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Re: [PATCH] livepatch: do not use .livepatch.funcs section to store internal state
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 16 Nov 2023 16:11:56 +0100
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- Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Thu, 16 Nov 2023 15:12:47 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 16.11.2023 15:48, Roger Pau Monné wrote:
> On Thu, Nov 16, 2023 at 03:05:20PM +0100, Jan Beulich wrote:
>> On 16.11.2023 14:54, Roger Pau Monné wrote:
>>> On Thu, Nov 16, 2023 at 01:39:27PM +0100, Jan Beulich wrote:
>>>> On 16.11.2023 12:58, Roger Pau Monne wrote:
>>>>> --- a/xen/include/public/sysctl.h
>>>>> +++ b/xen/include/public/sysctl.h
>>>>> @@ -991,10 +991,7 @@ struct livepatch_func {
>>>>> uint32_t new_size;
>>>>> uint32_t old_size;
>>>>> uint8_t version; /* MUST be LIVEPATCH_PAYLOAD_VERSION. */
>>>>> - uint8_t opaque[LIVEPATCH_OPAQUE_SIZE];
>>>>> - uint8_t applied;
>>>>> - uint8_t patch_offset;
>>>>> - uint8_t _pad[6];
>>>>> + uint8_t _pad[39];
>>>>
>>>> Should this be LIVEPATCH_OPAQUE_SIZE+8 and ...
>>>
>>> Hm, I'm not sure that's any clearer. In fact I think
>>> LIVEPATCH_OPAQUE_SIZE shouldn't have leaked into sysctl.h in the first
>>> place.
>>>
>>> If we later want to add more fields and bump the version, isn't it
>>> easier to have the padding size clearly specified as a number?
>>
>> If new fields (beyond the present padding size) would need adding,
>> that would constitute an incompatible change anyway.
>
> Not if we bump the version field I think?
>
> As the version is a strict match, bumping the version allows for a
> completely new layout to be implemented past the 'version' field.
Of course.
Jan
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