Re: [Qemu-devel] [RFC PATCH 07/12] qcow2-bitmap: add basic bitmaps info

[John Snow <jsnow@redhat.com>]

On 05/14/2018 11:12 AM, Vladimir Sementsov-Ogievskiy wrote:
> 12.05.2018 04:25, John Snow wrote:
>> Add functions for querying the basic information inside of bitmaps.
>> Restructure the bitmaps flags masks to facilitate providing a list of
>> flags belonging to the bitmap(s) being queried.
>>
>> Signed-off-by: John Snow <jsnow@redhat.com>
>> ---
>>   block/qcow2-bitmap.c | 81
>> ++++++++++++++++++++++++++++++++++++++++++++++++++--
>>   block/qcow2.c        |  7 +++++
>>   block/qcow2.h        |  1 +
>>   3 files changed, 87 insertions(+), 2 deletions(-)
>>
>> diff --git a/block/qcow2-bitmap.c b/block/qcow2-bitmap.c
>> index 60e01abfd7..811b82743a 100644
>> --- a/block/qcow2-bitmap.c
>> +++ b/block/qcow2-bitmap.c
>> @@ -49,8 +49,28 @@
>>     /* Bitmap directory entry flags */
>>   #define BME_RESERVED_FLAGS 0xfffffffcU
>> -#define BME_FLAG_IN_USE (1U << 0)
>> -#define BME_FLAG_AUTO   (1U << 1)
>> +
>> +enum BME_FLAG_BITS {
>> +    BME_FLAG_BIT__BEGIN = 0,
>> +    BME_FLAG_BIT_IN_USE = BME_FLAG_BIT__BEGIN,
>> +    BME_FLAG_BIT_AUTO   = 1,
>> +    BME_FLAG_BIT_EXTRA  = 2,
>> +    BME_FLAG_BIT__MAX,
>> +};
>> +
>> +#define BME_FLAG_IN_USE (1U << BME_FLAG_BIT_IN_USE)
>> +#define BME_FLAG_AUTO   (1U << BME_FLAG_BIT_AUTO)
>> +#define BME_FLAG_EXTRA  (1U << BME_FLAG_BIT_EXTRA)
>> +
>> +/* Correlate canonical spec values to autogenerated QAPI values */
>> +struct {
>> +    uint32_t mask;
> 
> mask is unused in this patch
> 
>> +    int qapi_value;
>> +} BMEFlagMap[BME_FLAG_BIT__MAX] = {
>> +    [BME_FLAG_BIT_IN_USE] = { BME_FLAG_IN_USE,
>> BITMAP_FLAG_ENUM_IN_USE },
>> +    [BME_FLAG_BIT_AUTO]   = { BME_FLAG_AUTO,   BITMAP_FLAG_ENUM_AUTO },
>> +    [BME_FLAG_BIT_EXTRA]  = { BME_FLAG_EXTRA, 
>> BITMAP_FLAG_ENUM_EXTRA_DATA_COMPATIBLE },
>> +};
>>     /* bits [1, 8] U [56, 63] are reserved */
>>   #define BME_TABLE_ENTRY_RESERVED_MASK 0xff000000000001feULL
>> @@ -663,6 +683,63 @@ static void del_bitmap_list(BlockDriverState *bs)
>>       }
>>   }
>>   +static BitmapFlagEnumList *get_bitmap_flags(uint32_t flags)
>> +{
>> +    int i;
>> +    BitmapFlagEnumList *flist = NULL;
>> +    BitmapFlagEnumList *ftmp;
>> +
>> +    while (flags) {
>> +        i = ctz32(flags);
>> +        ftmp = g_new0(BitmapFlagEnumList, 1);
>> +        if (i >= BME_FLAG_BIT__BEGIN && i < BME_FLAG_BIT__MAX) {
>> +            ftmp->value = BMEFlagMap[i].qapi_value;
>> +        } else {
>> +            ftmp->value = BITMAP_FLAG_ENUM_UNKNOWN;
> 
> so, there may be several "unknown" entries. It's inconsistent with
> "@unknown: This bitmap has unknown or reserved properties.".
> 
> Finally, can we export values for unknown flags? It should be more
> informative.
> 

I changed my mind -- qemu-img is not a debugging tool and shouldn't get
lost in the weeds trying to enumerate the different kinds of reserved
values that are set.

It's an error to have them set, or not -- which ones specifically is not
information that an end-user need know or care about, and I don't want
to create an extra structure to contain the value.

I'm going to rewrite this loop to just only ever have one unknown value
at a maximum.

--js