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Re: [Qemu-devel] [PULL 8/9] static checker: e1000-82540em got aliased to

From: Jason Wang
Subject: Re: [Qemu-devel] [PULL 8/9] static checker: e1000-82540em got aliased to e1000
Date: Wed, 6 Apr 2016 09:48:19 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0

On 04/05/2016 09:32 PM, Dr. David Alan Gilbert wrote:
> * Amit Shah (address@hidden) wrote:
>> On (Tue) 23 Feb 2016 [15:02:58], Jason Wang wrote:
>>>>> This means that 2.5 cannot migrate 2.4 virtual machines, right?  Is that
>>>>> something we want to rectify in 2.6 by making e1000-82540em an alias of
>>>>> e1000 (instead of the other way round)?
>>>> You're right; I misread it.  With that commit (8304402033):
>>>> 2.4 with e1000-82540em will not migrate to 2.5 with e1000-82540em.
>>>> This is despite they're aliased (so the cmdline is backward
>>>> compatible), but the migration device name actually changed.
>>>> Of course, 2.5->2.4 will also not work.
>>>> Since 2.4 emits 'e1000-82540em' as the device name in the migration
>>>> stream, and 2.5 emits just 'e1000', we have two different names for
>>>> the same device in two versions.
>>>> To fix this, we'll need a hack on the dest side to allow e1000 and
>>>> e1000-82540em in the migration stream for the device, and this can be
>>>> done for 2.6 and 2.5.stable.
>>>> Jason, can you attempt this?
>>> Sure, but just need to understand the "problem". If I understand this
>>> correctly, the issue only happen for JSON description at the end of
>>> migration stream, and it won't break migration in fact?
>> No, this does break migration.
>> The stream contained 'e1000-82540em' as the section header for the
>> device earlier.  It now only has 'e1000'.  So a newer qemu will only
>> accept 'e1000', but not 'e1000-82540em' (from an older release).
> OK, so do we need to get this fixed for 2.6 - i.e. now.
> Dave

Sorry for the late response.

Have a try with 2.4 -> 2.5 migration and it works. Looking at
save_section_header(), it will save se->idstr which seems always be
"e1000" even if e1000-82540em is used in cli, or is there anything I missed?

>>              Amit
> --
> Dr. David Alan Gilbert / address@hidden / Manchester, UK

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