Re: [Xen-devel] [PATCH v2] xen: fix qdisk BLKIF_OP_DISCARD for 32/64 word size mix

[Juergen Gross <jgross@xxxxxxxx>]

On 17/06/16 11:37, Paul Durrant wrote:
>> -----Original Message-----
>> From: Xen-devel [mailto:xen-devel-bounces@xxxxxxxxxxxxx] On Behalf Of Jan
>> Beulich
>> Sent: 17 June 2016 10:26
>> To: Juergen Gross
>> Cc: Anthony Perard; xen-devel; sstabellini@xxxxxxxxxx; qemu-
>> devel@xxxxxxxxxx; kraxel@xxxxxxxxxx
>> Subject: Re: [Xen-devel] [PATCH v2] xen: fix qdisk BLKIF_OP_DISCARD for
>> 32/64 word size mix
>>
>>>>> On 17.06.16 at 11:14, <JGross@xxxxxxxx> wrote:
>>> In case the word size of the domU and qemu running the qdisk backend
>>> differ BLKIF_OP_DISCARD will not work reliably, as the request
>>> structure in the ring have different layouts for different word size.
>>>
>>> Correct this by copying the request structure in case of different
>>> word size element by element in the BLKIF_OP_DISCARD case, too.
>>>
>>> The easiest way to achieve this is to resync hw/block/xen_blkif.h with
>>> its original source from the Linux kernel.
>>>
>>> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
>>> ---
>>> V2: resync with Linux kernel version of hw/block/xen_blkif.h as
>>>     suggested by Paul Durrant
>>
>> Oh, I didn't realize he suggested syncing with the Linux variant.
>> Why not with the canonical one? I have to admit that I particularly
>> dislike Linux'es strange union-izng, mainly because of it requiring
>> this myriad of __attribute__((__packed__)).
>>
> 
> Yes, it's truly grotesque and such things should be blown away with extreme 
> prejudice.

Sorry, I'm confused now.

Do you still mandate for the resync or not?

Resyncing with elimination of all the __packed__ stuff seems not to be
a proper alternative as this would require a major rework. So either I
do a resync and keep this stuff or I don't resync at all.


Juergen


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