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

[Max Reitz]

On 2018-02-02 14:48, Vladimir Sementsov-Ogievskiy wrote:
> 02.02.2018 16:00, Max Reitz wrote:
>> On 2018-02-02 13:07, Vladimir Sementsov-Ogievskiy wrote:
>>> 29.01.2018 18:34, Max Reitz wrote:
>>>> On 2017-11-30 17:47, Vladimir Sementsov-Ogievskiy wrote:
>>>>> Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
>>>>> ---
>>>>>    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 */
>>>> That's really not an argument.  bitmap_list_store() has to pass
>>>> QCOW2_OL_BITMAP_DIRECTORY to @ign anyway.  (Because there is no reason
>>>> not to.)
>>> in_place is a reason. When we store directory in_place, it definitely
>>> overlaps with current directory.
>> Well, then you just pass QCOW2_OL_BITMAP_DIRECTORY to @ign, which is
>> what that argument is for? :-)
> 
> hmm. but actually, I should not, because of zeroed autoclear flag. So,
> do you think, it is better to pass it, anyway?

Yes.  That flag describes what kind of metadata structures you are
planning to overwrite, and you *are* planning to overwrite the bitmap
directory, so you should set it.

Max

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