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Date: Mon, 24 Jun 2013 18:27:28 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 7/8] iscsi: assert that sectors are aligned
	to LUN blocksize
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To: Peter Lieven <pl@kamp.de>
Cc: Kevin Wolf <kwolf@redhat.com>, ronniesahlberg@gmail.com, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>

Il 24/06/2013 18:24, Peter Lieven ha scritto:
>> > So far, 4K blocksize is usable if you also specify the same block size
>> > for the guest device.  I have posted once the patches to do
>> > read-modify-write, but I never really pursued inclusion of those.
>> >
>> > In any case, the right place to fix this is the block layer;
>> > driver-specific hacks are... hacks. :)
> Where do I find the sector size if not in BDRV_SECTOR_SIZE?
> Is there a dynamic field or is the answer qemu only support 512 Byte
> sector size at the moment?

bdrv_read/write and friends are always in 512-byte units.

There is bs->buffer_alignment for the guest sector size, but it is not
set at bdrv_open, only later.  So I think QEMU support for bigger
sectors is too sparse to be useful.

> So you would go for fail to open a device if the LUN blocksize is
> not equal to BDRV_SECTOR_SIZE?

Either that, or fails reads/writes that are not aligned.

Paolo