On 11.05.20 20:16, Eric Blake wrote:
> On 5/11/20 4:21 AM, Max Reitz wrote:
>> On 08.05.20 20:03, Eric Blake wrote:
>>> Upcoming patches will enhance bitmap support in qemu-img, but in doing
>>> so, it turns out to be nice to suppress output when bitmaps make no
>>> sense (such as on a qcow2 v2 image). Add a hook to make this easier
>>> to query.
>>>
>>> In the future, when we improve the ability to look up bitmaps through
>>> a filter, we will probably also want to teach the block layer to
>>> automatically let filters pass this request on through.
>>>
>>> Signed-off-by: Eric Blake <ebl...@redhat.com>
>>> ---
>>> block/qcow2.h | 1 +
>>> include/block/block_int.h | 1 +
>>> include/block/dirty-bitmap.h | 1 +
>>> block/dirty-bitmap.c | 9 +++++++++
>>> block/qcow2-bitmap.c | 7 +++++++
>>> block/qcow2.c | 1 +
>>> 6 files changed, 20 insertions(+)
>>>
>>> diff --git a/block/qcow2.h b/block/qcow2.h
>>> index f4de0a27d5c3..fb2b2b5a7b4d 100644
>>> --- a/block/qcow2.h
>>> +++ b/block/qcow2.h
>>> @@ -764,6 +764,7 @@ bool
>>> qcow2_co_can_store_new_dirty_bitmap(BlockDriverState *bs,
>>> int qcow2_co_remove_persistent_dirty_bitmap(BlockDriverState *bs,
>>> const char *name,
>>> Error **errp);
>>> +bool qcow2_dirty_bitmap_supported(BlockDriverState *bs);
>>>
>>> ssize_t coroutine_fn
>>> qcow2_co_compress(BlockDriverState *bs, void *dest, size_t dest_size,
>>> diff --git a/include/block/block_int.h b/include/block/block_int.h
>>> index df6d0273d679..cb1082da4c43 100644
>>> --- a/include/block/block_int.h
>>> +++ b/include/block/block_int.h
>>> @@ -560,6 +560,7 @@ struct BlockDriver {
>>> uint64_t parent_perm, uint64_t
>>> parent_shared,
>>> uint64_t *nperm, uint64_t *nshared);
>>>
>>> + bool (*bdrv_dirty_bitmap_supported)(BlockDriverState *bs);
>>
>> All BDSs support bitmaps, but only some support persistent dirty
>> bitmaps, so I think the name should reflect that.
>
> How about .bdrv_dirty_bitmap_supports_persistent?Sure. Or .bdrv_supports_persistent_dirty_bitmaps. Or .bdrv_persistent_dirty_bitmaps_supported. You decide what sounds best. :) >> Conceptually, this looks reasonable. This information might indeed be >> nice to have, and I’m not sure whether we should extend any existing >> interface to return it. >> >> (The interfaces that come to my mind are: >> (1) bdrv_can_store_new_dirty_bitmap() below, which we could make accept >> a NULL @name to return basically the same information. But it’s still a >> bit different, because I’d expect that function to return whether any >> bitmap can be stored then, not whether the node supports bitmaps at all. >> So e.g. if there are already too many bitmaps, it should return false, >> even though the node itself does support bitmaps. > > [which reminds me - a while ago, we had patches for qcow2 handling with > 64k bitmaps, or whatever insane number it took to overflow data > structures, and I don't know if those ever got applied...] I think that was a1db8733d28. As far as I remember I just didn’t merge the test, because it took like five minutes to run. >> (2) bdrv_get_info()/BlockDriverInfo: This information would fit in very >> nicely here, but do we have to put it here just because it does? I >> don’t think so. This patch adds 20 lines of code, that shows that it’s >> very simple to add a dedicated method, and it’s certainly a bit easier >> to use than to invoke bdrv_get_info() and throw away all the other >> information. Perhaps this patch only shows that BlockDriverInfo doesn’t >> make much sense in the first place, and most of its fields should have >> been scalar return values from dedicated functions.) > > Indeed, you (re-)discovered some of the very reasons why I chose to make > a new interface. I could tweak the commit message to mention > alternatives, if that would help. I suppose it wouldn’t help me, but it can’t harm either. So if it isn’t too difficult, why not. Max
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