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

[Kevin Wolf]

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 <address@hidden>
> >>
> >> 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 <address@hidden>
> >> Signed-off-by: Stefan Hajnoczi <address@hidden>
> >> ---
> >>   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.

Kevin