On Tue, Aug 25, 2009 at 09:40:40PM +0930, Rusty Russell wrote:

quoted

+	u32 __user *featurep = argp;
+	int __user *fdp = argp;
+	u32 features;
+	int fd, r;
+	switch (ioctl) {
+	case VHOST_NET_SET_SOCKET:
+		r = get_user(fd, fdp);
+		if (r < 0)
+			return r;
+		return vhost_net_set_socket(n, fd);
+	case VHOST_GET_FEATURES:
+		/* No features for now */
+		features = 0;
+		return put_user(features, featurep);

We may well get more than 32 feature bits, at least for virtio_net, which will
force us to do some trickery in virtio_pci.

Unlike PCI, if we ever run out of bits we can just
add FEATURES_EXTENDED ioctl, no need for trickery.

 I'd like to avoid that here,
though it's kind of ugly.  We'd need VHOST_GET_FEATURES (and ACK) to take a
struct like:

	u32 feature_size;
	u32 features[];

Thinking about this proposal some more, how will the guest
determine the size to supply the GET_FEATURES ioctl?

Since we are a bit tight in 32 bit space already,
let's just use a 64 bit integer and be done with it?
Right?

-- 
MST