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TOMOYO Linux Cross Reference
Linux/include/uapi/linux/virtio_ring.h

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  1 #ifndef _UAPI_LINUX_VIRTIO_RING_H
  2 #define _UAPI_LINUX_VIRTIO_RING_H
  3 /* An interface for efficient virtio implementation, currently for use by KVM,
  4  * 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 #ifndef __KERNEL__
 35 #include <stdint.h>
 36 #endif
 37 #include <linux/types.h>
 38 #include <linux/virtio_types.h>
 39 
 40 /* This marks a buffer as continuing via the next field. */
 41 #define VRING_DESC_F_NEXT       1
 42 /* This marks a buffer as write-only (otherwise read-only). */
 43 #define VRING_DESC_F_WRITE      2
 44 /* This means the buffer contains a list of buffer descriptors. */
 45 #define VRING_DESC_F_INDIRECT   4
 46 
 47 /*
 48  * Mark a descriptor as available or used in packed ring.
 49  * Notice: they are defined as shifts instead of shifted values.
 50  */
 51 #define VRING_PACKED_DESC_F_AVAIL       7
 52 #define VRING_PACKED_DESC_F_USED        15
 53 
 54 /* The Host uses this in used->flags to advise the Guest: don't kick me when
 55  * you add a buffer.  It's unreliable, so it's simply an optimization.  Guest
 56  * will still kick if it's out of buffers. */
 57 #define VRING_USED_F_NO_NOTIFY  1
 58 /* The Guest uses this in avail->flags to advise the Host: don't interrupt me
 59  * when you consume a buffer.  It's unreliable, so it's simply an
 60  * optimization.  */
 61 #define VRING_AVAIL_F_NO_INTERRUPT      1
 62 
 63 /* Enable events in packed ring. */
 64 #define VRING_PACKED_EVENT_FLAG_ENABLE  0x0
 65 /* Disable events in packed ring. */
 66 #define VRING_PACKED_EVENT_FLAG_DISABLE 0x1
 67 /*
 68  * Enable events for a specific descriptor in packed ring.
 69  * (as specified by Descriptor Ring Change Event Offset/Wrap Counter).
 70  * Only valid if VIRTIO_RING_F_EVENT_IDX has been negotiated.
 71  */
 72 #define VRING_PACKED_EVENT_FLAG_DESC    0x2
 73 
 74 /*
 75  * Wrap counter bit shift in event suppression structure
 76  * of packed ring.
 77  */
 78 #define VRING_PACKED_EVENT_F_WRAP_CTR   15
 79 
 80 /* We support indirect buffer descriptors */
 81 #define VIRTIO_RING_F_INDIRECT_DESC     28
 82 
 83 /* The Guest publishes the used index for which it expects an interrupt
 84  * at the end of the avail ring. Host should ignore the avail->flags field. */
 85 /* The Host publishes the avail index for which it expects a kick
 86  * at the end of the used ring. Guest should ignore the used->flags field. */
 87 #define VIRTIO_RING_F_EVENT_IDX         29
 88 
 89 /* Virtio ring descriptors: 16 bytes.  These can chain together via "next". */
 90 struct vring_desc {
 91         /* Address (guest-physical). */
 92         __virtio64 addr;
 93         /* Length. */
 94         __virtio32 len;
 95         /* The flags as indicated above. */
 96         __virtio16 flags;
 97         /* We chain unused descriptors via this, too */
 98         __virtio16 next;
 99 };
100 
101 struct vring_avail {
102         __virtio16 flags;
103         __virtio16 idx;
104         __virtio16 ring[];
105 };
106 
107 /* u32 is used here for ids for padding reasons. */
108 struct vring_used_elem {
109         /* Index of start of used descriptor chain. */
110         __virtio32 id;
111         /* Total length of the descriptor chain which was used (written to) */
112         __virtio32 len;
113 };
114 
115 struct vring_used {
116         __virtio16 flags;
117         __virtio16 idx;
118         struct vring_used_elem ring[];
119 };
120 
121 struct vring {
122         unsigned int num;
123 
124         struct vring_desc *desc;
125 
126         struct vring_avail *avail;
127 
128         struct vring_used *used;
129 };
130 
131 /* Alignment requirements for vring elements.
132  * When using pre-virtio 1.0 layout, these fall out naturally.
133  */
134 #define VRING_AVAIL_ALIGN_SIZE 2
135 #define VRING_USED_ALIGN_SIZE 4
136 #define VRING_DESC_ALIGN_SIZE 16
137 
138 /* The standard layout for the ring is a continuous chunk of memory which looks
139  * like this.  We assume num is a power of 2.
140  *
141  * struct vring
142  * {
143  *      // The actual descriptors (16 bytes each)
144  *      struct vring_desc desc[num];
145  *
146  *      // A ring of available descriptor heads with free-running index.
147  *      __virtio16 avail_flags;
148  *      __virtio16 avail_idx;
149  *      __virtio16 available[num];
150  *      __virtio16 used_event_idx;
151  *
152  *      // Padding to the next align boundary.
153  *      char pad[];
154  *
155  *      // A ring of used descriptor heads with free-running index.
156  *      __virtio16 used_flags;
157  *      __virtio16 used_idx;
158  *      struct vring_used_elem used[num];
159  *      __virtio16 avail_event_idx;
160  * };
161  */
162 /* We publish the used event index at the end of the available ring, and vice
163  * versa. They are at the end for backwards compatibility. */
164 #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
165 #define vring_avail_event(vr) (*(__virtio16 *)&(vr)->used->ring[(vr)->num])
166 
167 static inline void vring_init(struct vring *vr, unsigned int num, void *p,
168                               unsigned long align)
169 {
170         vr->num = num;
171         vr->desc = p;
172         vr->avail = p + num*sizeof(struct vring_desc);
173         vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16)
174                 + align-1) & ~(align - 1));
175 }
176 
177 static inline unsigned vring_size(unsigned int num, unsigned long align)
178 {
179         return ((sizeof(struct vring_desc) * num + sizeof(__virtio16) * (3 + num)
180                  + align - 1) & ~(align - 1))
181                 + sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num;
182 }
183 
184 /* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */
185 /* Assuming a given event_idx value from the other side, if
186  * we have just incremented index from old to new_idx,
187  * should we trigger an event? */
188 static inline int vring_need_event(__u16 event_idx, __u16 new_idx, __u16 old)
189 {
190         /* Note: Xen has similar logic for notification hold-off
191          * in include/xen/interface/io/ring.h with req_event and req_prod
192          * corresponding to event_idx + 1 and new_idx respectively.
193          * Note also that req_event and req_prod in Xen start at 1,
194          * event indexes in virtio start at 0. */
195         return (__u16)(new_idx - event_idx - 1) < (__u16)(new_idx - old);
196 }
197 
198 struct vring_packed_desc_event {
199         /* Descriptor Ring Change Event Offset/Wrap Counter. */
200         __le16 off_wrap;
201         /* Descriptor Ring Change Event Flags. */
202         __le16 flags;
203 };
204 
205 struct vring_packed_desc {
206         /* Buffer Address. */
207         __le64 addr;
208         /* Buffer Length. */
209         __le32 len;
210         /* Buffer ID. */
211         __le16 id;
212         /* The flags depending on descriptor type. */
213         __le16 flags;
214 };
215 
216 #endif /* _UAPI_LINUX_VIRTIO_RING_H */
217 

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