[PATCH v11 04/13] copy-on-read: pass overlay base node name to COR driver

[Vladimir Sementsov-Ogievskiy]

14.10.2020 14:57, Max Reitz wrote:
> On 14.10.20 13:09, Max Reitz wrote:
>> On 12.10.20 19:43, Andrey Shinkevich wrote:
>>> We are going to use the COR-filter for a block-stream job.
>>> To limit COR operations by the base node in the backing chain during
>>> stream job, pass the name of overlay base node to the copy-on-read
>>> driver as base node itself may change due to possible concurrent jobs.
>>> The rest of the functionality will be implemented in the patch that
>>> follows.
>>>
>>> Signed-off-by: Andrey Shinkevich <andrey.shinkevich at virtuozzo.com>
>>> ---
>>>   block/copy-on-read.c | 14 ++++++++++++++
>>>   1 file changed, 14 insertions(+)
>>
>> Is there a reason why you didn’t add this option to QAPI (as part of a
>> yet-to-be-created BlockdevOptionsCor)?  Because I’d really like it there.
>>
>>> diff --git a/block/copy-on-read.c b/block/copy-on-read.c
>>> index bcccf0f..c578b1b 100644
>>> --- a/block/copy-on-read.c
>>> +++ b/block/copy-on-read.c
>>> @@ -24,19 +24,24 @@
>>>   #include "block/block_int.h"
>>>   #include "qemu/module.h"
>>>   #include "qapi/error.h"
>>> +#include "qapi/qmp/qerror.h"
>>>   #include "qapi/qmp/qdict.h"
>>>   #include "block/copy-on-read.h"
>>>   
>>>   
>>>   typedef struct BDRVStateCOR {
>>>       bool active;
>>> +    BlockDriverState *base_overlay;
>>>   } BDRVStateCOR;
>>>   
>>>   
>>>   static int cor_open(BlockDriverState *bs, QDict *options, int flags,
>>>                       Error **errp)
>>>   {
>>> +    BlockDriverState *base_overlay = NULL;
>>>       BDRVStateCOR *state = bs->opaque;
>>> +    /* We need the base overlay node rather than the base itself */
>>> +    const char *base_overlay_node = qdict_get_try_str(options, "base");
>>
>> Shouldn’t it be called base-overlay or above-base then?
> 
> While reviewing patch 5, I realized this sould indeed be base-overlay
> (i.e. the next allocation-bearing layer above the base, not just a
> filter on top of base), but that should be noted somewhere, of course.
> Best would be the QAPI documentation for this option. O:)
> 

What about naming it just "bottom" or "bottom-node"? If we don't have base, it's strange to have something "relative to base". And we can document, that "bottom" must be a non-filter node in a backing chain of "top".


-- 
Best regards,
Vladimir