Re: [Qemu-block] [Qemu-devel] [PATCH v2 1/1] include: Auto-generate the sizes lookup table

[Leonid Bloch]

On 1/10/19 2:51 PM,  wrote:
> Leonid Bloch <address@hidden> writes:
> 
>> Hi,
>>
>> On 1/8/19 2:20 PM, Kevin Wolf wrote:
>>> Am 03.01.2019 um 22:33 hat Leonid Bloch geschrieben:
>>>> The lookup table for power-of-two sizes is now auto-generated during the
>>>> build, and not hard-coded into the units.h file.
>>>>
>>>> This partially reverts commit 540b8492618eb.
>>>>
>>>> Signed-off-by: Leonid Bloch <address@hidden>
>>>
>>> During a downstream review, Max found a problem with the table that we
>>> could fix while we're touching it:
>>>
>>>       Upstream: All >= S_2GiB are not valid ints.  (qemu assumes that
>>>       sizeof(int) == 4, right?)  So S_2GiB should be 2147483648u and all
>>>       above should be ...ull or better UINT64_C().
> 
> So their (integer) type can vary.  Whether that's a problem depends on
> how the macros are used.
> 
>> But the initial reasoning for this table was to have a pure number
>> there. If there will be strings like "2147483648u/ull" or
>> "UINT64_C(...)" there, they will be stringified, literally, and will
>> appear as such inside the binary.
> 
> "Macro that expands to an integer constant that stringify() turns into a
> decimal number" is a rather peculiar contract.
> 
>>                                    If specifying the unit64 type is
>> really needed, one can always use, e.g., 2 * GiB, from units.h.
> 
> Right now I suspect these S_ macros should generally be avoided.
> 
> We have 54 of them.  I count six uses:
> 
>      block/qcow2.h:#define QCOW_MAX_REFTABLE_SIZE S_8MiB
>      block/qcow2.h:#define QCOW_MAX_L1_SIZE S_32MiB
>      block/qcow2.h:#define DEFAULT_L2_CACHE_MAX_SIZE S_32MiB
>      block/qcow2.h:#define DEFAULT_L2_CACHE_MAX_SIZE S_8MiB
>      block/qcow2.h:#define DEFAULT_CLUSTER_SIZE S_64KiB
>      block/vdi.c:#define DEFAULT_CLUSTER_SIZE S_1MiB
> 
> Which if them truly need stringify-able integers?
> 

These two:

block/qcow2.h:#define DEFAULT_CLUSTER_SIZE
block/vdi.c:#define DEFAULT_CLUSTER_SIZE.