Re: [PATCH v3 02/24] PCI: Add API to track PCI devices preserved across Live Update

["Yanjun.Zhu" <yanjun.zhu@linux.dev>]

On 4/6/26 9:06 AM, David Matlack wrote:
> On Sun, Apr 5, 2026 at 9:56 AM Zhu Yanjun <yanjun.zhu@linux.dev> wrote:
>> 在 2026/4/3 14:58, David Matlack 写道:
>>> On Thu, Apr 2, 2026 at 2:29 PM Yanjun.Zhu <yanjun.zhu@linux.dev> wrote:
>>>> On 3/23/26 4:57 PM, David Matlack wrote:
>>>>> +config PCI_LIVEUPDATE
>>>>> +     bool "PCI Live Update Support (EXPERIMENTAL)"
>>>>> +     depends on PCI && LIVEUPDATE
>>>>> +     help
>>>>> +       Support for preserving PCI devices across a Live Update. This option
>>>>> +       should only be enabled by developers working on implementing this
>>>>> +       support. Once enough support as landed in the kernel, this option
>>>>> +       will no longer be marked EXPERIMENTAL.
>>>>> +
>>>>> +       If unsure, say N.
>>>> Currently, it only supports 'n' or 'y'. Is it possible to add 'm'
>>>> (modular support)?
>>>>
>>>> This would allow the feature to be built as a kernel module. For
>>>> development
>>>>
>>>> purposes, modularization means we only need to recompile a single module
>>>>
>>>> for testing, rather than rebuilding the entire kernel. Compiling a
>>>> module should
>>>>
>>>> be significantly faster than a full kernel build.
>>> I don't think it is possible for CONFIG_PCI_LIVEUPDATE to support 'm'.
>>> pci_setup_device() (which is under CONFIG_PCI) needs to call
>>> pci_liveupdate_setup_device(), and CONFIG_PCI cannot be built as a
>>> module. This call is necessary so the PCI core knows whether a device
>>> being enumerated was preserved across a previous Live Update.
>> After the following changes, the liveupdate.ko can be generated
>> successfully.
> Sure but you've broken the feature. Now devices can be probed before
> liveupdate.ko is loaded and the PCI core will have an incorrect view

 From this perspective, I think it makes sense.

Zhu Yanjun

> of which devices were preserved by the previous kernel.