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

[Max Reitz <mreitz@redhat.com>]

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On 14.10.20 16:56, Vladimir Sementsov-Ogievskiy wrote:
> 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@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

(Just realized that sounds different from how I meant it.  I meant that
 “above-base” would be wrong, so from the two, if any, it should 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".

Works for me, too.

Max


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