243 lines
8.4 KiB
C
243 lines
8.4 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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* 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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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of IBM nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL IBM OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* Copyright Rusty Russell IBM Corporation 2007. */
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#include <stdint.h>
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#include "standard-headers/linux/types.h"
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#include "standard-headers/linux/virtio_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 the buffer contains a list of buffer descriptors. */
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#define VRING_DESC_F_INDIRECT 4
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/*
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* Mark a descriptor as available or used in packed ring.
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* Notice: they are defined as shifts instead of shifted values.
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*/
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#define VRING_PACKED_DESC_F_AVAIL 7
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#define VRING_PACKED_DESC_F_USED 15
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/* The Host uses this in used->flags to advise the Guest: don't kick me when
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* you add a buffer. It's unreliable, so it's simply an optimization. Guest
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* will still kick if it's out of buffers. */
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#define VRING_USED_F_NO_NOTIFY 1
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/* The Guest uses this in avail->flags to advise the Host: don't interrupt me
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* when you consume a buffer. It's unreliable, so it's simply an
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* optimization. */
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#define VRING_AVAIL_F_NO_INTERRUPT 1
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/* Enable events in packed ring. */
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#define VRING_PACKED_EVENT_FLAG_ENABLE 0x0
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/* Disable events in packed ring. */
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#define VRING_PACKED_EVENT_FLAG_DISABLE 0x1
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/*
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* Enable events for a specific descriptor in packed ring.
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* (as specified by Descriptor Ring Change Event Offset/Wrap Counter).
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* Only valid if VIRTIO_RING_F_EVENT_IDX has been negotiated.
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*/
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#define VRING_PACKED_EVENT_FLAG_DESC 0x2
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/*
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* Wrap counter bit shift in event suppression structure
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* of packed ring.
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*/
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#define VRING_PACKED_EVENT_F_WRAP_CTR 15
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/* We support indirect buffer descriptors */
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#define VIRTIO_RING_F_INDIRECT_DESC 28
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/* The Guest publishes the used index for which it expects an interrupt
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* at the end of the avail ring. Host should ignore the avail->flags field. */
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/* The Host publishes the avail index for which it expects a kick
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* at the end of the used ring. Guest should ignore the used->flags field. */
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#define VIRTIO_RING_F_EVENT_IDX 29
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/* Alignment requirements for vring elements.
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* When using pre-virtio 1.0 layout, these fall out naturally.
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*/
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#define VRING_AVAIL_ALIGN_SIZE 2
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#define VRING_USED_ALIGN_SIZE 4
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#define VRING_DESC_ALIGN_SIZE 16
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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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/* Address (guest-physical). */
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__virtio64 addr;
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/* Length. */
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__virtio32 len;
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/* The flags as indicated above. */
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__virtio16 flags;
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/* We chain unused descriptors via this, too */
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__virtio16 next;
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};
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struct vring_avail {
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__virtio16 flags;
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__virtio16 idx;
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__virtio16 ring[];
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};
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/* uint32_t is used here for ids for padding reasons. */
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struct vring_used_elem {
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/* Index of start of used descriptor chain. */
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__virtio32 id;
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/* Total length of the descriptor chain which was used (written to) */
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__virtio32 len;
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};
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typedef struct vring_used_elem __attribute__((aligned(VRING_USED_ALIGN_SIZE)))
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vring_used_elem_t;
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struct vring_used {
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__virtio16 flags;
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__virtio16 idx;
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vring_used_elem_t ring[];
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};
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/*
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* The ring element addresses are passed between components with different
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* alignments assumptions. Thus, we might need to decrease the compiler-selected
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* alignment, and so must use a typedef to make sure the aligned attribute
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* actually takes hold:
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*
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* https://gcc.gnu.org/onlinedocs//gcc/Common-Type-Attributes.html#Common-Type-Attributes
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*
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* When used on a struct, or struct member, the aligned attribute can only
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* increase the alignment; in order to decrease it, the packed attribute must
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* be specified as well. When used as part of a typedef, the aligned attribute
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* can both increase and decrease alignment, and specifying the packed
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* attribute generates a warning.
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*/
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typedef struct vring_desc __attribute__((aligned(VRING_DESC_ALIGN_SIZE)))
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vring_desc_t;
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typedef struct vring_avail __attribute__((aligned(VRING_AVAIL_ALIGN_SIZE)))
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vring_avail_t;
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typedef struct vring_used __attribute__((aligned(VRING_USED_ALIGN_SIZE)))
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vring_used_t;
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struct vring {
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unsigned int num;
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vring_desc_t *desc;
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vring_avail_t *avail;
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vring_used_t *used;
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};
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#ifndef VIRTIO_RING_NO_LEGACY
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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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* __virtio16 avail_flags;
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* __virtio16 avail_idx;
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* __virtio16 available[num];
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* __virtio16 used_event_idx;
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*
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* // Padding to the next align 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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* __virtio16 used_flags;
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* __virtio16 used_idx;
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* struct vring_used_elem used[num];
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* __virtio16 avail_event_idx;
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* };
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*/
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/* We publish the used event index at the end of the available ring, and vice
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* versa. They are at the end for backwards compatibility. */
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#define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
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#define vring_avail_event(vr) (*(__virtio16 *)&(vr)->used->ring[(vr)->num])
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static inline void vring_init(struct vring *vr, unsigned int num, void *p,
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unsigned long align)
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{
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vr->num = num;
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vr->desc = p;
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vr->avail = (struct vring_avail *)((char *)p + num * sizeof(struct vring_desc));
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vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16)
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+ align-1) & ~(align - 1));
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}
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static inline unsigned vring_size(unsigned int num, unsigned long align)
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{
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return ((sizeof(struct vring_desc) * num + sizeof(__virtio16) * (3 + num)
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+ align - 1) & ~(align - 1))
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+ sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num;
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}
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#endif /* VIRTIO_RING_NO_LEGACY */
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/* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */
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/* Assuming a given event_idx value from the other side, if
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* we have just incremented index from old to new_idx,
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* should we trigger an event? */
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static inline int vring_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old)
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{
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/* Note: Xen has similar logic for notification hold-off
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* in include/xen/interface/io/ring.h with req_event and req_prod
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* corresponding to event_idx + 1 and new_idx respectively.
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* Note also that req_event and req_prod in Xen start at 1,
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* event indexes in virtio start at 0. */
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return (uint16_t)(new_idx - event_idx - 1) < (uint16_t)(new_idx - old);
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}
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struct vring_packed_desc_event {
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/* Descriptor Ring Change Event Offset/Wrap Counter. */
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uint16_t off_wrap;
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/* Descriptor Ring Change Event Flags. */
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uint16_t flags;
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};
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struct vring_packed_desc {
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/* Buffer Address. */
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uint64_t addr;
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/* Buffer Length. */
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uint32_t len;
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/* Buffer ID. */
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uint16_t id;
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/* The flags depending on descriptor type. */
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uint16_t flags;
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};
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#endif /* _LINUX_VIRTIO_RING_H */
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