Re: [Qemu-devel] [PATCH 2/4] block/dirty-bitmap: add hide/unhide API

[Vladimir Sementsov-Ogievskiy]

08.06.2019 1:39, John Snow wrote:
> 
> 
> On 6/3/19 8:00 AM, Vladimir Sementsov-Ogievskiy wrote:
>> Add functionality to make bitmap temporary anonymous. It will be used
>> to implement bitmap remove transaction action. We need hide bitmap
>> persistence too, as there are should not be unnamed persistent bitmaps.
>>
> 
> Ah, so this effectively ... "hides" a bitmap from any further
> transaction actions. It also "hides" it from getting flushed to disk...
> sort of?
> 
> The outer loop in store works with bdrv_dirty_bitmap_next, and we'll
> skip this bitmap because it's anonymous/not persistent.
> 
> There's a second loop where we iterate bm_list, and we'll skip storing
> this bitmap because that entry won't have an in-memory bitmap associated
> with it in bm_list.
> 
> ...But then we'll call update_ext_header_and_dir with the stale entries
> in bm_list?

Hidden is a temprory state, so, we should not go to close() in this state.
It's a state inside a transaction.

Stale entries in list will be marked IN_USE anyway, so there is no damage 
anyway.

> 
>> Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
>> ---
>>   include/block/dirty-bitmap.h |  2 ++
>>   block/dirty-bitmap.c         | 26 ++++++++++++++++++++++++++
>>   2 files changed, 28 insertions(+)
>>
>> diff --git a/include/block/dirty-bitmap.h b/include/block/dirty-bitmap.h
>> index 8044ace63e..542e437123 100644
>> --- a/include/block/dirty-bitmap.h
>> +++ b/include/block/dirty-bitmap.h
>> @@ -116,5 +116,7 @@ bool bdrv_dirty_bitmap_next_dirty_area(BdrvDirtyBitmap 
>> *bitmap,
>>   BdrvDirtyBitmap *bdrv_reclaim_dirty_bitmap_locked(BlockDriverState *bs,
>>                                                     BdrvDirtyBitmap *bitmap,
>>                                                     Error **errp);
>> +void bdrv_dirty_bitmap_hide(BdrvDirtyBitmap *bitmap);
>> +void bdrv_dirty_bitmap_unhide(BdrvDirtyBitmap *bitmap);
>>   
>>   #endif
>> diff --git a/block/dirty-bitmap.c b/block/dirty-bitmap.c
>> index 49646a30e6..592964635e 100644
>> --- a/block/dirty-bitmap.c
>> +++ b/block/dirty-bitmap.c
>> @@ -35,6 +35,10 @@ struct BdrvDirtyBitmap {
>>       bool busy;                  /* Bitmap is busy, it can't be used via 
>> QMP */
>>       BdrvDirtyBitmap *successor; /* Anonymous child, if any. */
>>       char *name;                 /* Optional non-empty unique ID */
>> +    char *hidden_name;          /* Backup of @name for removal transaction
>> +                                   action. Used for hide/unhide API. */
>> +    bool hidden_persistent;     /* Backup of @persistent for removal 
>> transaction
>> +                                   action. */
>>       int64_t size;               /* Size of the bitmap, in bytes */
>>       bool disabled;              /* Bitmap is disabled. It ignores all 
>> writes to
>>                                      the device */
>> @@ -849,3 +853,25 @@ out:
>>           qemu_mutex_unlock(src->mutex);
>>       }
>>   }
>> +
>> +void bdrv_dirty_bitmap_hide(BdrvDirtyBitmap *bitmap)
>> +{
>> +    qemu_mutex_lock(bitmap->mutex);
>> +    assert(!bitmap->hidden_name);
>> +    bitmap->hidden_name = bitmap->name;
>> +    bitmap->hidden_persistent = bitmap->persistent;
>> +    bitmap->name = NULL;
>> +    bitmap->persistent = false;
>> +    qemu_mutex_unlock(bitmap->mutex);
>> +}
>> +
>> +void bdrv_dirty_bitmap_unhide(BdrvDirtyBitmap *bitmap)
>> +{
>> +    qemu_mutex_lock(bitmap->mutex);
>> +    assert(!bitmap->name);
>> +    bitmap->name = bitmap->hidden_name;
>> +    bitmap->persistent = bitmap->hidden_persistent;
>> +    bitmap->hidden_name = NULL;
>> +    bitmap->hidden_persistent = false;
>> +    qemu_mutex_unlock(bitmap->mutex);
>> +}
>>


-- 
Best regards,
Vladimir