/* The standard layout for the ring is a continuous chunk of memory which * looks like this. We assume num is a power of 2. * * struct vring { * // The actual descriptors (16 bytes each) * struct vring_desc desc[num]; * * // A ring of available descriptor heads with free-running index. * __u16 avail_flags; * __u16 avail_idx; * __u16 available[num]; * * // Padding to the next align boundary. * char pad[]; * * // A ring of used descriptor heads with free-running index. * __u16 used_flags; * __u16 used_idx; * struct vring_used_elem used[num]; * }; * Note: for virtio PCI, align is 4096. */