On 09/07/2016 09:15 AM, Jeff Cody wrote:
> On Tue, Sep 06, 2016 at 06:11:19PM +0300, Denis V. Lunev wrote:
>> bdrv_is_allocated_above() returns true in the case if qcow2 even for
>> completely zeroed areas as BDRV_BLOCK_ALLOCATED flag is set in both
>> cases.
> Hi Denis,
>
> Not just qcow2. BDRV_BLOCK_ALLOCATED for a layer means the content of the
> block is defined by that layer (even if that is a zero block, that doesn't
> mean it is unallocated). This applies to all image formats.
>
>> Though we have completely zeroed out the image just above or it was
>> already zeroed.
> This is only true if we are in 'sync = full' mode.
>
>> The patch stops using bdrv_is_allocated_above() wrapper and switches to
>> bdrv_get_block_status_above() to distinguish zeroed areas and areas with
>> data to avoid extra IO operations, which could be VERY slow.
> For 'sync = top', we need to make sure to appropriately allocate the sector,
> even if it is BDRV_BLOCK_ZERO.
>
>> Signed-off-by: Denis V. Lunev <d...@openvz.org>
>> CC: Jeff Cody <jc...@redhat.com>
>> CC: Kevin Wolf <kw...@redhat.com>
>> CC: Max Reitz <mre...@redhat.com>
>> ---
>> block/mirror.c | 13 ++++++++-----
>> 1 file changed, 8 insertions(+), 5 deletions(-)
>>
>> diff --git a/block/mirror.c b/block/mirror.c
>> index e0b3f41..87edbd8 100644
>> --- a/block/mirror.c
>> +++ b/block/mirror.c
>> @@ -552,7 +552,7 @@ static int coroutine_fn mirror_dirty_init(MirrorBlockJob
>> *s)
>> BlockDriverState *base = s->base;
>> BlockDriverState *bs = blk_bs(s->common.blk);
>> BlockDriverState *target_bs = blk_bs(s->target);
>> - int ret, n;
>> + int n;
>>
>> end = s->bdev_length / BDRV_SECTOR_SIZE;
>>
>> @@ -590,6 +590,8 @@ static int coroutine_fn mirror_dirty_init(MirrorBlockJob
>> *s)
>> /* Just to make sure we are not exceeding int limit. */
>> int nb_sectors = MIN(INT_MAX >> BDRV_SECTOR_BITS,
>> end - sector_num);
>> + int64_t status;
>> + BlockDriverState *file;
>>
>> mirror_throttle(s);
>>
>> @@ -597,13 +599,14 @@ static int coroutine_fn
>> mirror_dirty_init(MirrorBlockJob *s)
>> return 0;
>> }
>>
>> - ret = bdrv_is_allocated_above(bs, base, sector_num, nb_sectors, &n);
>> - if (ret < 0) {
>> - return ret;
>> + status = bdrv_get_block_status_above(bs, base, sector_num,
>> + nb_sectors, &n, &file);
>> + if (status < 0) {
>> + return status;
>> }
>>
>> assert(n > 0);
>> - if (ret == 1) {
>> + if (status & BDRV_BLOCK_DATA) {
> I think this patch would work if this was changed to something like this:
>
> mark_dirty = base == NULL ? status & BDRV_BLOCK_DATA : /* 'full'
> */
> status & BDRV_BLOCK_ALLOCATED;
>
> if (mark_dirty) {
reasonable. I have doubts with the code but was unable to
formulate. Thank you for clarifications. Will respin.
Den
