Re: [PATCH v7 14/47] stream: Deal with filters

[Max Reitz]

On 18.08.20 16:28, Kevin Wolf wrote:
> Am 25.06.2020 um 17:21 hat Max Reitz geschrieben:
>> Because of the (not so recent anymore) changes that make the stream job
>> independent of the base node and instead track the node above it, we
>> have to split that "bottom" node into two cases: The bottom COW node,
>> and the node directly above the base node (which may be an R/W filter
>> or the bottom COW node).
>>
>> Signed-off-by: Max Reitz <mreitz@redhat.com>
>> ---
>>  qapi/block-core.json |  4 +++
>>  block/stream.c       | 63 ++++++++++++++++++++++++++++++++------------
>>  blockdev.c           |  4 ++-
>>  3 files changed, 53 insertions(+), 18 deletions(-)
>>
>> diff --git a/qapi/block-core.json b/qapi/block-core.json
>> index b20332e592..df87855429 100644
>> --- a/qapi/block-core.json
>> +++ b/qapi/block-core.json
>> @@ -2486,6 +2486,10 @@
>>  # On successful completion the image file is updated to drop the backing 
>> file
>>  # and the BLOCK_JOB_COMPLETED event is emitted.
>>  #
>> +# In case @device is a filter node, block-stream modifies the first 
>> non-filter
>> +# overlay node below it to point to base's backing node (or NULL if @base 
>> was
>> +# not specified) instead of modifying @device itself.
> 
> Not to @base's backing node, but to @base itself (or actually, to
> above_base's backing node, which is initially @base, but may have
> changed when the job is completed).

Oh, yes.

(I thought I had noticed that already at some point and fixed it
locally...  But apparently not.)

> Should we also document what using a filter node for @base means?

Hm.  What does it mean?  I think the more interesting case is what it
means if above_base is a filter, right?

Maybe we can put in somewhere in the “If a base file is specified then
sectors are not copied from that base file and its backing chain.”  But
the more I think about it, the less I know what we could add to it.
What happens if there are filters above @base is that their data isn’t
copied, because that’s exactly the data in @base.

Max

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