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

[Rusty Russell]

On Tue, 15 Mar 2011 15:16:44 +0100, Christoph Hellwig <h...@lst.de> wrote:
> Add support for the new dynamic features config space field to allow
> en/disabling the write cache at runtime.  The userspace interface is
> a SCSI-compatible sysfs attribute.
> 
> Signed-off-by: Christoph Hellwig <h...@lst.de>

Hi Christoph,

   Neat work.  Minor comments:

> +     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?

> +     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?

Thanks,
Rusty.