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From: Peter Lieven <pl@kamp.de>
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Date: Wed, 17 Jul 2013 12:26:12 +0200
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Subject: Re: [Qemu-devel] [PATCH 16/17] block: add default get_block_status
	implementation for protocols
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: kwolf@redhat.com, qemu-devel@nongnu.org, stefanha@redhat.com


Am 16.07.2013 um 09:19 schrieb Paolo Bonzini <pbonzini@redhat.com>:

> Il 16/07/2013 08:47, Peter Lieven ha scritto:
>>>=20
>>> @@ -2977,7 +2977,11 @@ static int64_t coroutine_fn
>>> bdrv_co_get_block_status(BlockDriverState *bs,
>>>        if (!bs->drv->bdrv_co_get_block_status) {
>>>          *pnum =3D nb_sectors;
>>> -        return BDRV_BLOCK_DATA;
>>> +        ret =3D BDRV_BLOCK_DATA;
>>> +        if (bs->drv->protocol_name) {
>>> +            ret |=3D BDRV_BLOCK_OFFSET_VALID | (sector_num *
>>> BDRV_SECTOR_SIZE);
>>> +        }
>>> +        return ret;
>>>      }
>>>        ret =3D bs->drv->bdrv_co_get_block_status(bs, sector_num,
>>> nb_sectors, pnum);
>> I am curious if this is right. Doesn't this mean we say that at =
offset
>> sector_num * BDRV_SECTOR_SIZE are nb_sectors of linear data? This is
>> something we do not know for sure.
>=20
> Only for protocols.  In this case, we do know, or format=3Draw =
wouldn't
> work.  This is not propagated up to the actual BDS for the image, =
except
> for format=3Draw.

Wouldn't it be better to add this general tweak in to =
raw_co_is_allocated
rather than at the block level?

What you write above is true, but you will never know what will happen =
in the
future. For raw this tweak is right, but for anything developed in the =
future
it might not be and in the end nobody remembers to fix it at this =
position.

I was just thinking of the has_zero_init =3D 1 thing. At the time it was =
written
the code was correct and then came more and more extensions like
extends on a block device or iscsi and nobody remembered.

Peter=