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| author | Luca Boccassi <luca.boccassi@gmail.com> | 2026-05-19 18:28:39 +0300 |
|---|---|---|
| committer | Mike Rapoport (Microsoft) <rppt@kernel.org> | 2026-06-01 09:19:38 +0300 |
| commit | 608d1642f20077abff382f04bcd74a4a6cec3018 (patch) | |
| tree | e8b60a20663d182ae0b1b85e79fdecb22e8b8e5c | |
| parent | 0e39380a7316122e1b00012b3f3cd3e318b3e7d3 (diff) | |
| download | linux-608d1642f20077abff382f04bcd74a4a6cec3018.tar.xz | |
liveupdate: document systemd support
systemd v261 will add native support for LUO via the file descriptor
store mechanism. Add a brief paragraph in the LUO userspace documentation
page to inform users.
Signed-off-by: Luca Boccassi <luca.boccassi@gmail.com>
Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Acked-by: Pratyush Yadav <pratyush@kernel.org>
Link: https://patch.msgid.link/20260519152957.548119-1-luca.boccassi@gmail.com
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
| -rw-r--r-- | Documentation/userspace-api/liveupdate.rst | 23 |
1 files changed, 23 insertions, 0 deletions
diff --git a/Documentation/userspace-api/liveupdate.rst b/Documentation/userspace-api/liveupdate.rst index 41c0473e4f16..f6efc32fb40b 100644 --- a/Documentation/userspace-api/liveupdate.rst +++ b/Documentation/userspace-api/liveupdate.rst @@ -14,6 +14,29 @@ ioctl uAPI =========== .. kernel-doc:: include/uapi/linux/liveupdate.h +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 ======== |