Re: [Qemu-devel] [PATCH 05/12] block: add logical block provisioning information to BlockDriverInfo

[Paolo Bonzini]

Il 13/09/2013 12:44, Peter Lieven ha scritto:
> On 13.09.2013 12:34, Paolo Bonzini wrote:
>> Il 13/09/2013 12:25, Peter Lieven ha scritto:
>>> +    /* maximum number of sectors that can be discarded at once */
>>> +    int max_discard;
>>> +    /* maximum number of sectors that can zeroized at once */
>>> +    int max_write_zeroes;
>> These should not be needed outside the driver.
>>
>> If you want to make them private between block.c and block/iscsi.c, you
>> can add them to BlockDriverState.
> The question is, if the discard_zeroes or discard_write_zeroes is needed
> outside the driver as well?
> 
> I can put the max_* information in the block driver state. I also thought
> to add alignment and granularity information even if they are currently
> not yet used.

Yeah, in fact bdrv_write_zeroes and bdrv_discard can be taught to split
requests according to these parameters instead of introducing a new
function bdrv_zeroize.  You don't need bdrv_zeroize I think; you can
simply use bdrv_write_zeroes.  This is why I don't like this information
in BlockDriverInfo.

On the contrary, discard_write_zeroes is useful to "generic" clients,
and your qemu-img patch shows why.

Discard_zeroes is somewhere in the middle.  You only use it in
bdrv_get_block_status, but it is not something that should be hidden to
users of the high-level block.c API.  So it is fine to leave it in
BlockDriverInfo.

Paolo