Re: [Xen-devel] [PATCH for-4.6 v2 2/6] docs/libxl: Re-specify XENSTORE_DATA as EMULATOR_XENSTORE_DATA

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 04/08/15 10:40, Ian Campbell wrote:
> On Mon, 2015-08-03 at 16:56 +0100, Andrew Cooper wrote:
>> The legacy "toolstack" record as implemented in libxl turns out not to
>> be 32/64bit safe.  As migration v2 has not shipped yet, take this
>> opportunity to adjust the specification and fix the incompatibility.
>>
>> Libxl shall loose all knowledge of the old "toolstack" blob and use this
>> EMULATOR_XENSTORE_DATA record instead.  Compatibility shall be handled
>> by the legacy conversion script.
>>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>> ---
>> CC: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
>> CC: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
>> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
>>
>> v2:
>>  * More adjustments to the libxl spec.
>>  * Make the emulator id/index table common and move it up beside the
>>    record type/length table.
>>  * Be more specific about the format and encoding of the xenstore
>>    key/value data.
>>  * Add a note about the unspecified nature of the emulator context blob.
>> ---
>>  docs/specs/libxl-migration-stream.pandoc   |   83 ++++++++++++++++++++--
>> ------
>>  tools/libxl/libxl_sr_stream_format.h       |   11 ++--
>>  tools/python/scripts/convert-legacy-stream |    2 +-
>>  tools/python/xen/migration/legacy.py       |   40 +++++++++++++-
>>  tools/python/xen/migration/libxl.py        |   71 +++++++++++++++++-----
>> --
>>  tools/python/xen/migration/tests.py        |    2 +-
>>  6 files changed, 155 insertions(+), 54 deletions(-)
>>
>> diff --git a/docs/specs/libxl-migration-stream.pandoc b/docs/specs/libxl
>> -migration-stream.pandoc
>> index cdec168..85adbf0 100644
>> --- a/docs/specs/libxl-migration-stream.pandoc
>> +++ b/docs/specs/libxl-migration-stream.pandoc
>> @@ -90,8 +90,8 @@ i386, x86_64, or arm host.
>>  \clearpage
>>  
>>  
>> -Records
>> -=======
>> +Record Overview
>> +===============
>>  
>>  A record has a record header, type specific data and a trailing footer. 
>>  If
>>  `length` is not a multiple of 8, the body is padded with zeroes to align 
>> the
>> @@ -113,7 +113,7 @@ type         0x00000000: END
>>  
>>               0x00000001: LIBXC_CONTEXT
>>  
>> -             0x00000002: XENSTORE_DATA
>> +             0x00000002: EMULATOR_XENSTORE_DATA
>>  
>>               0x00000003: EMULATOR_CONTEXT
>>  
>> @@ -135,6 +135,39 @@ padding      0 to 7 octets of zeros to pad the whole 
>> record to a multiple
>>  
>>  \clearpage
>>  
>> +Emulator Records
>> +----------------
>> +
>> +Several records are specifically for emulators, and have a common sub 
>> header.
> It would be useful to mention in the specific records which have this
> header that they do, I think.

Each record containing this sub header identify all the fields,
including id and index.  I can list them, although they are currently
all the EMULATOR_* records.

>
>> +
>> +     0     1     2     3     4     5     6     7 octet
>> +    +------------------------+------------------------+
>> +    | emulator_id            | index                  |
>> +    +------------------------+------------------------+
>> +    | record specific data                            |
>> +    ...
>> +    +-------------------------------------------------+
>> +
>> +--------------------------------------------------------------------
>> +Field            Description
>> +------------     ---------------------------------------------------
>> +emulator_id      0x00000000: Unknown (In the case of a legacy stream)
>> +
>> +                 0x00000001: Qemu Traditional
>> +
>> +                 0x00000002: Qemu Upstream
>> +
>> +                 0x00000003 - 0xFFFFFFFF: Reserved for future emulators.
>> +
>> +index            Index of this emulator for the domain, if multiple
>> +                 emulators are in use.
> This is old wording, but what value does this take if no emulators are in
> use? If the answer is "undefined" then I suppose there is a field somewhere
> else which indicates the number of emulators?

If no emulators are in use, the record is not sent in the first place.

~Andrew

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