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Diffstat (limited to 'virtio-ring.h')
| -rw-r--r-- | virtio-ring.h | 164 |
1 files changed, 164 insertions, 0 deletions
diff --git a/virtio-ring.h b/virtio-ring.h new file mode 100644 index 0000000..7506a97 --- /dev/null +++ b/virtio-ring.h @@ -0,0 +1,164 @@ +#ifndef VIRTIO_RING_H +#define VIRTIO_RING_H +/* An interface for efficient virtio implementation. + * + * This header is BSD licensed so anyone can use the definitions + * to implement compatible drivers/servers. + * + * Copyright 2007, 2009, IBM Corporation + * Copyright 2011, Red Hat, Inc + * All rights reserved. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * 1. Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * 2. Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution. + * 3. Neither the name of IBM nor the names of its contributors + * may be used to endorse or promote products derived from this software + * without specific prior written permission. + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS IS'' AND + * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE + * ARE DISCLAIMED. IN NO EVENT SHALL IBM OR CONTRIBUTORS BE LIABLE + * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL + * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS + * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) + * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT + * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY + * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF + * SUCH DAMAGE. + */ +#include <stdint.h> + +/* 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 the buffer contains a list of buffer descriptors. */ +#define VRING_DESC_F_INDIRECT 4 + +/* The Host uses this in used->flags to advise the Guest: don't kick me + * when you add a buffer. It's unreliable, so it's simply an + * optimization. Guest will still kick if it's out of buffers. */ +#define VRING_USED_F_NO_NOTIFY 1 +/* The Guest uses this in avail->flags to advise the Host: don't + * interrupt me when you consume a buffer. It's unreliable, so it's + * simply an optimization. */ +#define VRING_AVAIL_F_NO_INTERRUPT 1 + +/* Support for indirect descriptors */ +#define VIRTIO_RING_F_INDIRECT_DESC 28 + +/* Support for avail_idx and used_idx fields */ +#define VIRTIO_RING_F_EVENT_IDX 29 + +/* Arbitrary descriptor layouts. */ +#define VIRTIO_F_ANY_LAYOUT 27 + +/* Virtio ring descriptors: 16 bytes. + * These can chain together via "next". */ +struct vring_desc { + /* Address (guest-physical). */ + le64 addr; + /* Length. */ + le32 len; + /* The flags as indicated above. */ + le16 flags; + /* We chain unused descriptors via this, too */ + le16 next; +}; + +struct vring_avail { + le16 flags; + le16 idx; + le16 ring[]; + /* Only if VIRTIO_RING_F_EVENT_IDX: le16 used_event; */ +}; + +/* le32 is used here for ids for padding reasons. */ +struct vring_used_elem { + /* Index of start of used descriptor chain. */ + le32 id; + /* Total length of the descriptor chain which was written to. */ + le32 len; +}; + +struct vring_used { + le16 flags; + le16 idx; + struct vring_used_elem ring[]; + /* Only if VIRTIO_RING_F_EVENT_IDX: le16 avail_event; */ +}; + +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. 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. + * le16 avail_flags; + * le16 avail_idx; + * le16 available[num]; + * le16 used_event_idx; // Only if VIRTIO_RING_F_EVENT_IDX + * + * // Padding to the next align boundary. + * char pad[]; + * + * // A ring of used descriptor heads with free-running index. + * le16 used_flags; + * le16 used_idx; + * struct vring_used_elem used[num]; + * le16 avail_event_idx; // Only if VIRTIO_RING_F_EVENT_IDX + * }; + * Note: for virtio PCI, align is 4096. + */ +static inline void vring_init(struct vring *vr, unsigned int num, void *p, + unsigned long align) +{ + vr->num = num; + vr->desc = p; + vr->avail = p + num*sizeof(struct vring_desc); + vr->used = (void *)(((unsigned long)&vr->avail->ring[num] + sizeof(le16) + + align-1) + & ~(align - 1)); +} + +static inline unsigned vring_size(unsigned int num, unsigned long align) +{ + return ((sizeof(struct vring_desc)*num + sizeof(le16)*(3+num) + + align - 1) & ~(align - 1)) + + sizeof(le16)*3 + sizeof(struct vring_used_elem)*num; +} + +static inline int vring_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old_idx) +{ + return (uint16_t)(new_idx - event_idx - 1) < (uint16_t)(new_idx - old_idx); +} + +/* Get location of event indices (only with VIRTIO_RING_F_EVENT_IDX) */ +static inline le16 *vring_used_event(struct vring *vr) +{ + /* For backwards compat, used event index is at *end* of avail ring. */ + return &vr->avail->ring[vr->num]; +} + +static inline le16 *vring_avail_event(struct vring *vr) +{ + /* For backwards compat, avail event index is at *end* of used ring. */ + return (le16 *)&vr->used->ring[vr->num]; +} +#endif /* VIRTIO_RING_H */ |