path_test: fix cap_rights_init usage

Capability rights passed to cap_rights_* are not simple bitmaks and
cannot be ORed together in general (although it will work for certain
subsets of rights).

PR: 277057
Fixes: e5e1d9c7b781 ("path_test: Add a test case for...")
Sponsored by: The FreeBSD Foundation

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix

path_test: Add a test case for openat(O_EMPTY_PATH) in capability mode

MFC after: 1 week

path_test: Verify that operations on unlinked files work

MFC after: 1 week
Sponsored by: The FreeBSD Foundation

path_test: Correct the kevent test

Perhaps surprisingly, and contrary to the expectations of
path_test:path_event, NOTE_LINK events are not raised when a file is
unlinked. Prior to commit bf13db086b84, the test happened to work
because unlinking the file would cause the vnode to be recycled, and
EVFILT_VNODE knotes deliver an event with EV_EOF set when the vnode is
doomed. Since the test did not verify the note type, the test
succeeded. After commit bf13db086b84, the vnode is not recycled after
being unlinked and so the test hangs.

Fix the test by waiting for NOTE_DELETE instead, and check that we got
the note that we expected.

Reported by: Jenkins
MFC after: 3 days
Sponsored by: The FreeBSD Foundation

Have path_test ask the kernel for the page size

It may be dynamic so we can't rely on PAGE_SIZE being present or
correct.

Sponsored by: The FreeBSD Foundation

vfs: Permit unix sockets to be opened with O_PATH

As with FIFOs, a path descriptor for a unix socket cannot be used with
kevent().

In principle connectat(2) and bindat(2) could be modified to support an
AT_EMPTY_PATH-like mode which operates on the socket referenced by an
O_PATH fd referencing a unix socket. That would eliminate the path
length limit imposed by sockaddr_un.

Update O_PATH tests.

Reviewed by: kib
MFC after: 1 month
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D31970

path_test: Fix test sorting

MFC after: 1 week
Sponsored by: The FreeBSD Foundation

path_test: Fix the unix socket test

The intent was to specify O_PATH to open(2).

MFC after: 1 week
Sponsored by: The FreeBSD Foundation

Add test for fstatat(pipefd, AT_EMPTY_PATH)

Sponsored by: The FreeBSD Foundation
MFC after: 1 week

path_test: Add a few new test cases

MFC after: 1 week
Sponsored by: The FreeBSD Foundation

Add some regression tests for O_PATH and AT_EMPTY_PATH

Reviewed by: kib
MFC after: 2 weeks
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D29719