[PATCH v3 3/3] landlock: Document LANDLOCK_RESTRICT_SELF_TSYNC

["Günther Noack" <gnoack@google.com>]

Add documentation for LANDLOCK_RESTRICT_SELF_TSYNC.  It does not need to go
into the main example, but it has a section in the ABI compatibility notes.
In the HTML rendering, the main reference is the system call documentation,
which is included from the landlock.h header file.

Cc: Andrew G. Morgan <morgan@kernel.org>
Cc: John Johansen <john.johansen@canonical.com>
Cc: Mickaël Salaün <mic@digikod.net>
Cc: Paul Moore <paul@paul-moore.com>
Cc: linux-security-module@vger.kernel.org
Signed-off-by: Günther Noack <gnoack@google.com>
---
 Documentation/userspace-api/landlock.rst | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/Documentation/userspace-api/landlock.rst b/Documentation/userspace-api/landlock.rst
index 1d0c2c15c22e..f1251da9877c 100644
--- a/Documentation/userspace-api/landlock.rst
+++ b/Documentation/userspace-api/landlock.rst
@@ -604,6 +604,14 @@ Landlock audit events with the ``LANDLOCK_RESTRICT_SELF_LOG_SAME_EXEC_OFF``,
 sys_landlock_restrict_self().  See Documentation/admin-guide/LSM/landlock.rst
 for more details on audit.
 
+Thread synchronization (ABI < 8)
+--------------------------------
+
+Starting with the Landlock ABI version 8, it is now possible to
+enforce Landlock rulesets across all threads of the calling process
+using the ``LANDLOCK_RESTRICT_SELF_TSYNC`` flag passed to
+sys_landlock_restrict_self().
+
 .. _kernel_support:
 
 Kernel support
-- 
2.52.0.177.g9f829587af-goog