Re: [Qemu-devel] [PATCH 16/17] block: add default get_block_status implementation for protocols

[Paolo Bonzini]

Il 16/07/2013 09:54, Peter Lieven ha scritto:
> On 16.07.2013 09:19, Paolo Bonzini wrote:
>> Il 16/07/2013 08:47, Peter Lieven ha scritto:
>>>> @@ -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 = nb_sectors;
>>>> -        return BDRV_BLOCK_DATA;
>>>> +        ret = BDRV_BLOCK_DATA;
>>>> +        if (bs->drv->protocol_name) {
>>>> +            ret |= BDRV_BLOCK_OFFSET_VALID | (sector_num *
>>>> BDRV_SECTOR_SIZE);
>>>> +        }
>>>> +        return ret;
>>>>        }
>>>>          ret = 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.
>> Only for protocols.  In this case, we do know, or format=raw wouldn't
>> work.  This is not propagated up to the actual BDS for the image, except
>> for format=raw.
> If bs->drv->protocol_name is only != NULL if format=raw, I am
> fine with this.

No, bs->drv->protocol_name is only != NULL if it is a protocol (like
file or iscsi) rather than a format (like raw or qcow2). :)

But the user will never call bdrv_co_get_block_status on a protocol
(bs->file, roughly), only on a format (bs); and this information is only
passed from bs->file to bs for format=raw.  Other formats compute the
offsets themselves.

Paolo