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Current File : //usr/include/linux/virtio_ring.h
#ifndef _LINUX_VIRTIO_RING_H #define _LINUX_VIRTIO_RING_H /* An interface for efficient virtio implementation, currently for use by KVM * and lguest, but hopefully others soon. Do NOT change this since it will * break existing servers and clients. * * This header is BSD licensed so anyone can use the definitions to implement * compatible drivers/servers. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * 3. Neither the name of IBM nor the names of its contributors * may be used to endorse or promote products derived from this software * without specific prior written permission. * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS IS'' AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL IBM OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. * * Copyright Rusty Russell IBM Corporation 2007. */ #include <linux/types.h> #include <linux/virtio_types.h> /* This marks a buffer as continuing via the next field. */ #define VRING_DESC_F_NEXT 1 /* This marks a buffer as write-only (otherwise read-only). */ #define VRING_DESC_F_WRITE 2 /* This means the buffer contains a list of buffer descriptors. */ #define VRING_DESC_F_INDIRECT 4 /* The Host uses this in used->flags to advise the Guest: don't kick me when * you add a buffer. It's unreliable, so it's simply an optimization. Guest * will still kick if it's out of buffers. */ #define VRING_USED_F_NO_NOTIFY 1 /* The Guest uses this in avail->flags to advise the Host: don't interrupt me * when you consume a buffer. It's unreliable, so it's simply an * optimization. */ #define VRING_AVAIL_F_NO_INTERRUPT 1 /* We support indirect buffer descriptors */ #define VIRTIO_RING_F_INDIRECT_DESC 28 /* The Guest publishes the used index for which it expects an interrupt * at the end of the avail ring. Host should ignore the avail->flags field. */ /* The Host publishes the avail index for which it expects a kick * at the end of the used ring. Guest should ignore the used->flags field. */ #define VIRTIO_RING_F_EVENT_IDX 29 /* Virtio ring descriptors: 16 bytes. These can chain together via "next". */ struct vring_desc { /* Address (guest-physical). */ __virtio64 addr; /* Length. */ __virtio32 len; /* The flags as indicated above. */ __virtio16 flags; /* We chain unused descriptors via this, too */ __virtio16 next; }; struct vring_avail { __virtio16 flags; __virtio16 idx; __virtio16 ring[]; }; /* u32 is used here for ids for padding reasons. */ struct vring_used_elem { /* Index of start of used descriptor chain. */ __virtio32 id; /* Total length of the descriptor chain which was used (written to) */ __virtio32 len; }; struct vring_used { __virtio16 flags; __virtio16 idx; struct vring_used_elem ring[]; }; struct vring { unsigned int num; struct vring_desc *desc; struct vring_avail *avail; struct vring_used *used; }; /* Alignment requirements for vring elements. * When using pre-virtio 1.0 layout, these fall out naturally. */ #define VRING_AVAIL_ALIGN_SIZE 2 #define VRING_USED_ALIGN_SIZE 4 #define VRING_DESC_ALIGN_SIZE 16 /* The standard layout for the ring is a continuous chunk of memory which looks * like this. We assume num is a power of 2. * * struct vring * { * // The actual descriptors (16 bytes each) * struct vring_desc desc[num]; * * // A ring of available descriptor heads with free-running index. * __virtio16 avail_flags; * __virtio16 avail_idx; * __virtio16 available[num]; * __virtio16 used_event_idx; * * // Padding to the next align boundary. * char pad[]; * * // A ring of used descriptor heads with free-running index. * __virtio16 used_flags; * __virtio16 used_idx; * struct vring_used_elem used[num]; * __virtio16 avail_event_idx; * }; */ /* We publish the used event index at the end of the available ring, and vice * versa. They are at the end for backwards compatibility. */ #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num]) #define vring_avail_event(vr) (*(__virtio16 *)&(vr)->used->ring[(vr)->num]) static __inline__ void vring_init(struct vring *vr, unsigned int num, void *p, unsigned long align) { vr->num = num; vr->desc = p; vr->avail = p + num*sizeof(struct vring_desc); vr->used = (void *)(((unsigned long)&vr->avail->ring[num] + sizeof(__virtio16) + align-1) & ~(align - 1)); } static __inline__ unsigned vring_size(unsigned int num, unsigned long align) { return ((sizeof(struct vring_desc) * num + sizeof(__virtio16) * (3 + num) + align - 1) & ~(align - 1)) + sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num; } /* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */ /* Assuming a given event_idx value from the other size, if * we have just incremented index from old to new_idx, * should we trigger an event? */ static __inline__ int vring_need_event(__u16 event_idx, __u16 new_idx, __u16 old) { /* Note: Xen has similar logic for notification hold-off * in include/xen/interface/io/ring.h with req_event and req_prod * corresponding to event_idx + 1 and new_idx respectively. * Note also that req_event and req_prod in Xen start at 1, * event indexes in virtio start at 0. */ return (__u16)(new_idx - event_idx - 1) < (__u16)(new_idx - old); } #endif /* _LINUX_VIRTIO_RING_H */
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