Re: [Qemu-devel] [PATCH 09/21] qcow2: Open images with refcount order != 4

[Max Reitz <mreitz@redhat.com>]

On 2014-11-10 at 18:03, Eric Blake wrote:
> On 11/10/2014 06:45 AM, Max Reitz wrote:
>> No longer refuse to open images with a different refcount entry width
>> than 16 bits; only reject images with a refcount width larger than 64
>> bits (which is prohibited by the specification).
>>
>> Signed-off-by: Max Reitz <mreitz@redhat.com>
>> ---
>>   block/qcow2.c | 8 ++++----
>>   1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/block/qcow2.c b/block/qcow2.c
>> index d70e927..b718e75 100644
>> --- a/block/qcow2.c
>> +++ b/block/qcow2.c
>> @@ -677,10 +677,10 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
>>       }
>>   
>>       /* Check support for various header values */
>> -    if (header.refcount_order != 4) {
>> -        report_unsupported(bs, errp, "%d bit reference counts",
>> -                           1 << header.refcount_order);
>> -        ret = -ENOTSUP;
>> +    if (header.refcount_order > 6) {
>> +        error_setg(errp, "Reference count entry width too large (%i bit); may "
>> +                   "not exceed 64 bit", 1 << header.refcount_order);
> Overflows if I fuzz an image to put 32 or larger into
> header.refcount_order. It may be better to just tweak the error message
> to state that the order cannot exceed 6, rather than trying to display
> the actual bit width that the user is requesting, as then you avoid the
> '1 << problem'.

Yes, probably. Or we display it in binary: "0b1%0*i", 
header.refcount_order, 0 (which works since refcount_order is guaranteed 
to exceed 6).

Joking aside, yes, I'll omit the theoretical refcount width.

Max