Documentation/userspace-api/liveupdate.rst
.. SPDX-License-Identifier: GPL-2.0
:Author: Pasha Tatashin [email protected]
.. kernel-doc:: kernel/liveupdate/luo_core.c :doc: LUO ioctl Interface
.. kernel-doc:: include/uapi/linux/liveupdate.h
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.
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>_Live Update Orchestrator </core-api/liveupdate>