Re: [Qemu-devel] [PATCH v3 13/18] block: introduce new filter driver: fleecing-hook

[Vladimir Sementsov-Ogievskiy]

05.10.2018 18:52, Kevin Wolf wrote:
> Hi Vladimir,
>
> can you please check your mailer settings? The plain text version of the
> emails is hardly legible because it mixes quotes text and replies. I
> had to manually open the HTML part to figure out what you really wrote.

I've sent it from other thunderbird instance from home, I hope 
thunderbird at work (where I'm composing now) is ok..

>
> Am 05.10.2018 um 17:00 hat Vladimir Sementsov-Ogievskiy geschrieben:
>> Hmm, how to share children?
>>
>> backup job has two source BdrvChild'ren - child_job and child_root of
>> job blk and two target BdrvChild'ren - again, child_job and
>> child_root.
>>
>> backup_top has source child - child_backing and second - child_file
>> (named "target")..
> Right, these are six BdrvChild instances in total. I think we can ignore
> the child_job ones, they are internal to the block job infrastructure,
> so we have four of them left.
>
>> Which BdrvChild'ren you suggest to remove? They are all different.
> Now that you introduced backup_top, I think we don't need any
> BlockBackends any more. So I suggest to remove the child_root ones and
> to do all I/O through the child_backing and child_file ones of
> backup_top.
>
>> I don't know, why job needs both unnamed blk's and child_job's, and I
>> don't know is it necessary for backup to use blk's not BdrvChild'ren..
> I think we had a case recently where it turned out that it is strictly
> speaking even wrong for jobs to use BlockBackends in a function that
> intercepts a request on the BDS level (like the copy-before-write of
> backup).
>
> So getting rid of the BlockBackends isn't only okay, but actually a good
> thing by itself.
>
>> And with internal way in none-mode we'll have two unused blk's  and
>> four unused BdrvChild'ren.. Or we want to rewrite backup to use
>> BdrvChild'ren for io operations and drop child_job BdrvChild'ren? So
>> I'm lost. What did you mean?
> child_job isn't actually unused, even though you never use them to make
> requests. The child_job BdrvChild is important because of the
> BdrvChildRole callbacks it provides to the block job infrastructure.
>
> Kevin

Ok, understand, thank you for the explanation!

-- 
Best regards,
Vladimir