Re: [Qemu-block] [PATCH RFC 1/1] Stream block job involves copy-on-read filter

[Andrey Shinkevich]

On 08/02/2019 16:13, Alberto Garcia wrote:
> On Wed 23 Jan 2019 12:54:24 PM CET, Andrey Shinkevich wrote:
>> +static BlockDriverState *insert_filter(BlockDriverState *bs, Error **errp)
>> +{
>> +    BlockDriverState *cor_filter_bs;
>> +    Error *local_err = NULL;
>> +
>> +    cor_filter_bs = create_filter_node(bs, errp);
>> +    if (cor_filter_bs == NULL) {
>> +        error_prepend(errp, "Could not create filter node: ");
>> +        return NULL;
>> +    }
>> +
>> +    bdrv_set_aio_context(cor_filter_bs, bdrv_get_aio_context(bs));
>> +
>> +    bdrv_drained_begin(bs);
>> +    bdrv_replace_node(bs, cor_filter_bs, &local_err);
>> +    bdrv_drained_end(bs);
> 
> I think this was already discussed in the previous version of this
> patch: if you insert a copy-on-read filter here then all guest reads
> will copy the data from the backing chain, but you don't want to copy
> anything below the 'base' node, so the copy-on-read filter needs a
> 'base' parameter.
> 
> Berto
> 
Thank you, Alberto. We will sort it out for sure.
Before that, we still have the unresolved issue with getting the filter
as the 'base' input parameter. That happens sometimes because the base
is being searched by the file name, which is the same to the one of the
filter, rather than by the node name (!). The given series is a some
sort of workaround.
We are looking forward to hearing from the maintainers how to improve
the solution. Is there any idea?
-- 
With the best regards,
Andrey Shinkevich