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Date: Tue, 04 Sep 2012 09:38:50 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 4/6] libqblock internal used functions
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To: Wenchao Xia <xiawenc@linux.vnet.ibm.com>
Cc: kwolf@redhat.com, stefanha@gmail.com, aliguori@us.ibm.com, Eric Blake <eblake@redhat.com>, qemu-devel@nongnu.org

Il 04/09/2012 09:15, Wenchao Xia ha scritto:
>>>>> +/* this file contains helper function used internally. */
>>>>> +#define SECTOR_SIZE (512)
>>> Hard-coding this feels wrong, in this day and age of disks with 4096
>>> sectors.  Why isn't this a per-image property?
>>
>> In this day and age of disks with 4096 sectors, Linux does not provide a
>> way to query the required alignment for O_DIRECT...
>>
>> Paolo
>>
> in block.h:
> #define BDRV_SECTOR_BITS   9
> #define BDRV_SECTOR_SIZE   (1ULL << BDRV_SECTOR_BITS)
> #define BDRV_SECTOR_MASK   ~(BDRV_SECTOR_SIZE - 1)
>   it seems block size is always 512 in qemu block layer, so I can
> ignore the 4096 case, do you think so?

Yes.  It is not well supported yet by QEMU, either.

Paolo