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| author | Mark Brown <broonie@kernel.org> | 2026-05-29 22:46:36 +0100 |
|---|---|---|
| committer | Mark Brown <broonie@kernel.org> | 2026-05-29 22:46:37 +0100 |
| commit | b3897f4d6b7c3d92f8bb098038327766da8ba06d (patch) | |
| tree | 095730507e9a2c7f22b291c91b7d1aa873967f5b /Documentation | |
| parent | e2bd485974b30605aaa2fd4b8b6551d9a1846a62 (diff) | |
| parent | 5428435567cbe06c19914592fc22ca23c9ca1de5 (diff) | |
| download | linux-next-history-b3897f4d6b7c3d92f8bb098038327766da8ba06d.tar.gz | |
Merge branch 'next' of https://git.kernel.org/pub/scm/linux/kernel/git/liveupdate/linux.git
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/userspace-api/liveupdate.rst | 31 |
1 files changed, 31 insertions, 0 deletions
diff --git a/Documentation/userspace-api/liveupdate.rst b/Documentation/userspace-api/liveupdate.rst index 41c0473e4f160..cdd74627ab75b 100644 --- a/Documentation/userspace-api/liveupdate.rst +++ b/Documentation/userspace-api/liveupdate.rst @@ -14,6 +14,37 @@ 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 ======== |