Re: [PATCH v5 01/22] liveupdate: luo_core: luo_ioctl: Live Update Orchestrator
From: Mike Rapoport <rppt@kernel.org>
Date: 2025-11-13 13:38:10
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linux-doc, linux-fsdevel, linux-mm, lkml
On Fri, Nov 07, 2025 at 04:02:59PM -0500, Pasha Tatashin wrote:
Introduce LUO, a mechanism intended to facilitate kernel updates while keeping designated devices operational across the transition (e.g., via kexec). The primary use case is updating hypervisors with minimal disruption to running virtual machines. For userspace side of hypervisor update we have copyless migration. LUO is for updating the kernel. This initial patch lays the groundwork for the LUO subsystem. Further functionality, including the implementation of state transition logic, integration with KHO, and hooks for subsystems and file descriptors, will be added in subsequent patches. Create a character device at /dev/liveupdate. A new uAPI header, <uapi/linux/liveupdate.h>, will define the necessary structures. The magic number for IOCTL is registered in Documentation/userspace-api/ioctl/ioctl-number.rst. Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com> ---
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@@ -0,0 +1,46 @@ +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */ + +/* + * Userspace interface for /dev/liveupdate + * Live Update Orchestrator + * + * Copyright (c) 2025, Google LLC. + * Pasha Tatashin <pasha.tatashin@soleen.com> + */ + +#ifndef _UAPI_LIVEUPDATE_H +#define _UAPI_LIVEUPDATE_H + +#include <linux/ioctl.h> +#include <linux/types.h> + +/** + * DOC: General ioctl format + *
It seems it's not linked from Documentation/.../liveupdate.rst
+ * The ioctl interface follows a general format to allow for extensibility. Each + * ioctl is passed in a structure pointer as the argument providing the size of + * the structure in the first u32. The kernel checks that any structure space + * beyond what it understands is 0. This allows userspace to use the backward + * compatible portion while consistently using the newer, larger, structures. + * + * ioctls use a standard meaning for common errnos: + * + * - ENOTTY: The IOCTL number itself is not supported at all + * - E2BIG: The IOCTL number is supported, but the provided structure has + * non-zero in a part the kernel does not understand. + * - EOPNOTSUPP: The IOCTL number is supported, and the structure is + * understood, however a known field has a value the kernel does not + * understand or support. + * - EINVAL: Everything about the IOCTL was understood, but a field is not + * correct. + * - ENOENT: A provided token does not exist. + * - ENOMEM: Out of memory. + * - EOVERFLOW: Mathematics overflowed. + * + * As well as additional errnos, within specific ioctls.
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--- a/kernel/liveupdate/Kconfig +++ b/kernel/liveupdate/Kconfig@@ -1,7 +1,34 @@ # SPDX-License-Identifier: GPL-2.0-only +# +# Copyright (c) 2025, Google LLC. +# Pasha Tatashin <pasha.tatashin@soleen.com> +# +# Live Update Orchestrator +# menu "Live Update and Kexec HandOver" +config LIVEUPDATE + bool "Live Update Orchestrator" + depends on KEXEC_HANDOVER + help + Enable the Live Update Orchestrator. Live Update is a mechanism, + typically based on kexec, that allows the kernel to be updated + while keeping selected devices operational across the transition. + These devices are intended to be reclaimed by the new kernel and + re-attached to their original workload without requiring a device + reset. + + Ability to handover a device from current to the next kernel depends + on specific support within device drivers and related kernel + subsystems. + + This feature primarily targets virtual machine hosts to quickly update + the kernel hypervisor with minimal disruption to the running virtual + machines. + + If unsure, say N. +
Not a big deal, but since LIVEUPDATE depends on KEXEC_HANDOVER, shouldn't it go after KEXEC_HANDOVER?
config KEXEC_HANDOVER bool "kexec handover" depends on ARCH_SUPPORTS_KEXEC_HANDOVER && ARCH_SUPPORTS_KEXEC_FILE
-- Sincerely yours, Mike.