Re: [Qemu-devel] [PATCH v5 00/42] block: Deal with filters

[Max Reitz <mreitz@redhat.com>]

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On 13.06.19 17:28, Vladimir Sementsov-Ogievskiy wrote:
> 13.06.2019 1:09, Max Reitz wrote:
>> Hi,
>>
>> When we introduced filters, we did it a bit casually.  Sure, we talked a
>> lot about them before, but that was mostly discussion about where
>> implicit filters should be added to the graph (note that we currently
>> only have two implicit filters, those being mirror and commit).  But in
>> the end, we really just designated some drivers filters (Quorum,
>> blkdebug, etc.) and added some specifically (throttle, COR), without
>> really looking through the block layer to see where issues might occur.
>>
>> It turns out vast areas of the block layer just don’t know about filters
>> and cannot really handle them.  Many cases will work in practice, in
>> others, well, too bad, you cannot use some feature because some part
>> deep inside the block layer looks at your filters and thinks they are
>> format nodes.
>>
>> This is one reason why this series is needed.  Over time (since v1), a
>> second reason has made its way in:
>>
>> bs->file is not necessarily the place where a node’s data is stored.
>> qcow2 now has external data files, and currently there is no way for the
>> general block layer to know that the data is not stored in bs->file.
>> Right now, I do not think that has any real consequences (all functions
>> that need access to the actual data storage file should only do so as a
>> fallback if the driver does not provide some functionality, but qcow2
>> should provide it all), but it still shows that we need some way to let
>> the general block layer know about such data files.  (Also, I will need
>> this for v1 of my “Inquire images’ rotational info” series.)
>>
>> I won’t go on and on about this series now, I think the patches pretty
>> much speak for themselves now.  If the cover letter gets too long,
>> nobody reads it anyway (see previous versions).
>>
>>
>> *** This series depends on some others. ***
>>
>> Dependencies:
>> - [PATCH 0/4] block: Keep track of parent quiescing
>> - [PATCH 0/2] vl: Drain before (block) job cancel when quitting
>> - [PATCH v2 0/2] blockdev: Overlays are not snapshots
>>
>> Based-on: <20190605161118.14544-1-mreitz@redhat.com>
>> Based-on: <20190612220839.1374-1-mreitz@redhat.com>
>> Based-on: <20190603202236.1342-1-mreitz@redhat.com>
> 
> Could you please export a branch?

Sure:

https://git.xanclic.moe/XanClic/qemu child-access-functions-v5
Or:
https://github.com/XanClic/qemu child-access-functions-v5


(And the base branch is:

https://git.xanclic.moe/XanClic/qemu child-access-functions-base
https://github.com/XanClic/qemu child-access-functions-base
)

>> v5:
>> - Split the huge patches 2 and 3 from the previous version into many
>>    smaller patches to maintain the potential reviewers’ sanity [Vladimir]
> 
> Thank you! In spite of frightening amount of patches, reviewing became a lot
> simpler.

I had hoped making it exactly 42 patches would make it a bit more welcoming.

Again, thanks a lot for reviewing!

Max


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