Re: [PULL 5/5] virtio/s390: virtio: constify virtio_config_ops structures

[Christian Borntraeger <borntraeger@de.ibm.com>]

On 01/16/2017 03:29 PM, Michael S. Tsirkin wrote:
> On Mon, Jan 16, 2017 at 03:04:33PM +0100, Cornelia Huck wrote:
>> From: Bhumika Goyal <bhumirks@gmail.com>
>>
>> Declare virtio_config_ops structure as const as it is only stored in the
>> config field of a virtio_device structure. This field is of type const, so
>> virtio_config_ops structures having this property can be declared const.
>> Done using Coccinelle:
>>
>> @r1 disable optional_qualifier@
>> identifier i;
>> position p;
>> @@
>> static struct virtio_config_ops i@p={...};
>>
>> @ok1@
>> identifier r1.i;
>> position p;
>> struct virtio_ccw_device x;
>> @@
>> x.vdev.config=&i@p
>>
>> @bad@
>> position p!={r1.p,ok1.p};
>> identifier r1.i;
>> @@
>> i@p
>>
>> @depends on !bad disable optional_qualifier@
>> identifier r1.i;
>> @@
>> +const
>> struct virtio_config_ops i;
>>
>> File size before and after applying the patch remains the same.
>> text	data	bss	dec	hex   filename
>> 9235	296	32928	42459	a5db  drivers/s390/virtio/virtio_ccw.o
>>
>> Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
>> Message-Id: <1484333336-13443-1-git-send-email-bhumirks@gmail.com>
>> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
>> Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
> 
> I am frankly puzzled by this reporting on file sizes.
> So what does it mean that it's the same?

I think it means that the compiler cannot make any additional optimization
due to that being const. It still seems the right thing to do.

> 
>> ---
>>  drivers/s390/virtio/virtio_ccw.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/s390/virtio/virtio_ccw.c b/drivers/s390/virtio/virtio_ccw.c
>> index 0672c6234ae8..070c4da95f48 100644
>> --- a/drivers/s390/virtio/virtio_ccw.c
>> +++ b/drivers/s390/virtio/virtio_ccw.c
>> @@ -944,7 +944,7 @@ static void virtio_ccw_set_status(struct virtio_device *vdev, u8 status)
>>  	kfree(ccw);
>>  }
>>  
>> -static struct virtio_config_ops virtio_ccw_config_ops = {
>> +static const struct virtio_config_ops virtio_ccw_config_ops = {
>>  	.get_features = virtio_ccw_get_features,
>>  	.finalize_features = virtio_ccw_finalize_features,
>>  	.get = virtio_ccw_get_config,
>> -- 
>> 2.11.0
>