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

[Max Reitz]

On 24.07.19 11:54, Vladimir Sementsov-Ogievskiy wrote:
> 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 <address@hidden>
>>>>> ---
>>>>>    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)

OK.  I should have read the last part first, then I could have replied
sooner. :-)

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

No, I didn’t.  (Nor any of the other mails you resent.)  Weird.

Also, welcome back, congratulations, and all the best to your family! :-)

Max

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