Re: [Qemu-devel] [Qemu-block] [PATCH 1/2] qcow2: add overlap check for bitmap directory

[John Snow <jsnow@redhat.com>]

On 12/07/2017 04:43 AM, Vladimir Sementsov-Ogievskiy wrote:
> 07.12.2017 01:56, John Snow wrote:
>>
>> On 11/30/2017 11:47 AM, Vladimir Sementsov-Ogievskiy wrote:
>>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>>> ---
>>>   block/qcow2.h          |  7 +++++--
>>>   block/qcow2-refcount.c | 12 ++++++++++++
>>>   block/qcow2.c          |  6 ++++++
>>>   3 files changed, 23 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/block/qcow2.h b/block/qcow2.h
>>> index 6f0ff15dd0..8f226a3609 100644
>>> --- a/block/qcow2.h
>>> +++ b/block/qcow2.h
>>> @@ -98,6 +98,7 @@
>>>   #define QCOW2_OPT_OVERLAP_SNAPSHOT_TABLE
>>> "overlap-check.snapshot-table"
>>>   #define QCOW2_OPT_OVERLAP_INACTIVE_L1 "overlap-check.inactive-l1"
>>>   #define QCOW2_OPT_OVERLAP_INACTIVE_L2 "overlap-check.inactive-l2"
>>> +#define QCOW2_OPT_OVERLAP_BITMAP_DIRECTORY
>>> "overlap-check.bitmap-directory"
>>>   #define QCOW2_OPT_CACHE_SIZE "cache-size"
>>>   #define QCOW2_OPT_L2_CACHE_SIZE "l2-cache-size"
>>>   #define QCOW2_OPT_REFCOUNT_CACHE_SIZE "refcount-cache-size"
>>> @@ -406,8 +407,9 @@ typedef enum QCow2MetadataOverlap {
>>>       QCOW2_OL_SNAPSHOT_TABLE_BITNR = 5,
>>>       QCOW2_OL_INACTIVE_L1_BITNR    = 6,
>>>       QCOW2_OL_INACTIVE_L2_BITNR    = 7,
>>> +    QCOW2_OL_BITMAP_DIRECTORY_BITNR = 8,
>>>   -    QCOW2_OL_MAX_BITNR            = 8,
>>> +    QCOW2_OL_MAX_BITNR              = 9,
>>>         QCOW2_OL_NONE           = 0,
>>>       QCOW2_OL_MAIN_HEADER    = (1 << QCOW2_OL_MAIN_HEADER_BITNR),
>>> @@ -420,12 +422,13 @@ typedef enum QCow2MetadataOverlap {
>>>       /* NOTE: Checking overlaps with inactive L2 tables will result
>>> in bdrv
>>>        * reads. */
>>>       QCOW2_OL_INACTIVE_L2    = (1 << QCOW2_OL_INACTIVE_L2_BITNR),
>>> +    QCOW2_OL_BITMAP_DIRECTORY = (1 << QCOW2_OL_BITMAP_DIRECTORY_BITNR),
>>>   } QCow2MetadataOverlap;
>>>     /* Perform all overlap checks which can be done in constant time */
>>>   #define QCOW2_OL_CONSTANT \
>>>       (QCOW2_OL_MAIN_HEADER | QCOW2_OL_ACTIVE_L1 |
>>> QCOW2_OL_REFCOUNT_TABLE | \
>>> -     QCOW2_OL_SNAPSHOT_TABLE)
>>> +     QCOW2_OL_SNAPSHOT_TABLE | QCOW2_OL_BITMAP_DIRECTORY)
>>>     /* Perform all overlap checks which don't require disk access */
>>>   #define QCOW2_OL_CACHED \
>>> diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
>>> index 3de1ab51ba..a7a2703f26 100644
>>> --- a/block/qcow2-refcount.c
>>> +++ b/block/qcow2-refcount.c
>>> @@ -2585,6 +2585,18 @@ int
>>> qcow2_check_metadata_overlap(BlockDriverState *bs, int ign, int64_t
>>> offset,
>>>           }
>>>       }
>>>   +    if ((chk & QCOW2_OL_BITMAP_DIRECTORY) &&
>>> +        (s->autoclear_features & QCOW2_AUTOCLEAR_BITMAPS))
>>> +    {
>>> +        /* update_ext_header_and_dir_in_place firstly drop autoclear
>>> flag,
>>> +         * so it will not fail */
>>> +        if (overlaps_with(s->bitmap_directory_offset,
>>> +                          s->bitmap_directory_size))
>>> +        {
>>> +            return QCOW2_OL_BITMAP_DIRECTORY;
>>> +        }
>>> +    }
>>> +
>> Isn't the purpose of this function to test if a given offset conflicts
>> with known regions of the file? I don't see you actually utilize the
>> 'offset' parameter here, but maybe I don't understand what you're trying
>> to accomplish.
> 
> #define overlaps_with(ofs, sz) \
>     ranges_overlap(offset, size, ofs, sz)
> 
> I've just copied one of similar blocks in qcow2_check_metadata_overlap()
> 

Sigh, I didn't realize that was a macro. I don't really like lowercase
macros, but you didn't add it.

Reviewed-by: John Snow <jsnow@redhat.com>

Carry on...