]

Could you please add a CHANGELOG entry? And add a comment to the test explaining why it opens the file twice? That part looks very non-obvious.

[SteveLauC]

Thanks!