From 0a8a69dd77ddbd4513b21363021ecde7e1025502 Mon Sep 17 00:00:00 2001 From: Rusty Russell Date: Mon, 22 Oct 2007 11:03:40 +1000 Subject: Virtio helper routines for a descriptor ringbuffer implementation These helper routines supply most of the virtqueue_ops for hypervisors which want to use a ring for virtio. Unlike the previous lguest implementation: 1) The rings are variable sized (2^n-1 elements). 2) They have an unfortunate limit of 65535 bytes per sg element. 3) The page numbers are always 64 bit (PAE anyone?) 4) They no longer place used[] on a separate page, just a separate cacheline. 5) We do a modulo on a variable. We could be tricky if we cared. 6) Interrupts and notifies are suppressed using flags within the rings. Users need only get the ring pages and provide a notify hook (KVM wants the guest to allocate the rings, lguest does it sanely). Signed-off-by: Rusty Russell Cc: Dor Laor --- include/linux/virtio_ring.h | 119 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 119 insertions(+) create mode 100644 include/linux/virtio_ring.h (limited to 'include') diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h new file mode 100644 index 000000000000..ac69e7bb5a14 --- /dev/null +++ b/include/linux/virtio_ring.h @@ -0,0 +1,119 @@ +#ifndef _LINUX_VIRTIO_RING_H +#define _LINUX_VIRTIO_RING_H +/* An interface for efficient virtio implementation, currently for use by KVM + * and lguest, but hopefully others soon. Do NOT change this since it will + * break existing servers and clients. + * + * This header is BSD licensed so anyone can use the definitions to implement + * compatible drivers/servers. + * + * Copyright Rusty Russell IBM Corporation 2007. */ +#include + +/* This marks a buffer as continuing via the next field. */ +#define VRING_DESC_F_NEXT 1 +/* This marks a buffer as write-only (otherwise read-only). */ +#define VRING_DESC_F_WRITE 2 + +/* This means don't notify other side when buffer added. */ +#define VRING_USED_F_NO_NOTIFY 1 +/* This means don't interrupt guest when buffer consumed. */ +#define VRING_AVAIL_F_NO_INTERRUPT 1 + +/* Virtio ring descriptors: 16 bytes. These can chain together via "next". */ +struct vring_desc +{ + /* Address (guest-physical). */ + __u64 addr; + /* Length. */ + __u32 len; + /* The flags as indicated above. */ + __u16 flags; + /* We chain unused descriptors via this, too */ + __u16 next; +}; + +struct vring_avail +{ + __u16 flags; + __u16 idx; + __u16 ring[]; +}; + +/* u32 is used here for ids for padding reasons. */ +struct vring_used_elem +{ + /* Index of start of used descriptor chain. */ + __u32 id; + /* Total length of the descriptor chain which was used (written to) */ + __u32 len; +}; + +struct vring_used +{ + __u16 flags; + __u16 idx; + struct vring_used_elem ring[]; +}; + +struct vring { + unsigned int num; + + struct vring_desc *desc; + + struct vring_avail *avail; + + struct vring_used *used; +}; + +/* The standard layout for the ring is a continuous chunk of memory which looks + * like this. The used fields will be aligned to a "num+1" boundary. + * + * 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 so a correctly-chosen num value will cache-align used_idx. + * char pad[sizeof(struct vring_desc) - sizeof(avail_flags)]; + * + * // A ring of used descriptor heads with free-running index. + * __u16 used_flags; + * __u16 used_idx; + * struct vring_used_elem used[num]; + * }; + */ +static inline void vring_init(struct vring *vr, unsigned int num, void *p) +{ + vr->num = num; + vr->desc = p; + vr->avail = p + num*sizeof(struct vring); + vr->used = p + (num+1)*(sizeof(struct vring) + sizeof(__u16)); +} + +static inline unsigned vring_size(unsigned int num) +{ + return (num + 1) * (sizeof(struct vring_desc) + sizeof(__u16)) + + sizeof(__u32) + num * sizeof(struct vring_used_elem); +} + +#ifdef __KERNEL__ +#include +struct virtio_device; +struct virtqueue; + +struct virtqueue *vring_new_virtqueue(unsigned int num, + struct virtio_device *vdev, + void *pages, + void (*notify)(struct virtqueue *vq), + bool (*callback)(struct virtqueue *vq)); +void vring_del_virtqueue(struct virtqueue *vq); + +irqreturn_t vring_interrupt(int irq, void *_vq); +#endif /* __KERNEL__ */ +#endif /* _LINUX_VIRTIO_RING_H */ -- cgit v1.2.2