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001: #ifndef _LINUX_VIRTIO_RING_H
002: #define _LINUX_VIRTIO_RING_H
003: /* An interface for efficient virtio implementation, currently for use by KVM
004:  * and lguest, but hopefully others soon.  Do NOT change this since it will
005:  * break existing servers and clients.
006:  *
007:  * This header is BSD licensed so anyone can use the definitions to implement
008:  * compatible drivers/servers.
009:  *
010:  * Redistribution and use in source and binary forms, with or without
011:  * modification, are permitted provided that the following conditions
012:  * are met:
013:  * 1. Redistributions of source code must retain the above copyright
014:  *    notice, this list of conditions and the following disclaimer.
015:  * 2. Redistributions in binary form must reproduce the above copyright
016:  *    notice, this list of conditions and the following disclaimer in the
017:  *    documentation and/or other materials provided with the distribution.
018:  * 3. Neither the name of IBM nor the names of its contributors
019:  *    may be used to endorse or promote products derived from this software
020:  *    without specific prior written permission.
021:  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS IS'' AND
022:  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
023:  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
024:  * ARE DISCLAIMED.  IN NO EVENT SHALL IBM OR CONTRIBUTORS BE LIABLE
025:  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
026:  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
027:  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
028:  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
029:  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
030:  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
031:  * SUCH DAMAGE.
032:  *
033:  * Copyright Rusty Russell IBM Corporation 2007. */
034: #include <linux/types.h>
035: 
036: /* This marks a buffer as continuing via the next field. */
037: #define VRING_DESC_F_NEXT       1
038: /* This marks a buffer as write-only (otherwise read-only). */
039: #define VRING_DESC_F_WRITE      2
040: /* This means the buffer contains a list of buffer descriptors. */
041: #define VRING_DESC_F_INDIRECT   4
042: 
043: /* The Host uses this in used->flags to advise the Guest: don't kick me when
044:  * you add a buffer.  It's unreliable, so it's simply an optimization.  Guest
045:  * will still kick if it's out of buffers. */
046: #define VRING_USED_F_NO_NOTIFY  1
047: /* The Guest uses this in avail->flags to advise the Host: don't interrupt me
048:  * when you consume a buffer.  It's unreliable, so it's simply an
049:  * optimization.  */
050: #define VRING_AVAIL_F_NO_INTERRUPT      1
051: 
052: /* We support indirect buffer descriptors */
053: #define VIRTIO_RING_F_INDIRECT_DESC     28
054: 
055: /* The Guest publishes the used index for which it expects an interrupt
056:  * at the end of the avail ring. Host should ignore the avail->flags field. */
057: /* The Host publishes the avail index for which it expects a kick
058:  * at the end of the used ring. Guest should ignore the used->flags field. */
059: #define VIRTIO_RING_F_EVENT_IDX         29
060: 
061: /* Virtio ring descriptors: 16 bytes.  These can chain together via "next". */
062: struct vring_desc {
063:         /* Address (guest-physical). */
064:         __u64 addr;
065:         /* Length. */
066:         __u32 len;
067:         /* The flags as indicated above. */
068:         __u16 flags;
069:         /* We chain unused descriptors via this, too */
070:         __u16 next;
071: };
072: 
073: struct vring_avail {
074:         __u16 flags;
075:         __u16 idx;
076:         __u16 ring[];
077: };
078: 
079: /* u32 is used here for ids for padding reasons. */
080: struct vring_used_elem {
081:         /* Index of start of used descriptor chain. */
082:         __u32 id;
083:         /* Total length of the descriptor chain which was used (written to) */
084:         __u32 len;
085: };
086: 
087: struct vring_used {
088:         __u16 flags;
089:         __u16 idx;
090:         struct vring_used_elem ring[];
091: };
092: 
093: struct vring {
094:         unsigned int num;
095: 
096:         struct vring_desc *desc;
097: 
098:         struct vring_avail *avail;
099: 
100:         struct vring_used *used;
101: };
102: 
103: /* The standard layout for the ring is a continuous chunk of memory which looks
104:  * like this.  We assume num is a power of 2.
105:  *
106:  * struct vring
107:  * {
108:  *      // The actual descriptors (16 bytes each)
109:  *      struct vring_desc desc[num];
110:  *
111:  *      // A ring of available descriptor heads with free-running index.
112:  *      __u16 avail_flags;
113:  *      __u16 avail_idx;
114:  *      __u16 available[num];
115:  *      __u16 used_event_idx;
116:  *
117:  *      // Padding to the next align boundary.
118:  *      char pad[];
119:  *
120:  *      // A ring of used descriptor heads with free-running index.
121:  *      __u16 used_flags;
122:  *      __u16 used_idx;
123:  *      struct vring_used_elem used[num];
124:  *      __u16 avail_event_idx;
125:  * };
126:  */
127: /* We publish the used event index at the end of the available ring, and vice
128:  * versa. They are at the end for backwards compatibility. */
129: #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
130: #define vring_avail_event(vr) (*(__u16 *)&(vr)->used->ring[(vr)->num])
131: 
132: static __inline__ void vring_init(struct vring *vr, unsigned int num, void *p,
133:                               unsigned long align)
134: {
135:         vr->num = num;
136:         vr->desc = p;
137:         vr->avail = p + num*sizeof(struct vring_desc);
138:         vr->used = (void *)(((unsigned long)&vr->avail->ring[num] + sizeof(__u16)
139:                 + align-1) & ~(align - 1));
140: }
141: 
142: static __inline__ unsigned vring_size(unsigned int num, unsigned long align)
143: {
144:         return ((sizeof(struct vring_desc) * num + sizeof(__u16) * (3 + num)
145:                  + align - 1) & ~(align - 1))
146:                 + sizeof(__u16) * 3 + sizeof(struct vring_used_elem) * num;
147: }
148: 
149: /* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */
150: /* Assuming a given event_idx value from the other size, if
151:  * we have just incremented index from old to new_idx,
152:  * should we trigger an event? */
153: static __inline__ int vring_need_event(__u16 event_idx, __u16 new_idx, __u16 old)
154: {
155:         /* Note: Xen has similar logic for notification hold-off
156:          * in include/xen/interface/io/ring.h with req_event and req_prod
157:          * corresponding to event_idx + 1 and new_idx respectively.
158:          * Note also that req_event and req_prod in Xen start at 1,
159:          * event indexes in virtio start at 0. */
160:         return (__u16)(new_idx - event_idx - 1) < (__u16)(new_idx - old);
161: }
162: 
163: #endif /* _LINUX_VIRTIO_RING_H */
164: 

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