42b36cc0ce
The virtio descriptor rings of size N-1 were nicely set up to be aligned to an N-byte boundary. But as Anthony Liguori points out, the free-running indices used by virtio require that the sizes be a power of 2, otherwise we get problems on wrap (demonstrated with lguest). So we replace the clever "2^n-1" scheme with a simple "align to page boundary" scheme: this means that all virtio rings take at least two pages, but it's safer than guessing cache alignment. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
123 lines
3.1 KiB
C
123 lines
3.1 KiB
C
#ifndef _LINUX_VIRTIO_RING_H
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#define _LINUX_VIRTIO_RING_H
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/* An interface for efficient virtio implementation, currently for use by KVM
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* and lguest, but hopefully others soon. Do NOT change this since it will
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* break existing servers and clients.
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*
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* This header is BSD licensed so anyone can use the definitions to implement
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* compatible drivers/servers.
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*
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* Copyright Rusty Russell IBM Corporation 2007. */
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#include <linux/types.h>
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/* This marks a buffer as continuing via the next field. */
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#define VRING_DESC_F_NEXT 1
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/* This marks a buffer as write-only (otherwise read-only). */
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#define VRING_DESC_F_WRITE 2
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/* This means don't notify other side when buffer added. */
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#define VRING_USED_F_NO_NOTIFY 1
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/* This means don't interrupt guest when buffer consumed. */
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#define VRING_AVAIL_F_NO_INTERRUPT 1
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/* Virtio ring descriptors: 16 bytes. These can chain together via "next". */
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struct vring_desc
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{
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/* Address (guest-physical). */
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__u64 addr;
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/* Length. */
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__u32 len;
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/* The flags as indicated above. */
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__u16 flags;
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/* We chain unused descriptors via this, too */
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__u16 next;
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};
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struct vring_avail
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{
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__u16 flags;
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__u16 idx;
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__u16 ring[];
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};
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/* u32 is used here for ids for padding reasons. */
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struct vring_used_elem
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{
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/* Index of start of used descriptor chain. */
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__u32 id;
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/* Total length of the descriptor chain which was used (written to) */
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__u32 len;
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};
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struct vring_used
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{
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__u16 flags;
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__u16 idx;
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struct vring_used_elem ring[];
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};
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struct vring {
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unsigned int num;
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struct vring_desc *desc;
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struct vring_avail *avail;
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struct vring_used *used;
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};
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/* The standard layout for the ring is a continuous chunk of memory which looks
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* like this. We assume num is a power of 2.
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*
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* struct vring
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* {
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* // The actual descriptors (16 bytes each)
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* struct vring_desc desc[num];
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*
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* // A ring of available descriptor heads with free-running index.
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* __u16 avail_flags;
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* __u16 avail_idx;
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* __u16 available[num];
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*
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* // Padding to the next page boundary.
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* char pad[];
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*
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* // A ring of used descriptor heads with free-running index.
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* __u16 used_flags;
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* __u16 used_idx;
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* struct vring_used_elem used[num];
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* };
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*/
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static inline void vring_init(struct vring *vr, unsigned int num, void *p,
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unsigned int pagesize)
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{
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vr->num = num;
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vr->desc = p;
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vr->avail = p + num*sizeof(struct vring_desc);
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vr->used = (void *)(((unsigned long)&vr->avail->ring[num] + pagesize-1)
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& ~(pagesize - 1));
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}
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static inline unsigned vring_size(unsigned int num, unsigned int pagesize)
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{
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return ((sizeof(struct vring_desc) * num + sizeof(__u16) * (2 + num)
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+ pagesize - 1) & ~(pagesize - 1))
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+ sizeof(__u16) * 2 + sizeof(struct vring_used_elem) * num;
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}
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#ifdef __KERNEL__
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#include <linux/irqreturn.h>
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struct virtio_device;
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struct virtqueue;
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struct virtqueue *vring_new_virtqueue(unsigned int num,
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struct virtio_device *vdev,
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void *pages,
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void (*notify)(struct virtqueue *vq),
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bool (*callback)(struct virtqueue *vq));
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void vring_del_virtqueue(struct virtqueue *vq);
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irqreturn_t vring_interrupt(int irq, void *_vq);
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#endif /* __KERNEL__ */
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#endif /* _LINUX_VIRTIO_RING_H */
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