Re: [Qemu-devel] [PULL 33/42] block: return BDRV_BLOCK_ZERO past end of backing file

[Peter Lieven <lieven-lists@dlhnet.de>]

On 13.09.2013 17:20, Kevin Wolf wrote:
> Am 13.09.2013 um 10:25 hat Paolo Bonzini geschrieben:
>> Il 13/09/2013 09:33, Peter Lieven ha scritto:
>>> On 06.09.2013 17:39, Stefan Hajnoczi wrote:
>>>> From: Paolo Bonzini <pbonzini@redhat.com>
>>>>
>>>> If the sectors are unallocated and we are past the end of the
>>>> backing file, they will read as zero.
>>>>
>>>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>>>> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
>>>> ---
>>>>    block.c | 12 ++++++++++--
>>>>    1 file changed, 10 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/block.c b/block.c
>>>> index aa9ec83..82bbd6c 100644
>>>> --- a/block.c
>>>> +++ b/block.c
>>>> @@ -3102,8 +3102,16 @@ static int64_t coroutine_fn
>>>> bdrv_co_get_block_status(BlockDriverState *bs,
>>>>            return ret;
>>>>        }
>>>>    -    if (!(ret & BDRV_BLOCK_DATA) && bdrv_has_zero_init(bs)) {
>>>> -        ret |= BDRV_BLOCK_ZERO;
>>>> +    if (!(ret & BDRV_BLOCK_DATA)) {
>>>> +        if (bdrv_has_zero_init(bs)) {
>>> this should be bdi->discard_zeroes. bdrv_has_zero_init() does only give
>>> a valid result
>>> right after bdrv_create(). i currently working on extending bdi. I can
>>> send a patch for this
>>> if you agree.
>> Yes, please.  Right now there is no bdi->discard_zeroes.
> If we do this, it needs some function that behaves similar to
> bdrv_has_zero_init(); in particular that it returns 0 if there is a
> backing file.
I will add bdrv_has_discard_zeroes. Would it be ok if it calls out to
bdrv_get_info to get the discard_zeroes information?

Peter