Merge tag 'driver-core-7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/driver-core/driver-coregrafted

Pull driver core fixes from Danilo Krummrich:

 - Fix kernfs listxattr() not returning security xattr names (e.g.
   SELinux labels) when the kernfs node has no allocated kernfs_iattrs

 - Fix silent truncation of IRQ vector indices in the Rust PCI
   abstractions

 - Don't select OF from DRIVER_PE_KUNIT_TEST; skip the test when OF is
   disabled instead of silently enabling extra kernel functionality

 - Russ Weight is retiring from kernel development; update the Firmware
   Loader sysfs contact to the driver-core mailing list, add a CREDITS
   entry for Firmware Upload, and update MAINTAINERS accordingly

* tag 'driver-core-7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/driver-core/driver-core:
  MAINTAINERS: Remove Russ Weight from Firmware Loader
  CREDITS: Add CREDITS entry for Firmware Upload
  firmware_loader: Change contact for sysfs nodes
  rust: pci: reject IRQ vector indices that do not fit in u32
  kernfs: preserve security xattrs without allocating iattrs
  drivers: base: test: DRIVER_PE_KUNIT_TEST should not select OF

1 files changed, 51 insertions, 0 deletions

diff --git a/Documentation/userspace-api/liveupdate.rst b/Documentation/userspace-api/liveupdate.rst
new file mode 100644
index 000000000..cdd74627a
--- /dev/null
+++ b/Documentation/userspace-api/liveupdate.rst
@@ -0,0 +1,51 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+================
+Live Update uAPI
+================
+:Author: Pasha Tatashin <pasha.tatashin@soleen.com>
+
+ioctl interface
+===============
+.. kernel-doc:: kernel/liveupdate/luo_core.c
+   :doc: LUO ioctl Interface
+
+ioctl uAPI
+===========
+.. kernel-doc:: include/uapi/linux/liveupdate.h
+
+Note on Compatibility
+=====================
+
+Note that the Live Update feature is still under development and subject to
+change, so compatibility is not guaranteed when kexec rebooting between
+different kernel versions. This is expected to change and stabilize in a future
+version.
+
+Userspace Integration
+=====================
+
+systemd (since version v261) uses LUO to preserve its per-service file
+descriptor store across a kexec-based live update. Services opt in by setting
+``FileDescriptorStoreMax=`` and ``FileDescriptorStorePreserve=`` in their unit,
+and push file descriptors with a name into the store via
+``sd_pid_notify_with_fds(... "FDSTORE=1\nFDNAME=foo")``.
+
+Services may also create their own LUO sessions (via ``/dev/liveupdate``) and
+push the resulting session fds into their file descriptor store like any other
+fd. systemd detects such session fds and handles them accordingly, and
+hands the re-retrieved session fd back to the service after kexec, using the
+existing file descriptor store service interface.
+
+For details, see:
+
+- `File Descriptor Store <https://systemd.io/FILE_DESCRIPTOR_STORE/>`_
+- `systemd.service(5) FileDescriptorStorePreserve=
+  <https://www.freedesktop.org/software/systemd/man/latest/systemd.service.html#FileDescriptorStorePreserve=>`_
+- `sd_pid_notify_with_fds(3)
+  <https://www.freedesktop.org/software/systemd/man/latest/sd_pid_notify_with_fds.html>`_
+
+See Also
+========
+
+- :doc:`Live Update Orchestrator </core-api/liveupdate>`