illumos gate

When using unlinkat() with a directory opened with Linux's O_PATH, it succeeds, otherwise it fails:

        fd = open("/a", O_RDONLY | O_DIRECTORY);
        r = unlinkat(fd, "cccc", 0);
        printf("Ret %d errno %d\n", r, errno);
...
# ./test
Ret -1 errno 22

        fd = open("/a", O_RDONLY | O_DIRECTORY | O_PATH);
        r = unlinkat(fd, "cccc", 0);
        printf("Ret %d errno %d\n", r, errno);
...
# ./test
Ret 0 errno 0

Using AT_FDCWD also works:

        r = unlinkat(AT_FDCWD, "cccc", 0);
        printf("Ret %d errno %d\n", r, errno);
...
# cd /a; ./test
Ret 0 errno 0

In addition to this, Tunlinkat is part of 9P2000.L and is expected to return error numbers consistent with a Linux implementation. The illumos unlinkat(, AT_REMOVEDIR) call returns EEXIST when the directory is not empty, whereas Linux expects the ENOTEMPTY error code in this case.

See also https://github.com/conclusiveeng/lib9p/pull/18

Testing notes:

With the fix in place, each of the tests shown above succeeds. In a Linux guest, the unlinkat call is able to remove a file with AT_FDCWD and with a file descriptor that was opened with, and without O_PATH.

I also verified that attempting to unlink a non-empty directory now returns the linux ENOTEMPTY value (which differs from the illumos one - 39 versus 93).

[root@bhyvetest ~]# mount | grep /a
bob on /a type 9p (rw,relatime,sync,dirsync,uname=root,access=client,trans=virtio)
[root@bhyvetest ~]# cd /a
[root@bhyvetest ~]# mkdir -p b/c
[root@bhyvetest a]# strace -e unlinkat ./test
unlinkat(3, "b", AT_REMOVEDIR)          = -1 ENOTEMPTY (Directory not empty)
Ret -1 errno 39