#ifndef _LINUX_VIRTIO_RING_H
#define _LINUX_VIRTIO_RING_H
/* An interface for efficient virtio implementation, currently for use by KVM,
* 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.
*
* 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.
*
* Copyright Rusty Russell IBM Corporation 2007. */
#include <stdint.h>
#include "standard-headers/linux/types.h"
#include "standard-headers/linux/virtio_types.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
/*
* Mark a descriptor as available or used in packed ring.
* Notice: they are defined as shifts instead of shifted values.
*/
#define VRING_PACKED_DESC_F_AVAIL 7
#define VRING_PACKED_DESC_F_USED 15
/* 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
/* Enable events in packed ring. */
#define VRING_PACKED_EVENT_FLAG_ENABLE 0x0
/* Disable events in packed ring. */
#define VRING_PACKED_EVENT_FLAG_DISABLE 0x1
/*
* Enable events for a specific descriptor in packed ring.
* (as specified by Descriptor Ring Change Event Offset/Wrap Counter).
* Only valid if VIRTIO_RING_F_EVENT_IDX has been negotiated.
*/
#define VRING_PACKED_EVENT_FLAG_DESC 0x2
/*
* Wrap counter bit shift in event suppression structure
* of packed ring.
*/
#define VRING_PACKED_EVENT_F_WRAP_CTR 15
/* We support indirect buffer descriptors */
#define VIRTIO_RING_F_INDIRECT_DESC 28
/* The Guest publishes the used index for which it expects an interrupt
* at the end of the avail ring. Host should ignore the avail->flags field. */
/* The Host publishes the avail index for which it expects a kick
* at the end of the used ring. Guest should ignore the used->flags field. */
#define VIRTIO_RING_F_EVENT_IDX 29
/* 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
/* Virtio ring descriptors: 16 bytes. These can chain together via "next". */
struct vring_desc {
/* Address (guest-physical). */
__virtio64 addr;
/* Length. */
__virtio32 len;
/* The flags as indicated above. */
__virtio16 flags;
/* We chain unused descriptors via this, too */
__virtio16 next;
};
struct vring_avail {
__virtio16 flags;
__virtio16 idx;
__virtio16 ring[];
};
/* uint32_t is used here for ids for padding reasons. */
struct vring_used_elem {
/* Index of start of used descriptor chain. */
__virtio32 id;
/* Total length of the descriptor chain which was used (written to) */
__virtio32 len;
};
typedef struct vring_used_elem __attribute__((aligned(VRING_USED_ALIGN_SIZE)))
vring_used_elem_t;
struct vring_used {
__virtio16 flags;
__virtio16 idx;
vring_used_elem_t ring[];
};
/*
* The ring element addresses are passed between components with different
* alignments assumptions. Thus, we might need to decrease the compiler-selected
* alignment, and so must use a typedef to make sure the aligned attribute
* actually takes hold:
*
* https://gcc.gnu.org/onlinedocs//gcc/Common-Type-Attributes.html#Common-Type-Attributes
*
* When used on a struct, or struct member, the aligned attribute can only
* increase the alignment; in order to decrease it, the packed attribute must
* be specified as well. When used as part of a typedef, the aligned attribute
* can both increase and decrease alignment, and specifying the packed
* attribute generates a warning.
*/
typedef struct vring_desc __attribute__((aligned(VRING_DESC_ALIGN_SIZE)))
vring_desc_t;
typedef struct vring_avail __attribute__((aligned(VRING_AVAIL_ALIGN_SIZE)))
vring_avail_t;
typedef struct vring_used __attribute__((aligned(VRING_USED_ALIGN_SIZE)))
vring_used_t;
struct vring {
unsigned int num;
vring_desc_t *desc;
vring_avail_t *avail;
vring_used_t *used;
};
#ifndef VIRTIO_RING_NO_LEGACY
/* 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.
* __virtio16 avail_flags;
* __virtio16 avail_idx;
* __virtio16 available[num];
* __virtio16 used_event_idx;
*
* // Padding to the next align boundary.
* char pad[];
*
* // A ring of used descriptor heads with free-running index.
* __virtio16 used_flags;
* __virtio16 used_idx;
* struct vring_used_elem used[num];
* __virtio16 avail_event_idx;
* };
*/
/* We publish the used event index at the end of the available ring, and vice
* versa. They are at the end for backwards compatibility. */
#define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
#define vring_avail_event(vr) (*(__virtio16 *)&(vr)->used->ring[(vr)->num])
static inline void vring_init(struct vring *vr, unsigned int num, void *p,
unsigned long align)
{
vr->num = num;
vr->desc = p;
vr->avail = (struct vring_avail *)((char *)p + num * sizeof(struct vring_desc));
vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16)
+ align-1) & ~(align - 1));
}
static inline unsigned vring_size(unsigned int num, unsigned long align)
{
return ((sizeof(struct vring_desc) * num + sizeof(__virtio16) * (3 + num)
+ align - 1) & ~(align - 1))
+ sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num;
}
#endif /* VIRTIO_RING_NO_LEGACY */
/* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */
/* Assuming a given event_idx value from the other side, if
* we have just incremented index from old to new_idx,
* should we trigger an event? */
static inline int vring_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old)
{
/* Note: Xen has similar logic for notification hold-off
* in include/xen/interface/io/ring.h with req_event and req_prod
* corresponding to event_idx + 1 and new_idx respectively.
* Note also that req_event and req_prod in Xen start at 1,
* event indexes in virtio start at 0. */
return (uint16_t)(new_idx - event_idx - 1) < (uint16_t)(new_idx - old);
}
struct vring_packed_desc_event {
/* Descriptor Ring Change Event Offset/Wrap Counter. */
uint16_t off_wrap;
/* Descriptor Ring Change Event Flags. */
uint16_t flags;
};
struct vring_packed_desc {
/* Buffer Address. */
uint64_t addr;
/* Buffer Length. */
uint32_t len;
/* Buffer ID. */
uint16_t id;
/* The flags depending on descriptor type. */
uint16_t flags;
};
#endif /* _LINUX_VIRTIO_RING_H */
