| .. 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>` |
