Re: [Xen-devel] [PATCH] tools/many: Fix Generation ID restore interface.

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 26/11/13 10:45, Ian Campbell wrote:
> On Tue, 2013-11-26 at 10:41 +0000, Andrew Cooper wrote:
>> On 26/11/13 10:11, Ian Campbell wrote:
>>> On Mon, 2013-11-25 at 20:40 +0000, Andrew Cooper wrote:
>>>> The original Generation ID code was submitted before the specification had
>>>> been finalised, and changed completely between the final draft and formal
>>>> release.
>>>>
>>>> Most notably, the size of the Generation ID has doubled to 128 bits, and
>>>> changing it now involves writing a new cryptographically random number in 
>>>> the
>>>> appropriate location, rather than simply incrementing it.
>>>>
>>>> The xc_domain_save() side of the code is fine, but the xc_domain_restore()
>>>> needs substantial changes to be usable.
>>>>
>>>> This patch replaces the old xc_domain_restore() parameters with a new 
>>>> optional
>>>> restore_callback.  If the callback is provided, and an appropriate hunk is
>>>> found in the migration stream, the appropriate piece of guest memory is 
>>>> mapped
>>>> and provided to the callback.
>>>>
>>>> This patch also fixes all the in-tree callers of xc_domain_restore().  All
>>>> callers had the functionality disabled, and never exposed in a public way.
>>>>
>>>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>>>> CC: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
>>>> CC: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
>>>> CC: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
>>>>
>>>> ---
>>>>
>>>> George:
>>>>
>>>>   Despite this being a feature, I am requesting a freeze exemption.  It is
>>>>   functionality which was not used (or indeed useful) before, and remains 
>>>> that
>>>>   way as far as in-tree consumers are concerned.
>>> If it is  both wrong and neither used nor useful why aren't we ripping
>>> it out?
>> The implementation in the tree currently is neither useful nor used.  It
>> is hardwired to disabled for each intree caller, which is why this
>> change wont affect any current functionality in tree.
> That doesn't answer my question.

Well I am ripping out the old interface.  It is at the same time as
providing a new sane interface to be used.

Just because there are no intree users doesn't mean there are no users. 
Part of moving Xapi to libxl will involve plumbing all this stuff into
libxl.

~Andrew

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