Commit b28e0506 authored Dec 25, 2014 by Michael S. Tsirkin

virtio_ring: document alignment requirements



Host needs to know vring element alignment requirements:
simply doing alignof on structures doesn't work reliably: on some
platforms gcc has alignof(uint32_t) == 2.

Add macros for alignment as specified in virtio 1.0 cs01,
export them to userspace as well.

Acked-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

parent b7392d22

include/uapi/linux/virtio_ring.h

+7 −0

Original line number	Diff line number	Diff line
		@@ -101,6 +101,13 @@ struct vring {
		struct vring_used *used;
		};

		/* Alignment requirements for vring elements.
		* When using pre-virtio 1.0 layout, these fall out naturally.
		*/
		#define VRING_AVAIL_ALIGN_SIZE 2
		#define VRING_USED_ALIGN_SIZE 4
		#define VRING_DESC_ALIGN_SIZE 16

		/* The standard layout for the ring is a continuous chunk of memory which looks
		* like this. We assume num is a power of 2.
		*