* Jeremy Fitzhardinge [off-list ref] wrote:

Implement a Xen back-end for hvc console.

+	cons = intf->out_cons;
+	prod = intf->out_prod;
+	mb();
+	BUG_ON((prod - cons) > sizeof(intf->out));
+
+	while ((sent < len) && ((prod - cons) < sizeof(intf->out)))
+		intf->out[MASK_XENCONS_IDX(prod++, intf->out)] = data[sent++];
+
+	wmb();
+	intf->out_prod = prod;

+	prod = intf->in_prod;
+	mb();
+	BUG_ON((prod - cons) > sizeof(intf->in));

such mb()'s are typically a sign of "i have no clear idea what SMP 
serialization rules apply here, but something is needed because 
otherwise it breaks" ?

	Ingo