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Annotation of qemu/linux-headers/linux/virtio_ring.h, revision 1.1

1.1     ! root        1: #ifndef _LINUX_VIRTIO_RING_H
        !             2: #define _LINUX_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 <linux/types.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:        /* Address (guest-physical). */
        !            64:        __u64 addr;
        !            65:        /* Length. */
        !            66:        __u32 len;
        !            67:        /* The flags as indicated above. */
        !            68:        __u16 flags;
        !            69:        /* We chain unused descriptors via this, too */
        !            70:        __u16 next;
        !            71: };
        !            72: 
        !            73: struct vring_avail {
        !            74:        __u16 flags;
        !            75:        __u16 idx;
        !            76:        __u16 ring[];
        !            77: };
        !            78: 
        !            79: /* u32 is used here for ids for padding reasons. */
        !            80: struct vring_used_elem {
        !            81:        /* Index of start of used descriptor chain. */
        !            82:        __u32 id;
        !            83:        /* Total length of the descriptor chain which was used (written to) */
        !            84:        __u32 len;
        !            85: };
        !            86: 
        !            87: struct vring_used {
        !            88:        __u16 flags;
        !            89:        __u16 idx;
        !            90:        struct vring_used_elem ring[];
        !            91: };
        !            92: 
        !            93: struct vring {
        !            94:        unsigned int num;
        !            95: 
        !            96:        struct vring_desc *desc;
        !            97: 
        !            98:        struct vring_avail *avail;
        !            99: 
        !           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] + align-1)
        !           139:                            & ~(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) * (2 + 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 */

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