Re: [PATCH v3 03/11] block: Let bdrv_co_is_zero_fast consolidate adjacent extents

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Thu, Apr 24, 2025 at 07:52:03PM -0500, Eric Blake wrote:
> Some BDS drivers have a cap on how much block status they can supply
> in one query (for example, NBD talking to an older server cannot
> inspect more than 4G per query; and qcow2 tends to cap its answers
> rather than cross a cluster boundary of an L1 table).  Although the
> existing callers of bdrv_co_is_zero_fast are not passing in that large
> of a 'bytes' parameter, an upcoming caller wants to query the entire
> image at once, and will thus benefit from being able to treat adjacent
> zero regions in a coalesced manner, rather than claiming the region is
> non-zero merely because pnum was truncated and didn't match the
> incoming bytes.
> 
> While refactoring this into a loop, note that there is no need to
> assign pnum prior to calling bdrv_co_common_block_status_above() (it
> is guaranteed to be assigned deeper in the callstack).
> 
> Signed-off-by: Eric Blake <eblake@redhat.com>
> 
> ---
> 
> v3: also tweak function comment
> ---
>  block/io.c | 29 ++++++++++++++++-------------
>  1 file changed, 16 insertions(+), 13 deletions(-)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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