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

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Jan 16, 2017 at 08:58:34PM +0530, Bhumika Goyal wrote:
> On Mon, Jan 16, 2017 at 7:59 PM, Michael S. Tsirkin <mst@redhat.com> 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?
> >
> 
> Ideally after making the structure const, bytes should move from the
> data to the text segment of the memory. So a shift in the number of
> bytes should be seen in the size details of the.o file after compiling
> the changes. But for this patch no shift in bytes took place before
> and after applying the changes.
> 
> Thanks,
> Bhumika
> 
> >> ---
> >>  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

Could that be because of alignment?
I'd say a list of symbols in each section would be
a better indication of what happened.

-- 
MST