gem5  v21.1.0.2
virtio_ring.h
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1 #ifndef _VIRTIO_RING_H
2 #define _VIRTIO_RING_H
3 /* An interface for efficient virtio implementation, currently for use by KVM
4  * and lguest, but hopefully others soon. Do NOT change this since it will
5  * break existing servers and clients.
6  *
7  * This header is BSD licensed so anyone can use the definitions to implement
8  * compatible drivers/servers.
9  *
10  * Redistribution and use in source and binary forms, with or without
11  * modification, are permitted provided that the following conditions
12  * are met:
13  * 1. Redistributions of source code must retain the above copyright
14  * notice, this list of conditions and the following disclaimer.
15  * 2. Redistributions in binary form must reproduce the above copyright
16  * notice, this list of conditions and the following disclaimer in the
17  * documentation and/or other materials provided with the distribution.
18  * 3. Neither the name of IBM nor the names of its contributors
19  * may be used to endorse or promote products derived from this software
20  * without specific prior written permission.
21  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS IS'' AND
22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24  * ARE DISCLAIMED. IN NO EVENT SHALL IBM OR CONTRIBUTORS BE LIABLE
25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31  * SUCH DAMAGE.
32  *
33  * Copyright Rusty Russell IBM Corporation 2007. */
34 #include <stdint.h>
35 
36 /* This marks a buffer as continuing via the next field. */
37 #define VRING_DESC_F_NEXT 1
38 /* This marks a buffer as write-only (otherwise read-only). */
39 #define VRING_DESC_F_WRITE 2
40 /* This means the buffer contains a list of buffer descriptors. */
41 #define VRING_DESC_F_INDIRECT 4
42 
43 /* The Host uses this in used->flags to advise the Guest: don't kick me when
44  * you add a buffer. It's unreliable, so it's simply an optimization. Guest
45  * will still kick if it's out of buffers. */
46 #define VRING_USED_F_NO_NOTIFY 1
47 /* The Guest uses this in avail->flags to advise the Host: don't interrupt me
48  * when you consume a buffer. It's unreliable, so it's simply an
49  * optimization. */
50 #define VRING_AVAIL_F_NO_INTERRUPT 1
51 
52 /* We support indirect buffer descriptors */
53 #define VIRTIO_RING_F_INDIRECT_DESC 28
54 
55 /* The Guest publishes the used index for which it expects an interrupt
56  * at the end of the avail ring. Host should ignore the avail->flags field. */
57 /* The Host publishes the avail index for which it expects a kick
58  * at the end of the used ring. Guest should ignore the used->flags field. */
59 #define VIRTIO_RING_F_EVENT_IDX 29
60 
61 /* Virtio ring descriptors: 16 bytes. These can chain together via "next". */
62 struct vring_desc
63 {
64  /* Address (guest-physical). */
65  uint64_t addr;
66  /* Length. */
67  uint32_t len;
68  /* The flags as indicated above. */
69  uint16_t flags;
70  /* We chain unused descriptors via this, too */
71  uint16_t next;
72 };
73 
75 {
76  uint16_t flags;
77  uint16_t idx;
78  uint16_t ring[];
79 };
80 
81 /* u32 is used here for ids for padding reasons. */
83 {
84  /* Index of start of used descriptor chain. */
85  uint32_t id;
86  /* Total length of the descriptor chain which was used (written to) */
87  uint32_t len;
88 };
89 
90 struct vring_used
91 {
92  uint16_t flags;
93  uint16_t idx;
95 };
96 
97 struct vring
98 {
99  unsigned int num;
100 
101  struct vring_desc *desc;
102 
104 
105  struct vring_used *used;
106 };
107 
108 /* The standard layout for the ring is a continuous chunk of memory which looks
109  * like this. We assume num is a power of 2.
110  *
111  * struct vring
112  * {
113  * // The actual descriptors (16 bytes each)
114  * struct vring_desc desc[num];
115  *
116  * // A ring of available descriptor heads with free-running index.
117  * uint16_t avail_flags;
118  * uint16_t avail_idx;
119  * uint16_t available[num];
120  * uint16_t used_event_idx;
121  *
122  * // Padding to the next align boundary.
123  * char pad[];
124  *
125  * // A ring of used descriptor heads with free-running index.
126  * uint16_t used_flags;
127  * uint16_t used_idx;
128  * struct vring_used_elem used[num];
129  * uint16_t avail_event_idx;
130  * };
131  */
132 /* We publish the used event index at the end of the available ring, and vice
133  * versa. They are at the end for backwards compatibility. */
134 #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
135 #define vring_avail_event(vr) (*(uint16_t *)&(vr)->used->ring[(vr)->num])
136 
137 static inline void vring_init(struct vring *vr, unsigned int num, void *p,
138  unsigned long align)
139 {
140  vr->num = num;
141  vr->desc = (struct vring_desc *)p;
142  vr->avail = (struct vring_avail *)((uint8_t*)p + num*sizeof(struct vring_desc));
143  vr->used = (struct vring_used *)(((unsigned long)&vr->avail->ring[num] + sizeof(uint16_t)
144  + align-1) & ~(align - 1));
145 }
146 
147 static inline unsigned vring_size(unsigned int num, unsigned long align)
148 {
149  return ((sizeof(struct vring_desc) * num + sizeof(uint16_t) * (3 + num)
150  + align - 1) & ~(align - 1))
151  + sizeof(uint16_t) * 3 + sizeof(struct vring_used_elem) * num;
152 }
153 
154 /* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */
155 /* Assuming a given event_idx value from the other size, if
156  * we have just incremented index from old to new_idx,
157  * should we trigger an event? */
158 static inline int vring_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old)
159 {
160  /* Note: Xen has similar logic for notification hold-off
161  * in include/xen/interface/io/ring.h with req_event and req_prod
162  * corresponding to event_idx + 1 and new_idx respectively.
163  * Note also that req_event and req_prod in Xen start at 1,
164  * event indexes in virtio start at 0. */
165  return (uint16_t)(new_idx - event_idx - 1) < (uint16_t)(new_idx - old);
166 }
167 
168 #endif /* _VIRTIO_RING_H */
vring_need_event
static int vring_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old)
Definition: virtio_ring.h:158
vring_desc::addr
uint64_t addr
Definition: virtio_ring.h:65
vring_avail::flags
uint16_t flags
Definition: virtio_ring.h:76
vring_desc::len
uint32_t len
Definition: virtio_ring.h:67
vring::avail
struct vring_avail * avail
Definition: virtio_ring.h:103
vring_used
Definition: virtio_ring.h:90
vring_used_elem::id
uint32_t id
Definition: virtio_ring.h:85
sc_dt::align
void align(const scfx_rep &lhs, const scfx_rep &rhs, int &new_wp, int &len_mant, scfx_mant_ref &lhs_mant, scfx_mant_ref &rhs_mant)
Definition: scfx_rep.cc:2083
vring::used
struct vring_used * used
Definition: virtio_ring.h:105
vring_used::flags
uint16_t flags
Definition: virtio_ring.h:92
vring_size
static unsigned vring_size(unsigned int num, unsigned long align)
Definition: virtio_ring.h:147
gem5::MipsISA::p
Bitfield< 0 > p
Definition: pra_constants.hh:326
vring::desc
struct vring_desc * desc
Definition: virtio_ring.h:101
vring_avail
Definition: virtio_ring.h:74
vring_used::idx
uint16_t idx
Definition: virtio_ring.h:93
vring_used::ring
struct vring_used_elem ring[]
Definition: virtio_ring.h:94
vring_desc::next
uint16_t next
Definition: virtio_ring.h:71
vring_desc::flags
uint16_t flags
Definition: virtio_ring.h:69
vring_desc
Definition: virtio_ring.h:62
vring::num
unsigned int num
Definition: virtio_ring.h:99
vring_used_elem
Definition: virtio_ring.h:82
vring_init
static void vring_init(struct vring *vr, unsigned int num, void *p, unsigned long align)
Definition: virtio_ring.h:137
vring_used_elem::len
uint32_t len
Definition: virtio_ring.h:87
vring
Definition: virtio_ring.h:97
vring_avail::ring
uint16_t ring[]
Definition: virtio_ring.h:78
vring_avail::idx
uint16_t idx
Definition: virtio_ring.h:77

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