Re: [Qemu-devel] [PATCH 7/8] iscsi: assert that sectors are aligned to LUN blocksize

[Peter Lieven]

Am 24.06.2013 18:27, schrieb Paolo Bonzini:
> 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.
It would be the easiest. Maybe Ronnie can point out what the hack
with the acb->buffer_offset in aio_read was meant for. All other
functions have the requirement to be properly aligned regarding
to the xfersize. I am also not sure if the e.g. reading of 512 byte
at sector 0 from a 4K block device does still work with the
iovector patches we added earlier.

Peter
>
> Paolo