Re: [PATCH v5 5/6] liveupdate: Add LIVEUPDATE_SESSION_FREEZE ioctl to freeze sessions early

["Pasha Tatashin" <pasha.tatashin@soleen.com>]

On Wed Nov 11, 2026 at 6:18 AM EST, Mike Rapoport wrote:
> Hi,
>
>> Currently, LUO sessions are frozen automatically only inside the
>> reboot(LINUX_REBOOT_CMD_KEXEC) pathway, where luo_session_serialize()
>> iterates through all outgoing sessions under global write locks and
>> freezes them serially during shutdown. On hosts running multiple
>> workloads that quiesce one by one ahead of kexec, userspace needs an
>> explicit per-session freeze point so each session can capture final file
>> state under its per-session mutex as soon as its workload pauses.
>> 
>> Introduce LIVEUPDATE_SESSION_FREEZE on session FDs to freeze an outgoing
>> session early. The ioctl runs .freeze() across all preserved files in
>> the session and serializes their metadata. Once frozen, no additional
>> files can be added to the session, and subsequent freeze calls return
>> -EBUSY. Freeze is only valid on outgoing sessions and returns -EINVAL on
>> incoming ones.
>> 
>> By default (flags == 0), session lifetime remains bound to the session
>> FD: the session stays frozen while the FD remains open, and closing the
>> session FD before reboot (for example, to abort the session or on
>> process exit/crash) unfreezes it via .unfreeze(), unpreserves its files,
>> and reclaims all resources. During kexec, already-frozen sessions skip
>> the late auto-freeze and are published into the outgoing KHO subtree.
>> 
>> With LIVEUPDATE_SESSION_FREEZE_COMMIT set in
>> struct liveupdate_session_freeze.flags, the frozen session is committed:
>> it and its FLB dependencies are immediately inserted into the outgoing
>> KHO subtree via luo_session_publish_one(), and the session survives
>> close() with full ownership retained by LUO until reboot. Once
>> committed, closing the session FD (or another session failing to freeze
>> during reboot) never unfreezes or unpreserves the session, allowing
>> processes to hand off preserved state and exit prior to kexec.
>> 
>> Update the uAPI and core LUO documentation to describe session freeze
>> and commit semantics.
>
> Please teach your LLM to use shorter paragraphs, focus on why and don't
> list every implementation detail, but only important ones.

The first paragraph explains exactly why; however, I agree that it needs 
to be more concise. I will address your comments in v6. Thanks!

-- 
Pasha