[Qemu-devel] Re: [PATCH, RFC] virtio_blk: add cache control support

[Christoph Hellwig]

On Wed, Mar 16, 2011 at 02:39:39PM +1030, Rusty Russell wrote:
> > +   if (strncmp(buf, "write through", sizeof("write through") - 1) == 0) {
> > +           ;
> > +   } else if (strncmp(buf, "write back", sizeof("write back") - 1) == 0) {
> 
>    Is there a reason we're not letting gcc and/or strcmp do the
> optimization work here?

I'm happ to switch strcmp.

> > +   vdev->config->set(vdev, offsetof(struct virtio_blk_config, features),
> > +                     &features, sizeof(features));
> > +
> > +   vdev->config->get(vdev, offsetof(struct virtio_blk_config, features),
> > +                     &features2, sizeof(features2));
> > +
> > +   if ((features & VIRTIO_BLK_RT_WCE) !=
> > +       (features2 & VIRTIO_BLK_RT_WCE))
> > +           return -EIO;
> 
>    This seems like a debugging check you left in.  Or do you suspect
> some issues?

No, it's intentional.  config space writes can't return errors, so we need
to check that the value has really changed.  I'll add a comment explaining it.