Re: [Qemu-devel] [PATCH v5 30/42] qemu-img: Use child access functions

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

21.06.2019 16:15, Vladimir Sementsov-Ogievskiy wrote:
> 19.06.2019 18:49, Max Reitz wrote:
>> On 19.06.19 11:18, Vladimir Sementsov-Ogievskiy wrote:
>>> 13.06.2019 1:09, Max Reitz wrote:
>>>> This changes iotest 204's output, because blkdebug on top of a COW node
>>>> used to make qemu-img map disregard the rest of the backing chain (the
>>>> backing chain was broken by the filter).  With this patch, the
>>>> allocation in the base image is reported correctly.
>>>>
>>>> Signed-off-by: Max Reitz <mreitz@redhat.com>
>>>> ---
>>>>    qemu-img.c                 | 36 ++++++++++++++++++++----------------
>>>>    tests/qemu-iotests/204.out |  1 +
>>>>    2 files changed, 21 insertions(+), 16 deletions(-)
>>>>
>>>> diff --git a/qemu-img.c b/qemu-img.c
>>>> index 07b6e2a808..7bfa6e5d40 100644
>>>> --- a/qemu-img.c
>>>> +++ b/qemu-img.c
>>>> @@ -992,7 +992,7 @@ static int img_commit(int argc, char **argv)
>>>>        if (!blk) {
>>>>            return 1;
>>>>        }
>>>> -    bs = blk_bs(blk);
>>>> +    bs = bdrv_skip_implicit_filters(blk_bs(blk));
>>>
>>> if filename is json, describing explicit filter over normal node, bs will be
>>> explicit filter ...
>>>
>>>>        qemu_progress_init(progress, 1.f);
>>>>        qemu_progress_print(0.f, 100);
>>>> @@ -1009,7 +1009,7 @@ static int img_commit(int argc, char **argv)
>>>>            /* This is different from QMP, which by default uses the deepest file in
>>>>             * the backing chain (i.e., the very base); however, the traditional
>>>>             * behavior of qemu-img commit is using the immediate backing file. */
>>>> -        base_bs = backing_bs(bs);
>>>> +        base_bs = bdrv_filtered_cow_bs(bs);
>>>>            if (!base_bs) {
>>>
>>> and here we'll fail.
>>
>> Right, will change to bdrv_backing_chain_next().
>>
>>>>                error_setg(&local_err, "Image does not have a backing file");
>>>>                goto done;
>>>> @@ -1626,19 +1626,18 @@ static int convert_iteration_sectors(ImgConvertState *s, int64_t sector_num)
>>>>        if (s->sector_next_status <= sector_num) {
>>>>            int64_t count = n * BDRV_SECTOR_SIZE;
>>>> +        BlockDriverState *src_bs = blk_bs(s->src[src_cur]);
>>>> +        BlockDriverState *base;
>>>>            if (s->target_has_backing) {
>>>> -
>>>> -            ret = bdrv_block_status(blk_bs(s->src[src_cur]),
>>>> -                                    (sector_num - src_cur_offset) *
>>>> -                                    BDRV_SECTOR_SIZE,
>>>> -                                    count, &count, NULL, NULL);
>>>> +            base = bdrv_backing_chain_next(src_bs);
>>>
>>> As you described in another patch, will not we here get allocated in base as allocated, because of
>>> counting filters above base?
>>
>> Damn, yes.  So
>>
>>      base = bdrv_filtered_cow_bs(bdrv_skip_rw_filters(src_bs));
>>
>> I suppose.
>>
>>> Hmm. I now think, why filters don't report everything as unallocated, would not it be more correct
>>> than fallthrough to child?
>>
>> I don’t know, actually.  Maybe, maybe not.
>>
>>>>            } else {
>>>> -            ret = bdrv_block_status_above(blk_bs(s->src[src_cur]), NULL,
>>>> -                                          (sector_num - src_cur_offset) *
>>>> -                                          BDRV_SECTOR_SIZE,
>>>> -                                          count, &count, NULL, NULL);
>>>> +            base = NULL;
>>>>            }
>>>> +        ret = bdrv_block_status_above(src_bs, base,
>>>> +                                      (sector_num - src_cur_offset) *
>>>> +                                      BDRV_SECTOR_SIZE,
>>>> +                                      count, &count, NULL, NULL);
>>>>            if (ret < 0) {
>>>>                error_report("error while reading block status of sector %" PRId64
>>>>                             ": %s", sector_num, strerror(-ret));
>>
>> [...]
>>
>>>> @@ -2949,7 +2950,7 @@ static int img_map(int argc, char **argv)
>>>>        if (!blk) {
>>>>            return 1;
>>>>        }
>>>> -    bs = blk_bs(blk);
>>>> +    bs = bdrv_skip_implicit_filters(blk_bs(blk));
>>>
>>> Hmm, another thought about implicit filters, how they could be here in qemu-img?
>>
>> Hm, I don’t think they can.
>>
>>> If implicit are only
>>> job filters. Do you prepared it for implicit COR? But we discussed with Kevin that we'd better deprecate
>>> copy-on-read option..
>>>
>>> So, if implicit filters are for compatibility, we'll have them only in block-jobs. So, seems no reason to support
>>> them in qemu-img.
>>
>> Seems reasonable, yes.
>>
>>> Also, in block-jobs, we can abandon creating implicit filters above any filter nodes, as well as abandon creating any
>>> filter nodes above implicit filters. This will still support old scenarios, but gives very simple and well defined scope
>>> of using implicit filters and how to work with them. What do you think?
>>
>> Hm, in what way would that make things simpler?
>>
> 
> This question was in my mind while I've finishing this paragraph) At least such restriction answer the question, where
> should new filters be added: below or under implicit filters.. With such restriction we always can have only one implicit filter
> over non-filter node, and above it should be explicit filter or non-filter node. But this need huge work to be done with small
> benefit, so, forget it)
> 
> 

Strange, I have this mail automatically returned back. Did you receive it?

-- 
Best regards,
Vladimir