linux-kernel - Re: [PATCH v1 17/32] liveupdate: luo

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Message-ID: <d6e44430-ec9c-4d77-a00b-15e97ab9beab@infradead.org>
Date: Wed, 25 Jun 2025 17:29:15 -0700
From: Randy Dunlap <rdunlap@...radead.org>
To: Pasha Tatashin <pasha.tatashin@...een.com>, pratyush@...nel.org,
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Subject: Re: [PATCH v1 17/32] liveupdate: luo_sysfs: add sysfs state
 monitoring

Hi,


On 6/25/25 4:18 PM, Pasha Tatashin wrote:
> diff --git a/Documentation/ABI/testing/sysfs-kernel-liveupdate b/Documentation/ABI/testing/sysfs-kernel-liveupdate
> new file mode 100644
> index 000000000000..4cd4a4fe2f93
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-kernel-liveupdate
> @@ -0,0 +1,51 @@
> +What:		/sys/kernel/liveupdate/
> +Date:		May 2025
> +KernelVersion:	6.16.0
> +Contact:	pasha.tatashin@...een.com
> +Description:	Directory containing interfaces to query the live
> +		update orchestrator. Live update is the ability to reboot the
> +		host kernel (e.g., via kexec, without a full power cycle) while
> +		keeping specifically designated devices operational ("alive")
> +		across the transition. After the new kernel boots, these devices
> +		can be re-attached to their original workloads (e.g., virtual
> +		machines) with their state preserved. This is particularly
> +		useful, for example, for quick hypervisor updates without
> +		terminating running virtual machines.
> +
> +
> +What:		/sys/kernel/liveupdate/state
> +Date:		May 2025
> +KernelVersion:	6.16.0
> +Contact:	pasha.tatashin@...een.com
> +Description:	Read-only file that displays the current state of the live
> +		update orchestrator as a string. Possible values are:
> +
> +		"normal":	No live update operation is in progress. This is
> +				the default operational state.

Just an opinion, but the ':'s after each possible value aren't needed
and just add noise.

You could just drop the ':'s -- or you could make a table here, like
Documentation/ABI/testing/sysfs-hypervisor-xen does, by adding

                ===========     ================================================


> +		"prepared":	The live update preparation phase has completed
> +				successfully (e.g., triggered via the
> +				/dev/liveupdate event). Kernel subsystems have
> +				been notified via the %LIVEUPDATE_PREPARE
> +				event/callback and should have initiated state
> +				saving. User workloads (e.g., VMs) are generally
> +				still running, but some operations (like device
> +				unbinding or new DMA mappings) might be
> +				restricted. The system is ready for the reboot
> +				trigger.
> +
> +		"frozen":	The final reboot notification has been sent
> +				(e.g., triggered via the 'reboot()' syscall),
> +				corresponding to the %LIVEUPDATE_REBOOT kernel
> +				event. Subsystems have had their final chance to
> +				save state. User workloads must be suspended.
> +				The system is about to execute the reboot into
> +				the new kernel (imminent kexec). This state
> +				corresponds to the "blackout window".
> +
> +		"updated":	The system has successfully rebooted into the
> +				new kernel via live update. Restoration of
> +				preserved resources can now occur (typically via
> +				ioctl commands). The system is awaiting the
> +				final 'finish' signal after user space completes
> +				restoration tasks.

and

                ===========     ================================================

Or just disagree or ignore. :)

-- 
~Randy