On 05-19 16:28, [email protected] wrote: > From: Luca Boccassi <[email protected]> > > 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 <[email protected]> > --- > NOTE: the external links will mention LUO after the next release is > published, which should happen within ~4 weeks > > Documentation/userspace-api/liveupdate.rst | 23 ++++++++++++++++++++++ > 1 file changed, 23 insertions(+) > > 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>`_ > +
Reviewed-by: Pasha Tatashin <[email protected]> > See Also > ======== > > -- > 2.47.3 >
