[libvirt] [PATCH 18/35] qemu: block: Always set discard for storage nodes

[John Ferlan]

On 05/02/2018 03:39 PM, John Ferlan wrote:
> 
> 
> On 04/25/2018 11:15 AM, Peter Krempa wrote:
>> Enabling discard for the storage node allows the format drivers to
>> discard snapshots and other things, while configuration of the format
>> layer actually decides whether to actually discard data on request from
>> the host.
>>
>> Signed-off-by: Peter Krempa <pkrempa at redhat.com>
>> ---
>>  src/qemu/qemu_block.c | 5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>
> 
> Isn't this related to the {disk|src}->discard value? Which we copied
> from patch 3.
> 
> So you'd just be unconditionally setting here regardless of what was
> configured?
> 
> 
> John
> 


Hmm... so it seems the answer to my question is in the next patch.

TBH: The variation between names and knowing exactly which method is for
what condition - it's well, mind boggling. The terminology of storage
and format layer to go along with source source protocol and storage
node without much code documenting makes things challenging to follow.

So it seems for whatever reason this GetBackendProps is always wanting
to use "unmap"; whereas, GetBlockdevFormatCommonProps may use "unmap" or
"ignore".  And then, in the next patch a blockdev props and a backend
props are both generated for the same object - poof.

So assuming this dance is correct,

Reviewed-by: John Ferlan <jferlan at redhat.com>

John