JezK
Edit File: virtio_ring.h
#ifndef _LINUX_VIRTIO_RING_H #define _LINUX_VIRTIO_RING_H /* An interface for efficient virtio implementation, currently for use by KVM, * 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 <stdint.h> #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 /* * Mark a descriptor as available or used in packed ring. * Notice: they are defined as shifts instead of shifted values. */ #define VRING_PACKED_DESC_F_AVAIL 7 #define VRING_PACKED_DESC_F_USED 15 /* 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 /* Enable events in packed ring. */ #define VRING_PACKED_EVENT_FLAG_ENABLE 0x0 /* Disable events in packed ring. */ #define VRING_PACKED_EVENT_FLAG_DISABLE 0x1 /* * Enable events for a specific descriptor in packed ring. * (as specified by Descriptor Ring Change Event Offset/Wrap Counter). * Only valid if VIRTIO_RING_F_EVENT_IDX has been negotiated. */ #define VRING_PACKED_EVENT_FLAG_DESC 0x2 /* * Wrap counter bit shift in event suppression structure * of packed ring. */ #define VRING_PACKED_EVENT_F_WRAP_CTR 15 /* 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 /* 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 /** * struct vring_desc - Virtio ring descriptors, * 16 bytes long. These can chain together via @next. * * @addr: buffer address (guest-physical) * @len: buffer length * @flags: descriptor flags * @next: index of the next descriptor in the chain, * if the VRING_DESC_F_NEXT flag is set. We chain unused * descriptors via this, too. */ struct vring_desc { __virtio64 addr; __virtio32 len; __virtio16 flags; __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; }; typedef struct vring_used_elem __attribute__((aligned(VRING_USED_ALIGN_SIZE))) vring_used_elem_t; struct vring_used { __virtio16 flags; __virtio16 idx; vring_used_elem_t ring[]; }; /* * The ring element addresses are passed between components with different * alignments assumptions. Thus, we might need to decrease the compiler-selected * alignment, and so must use a typedef to make sure the aligned attribute * actually takes hold: * * https://gcc.gnu.org/onlinedocs//gcc/Common-Type-Attributes.html#Common-Type-Attributes * * When used on a struct, or struct member, the aligned attribute can only * increase the alignment; in order to decrease it, the packed attribute must * be specified as well. When used as part of a typedef, the aligned attribute * can both increase and decrease alignment, and specifying the packed * attribute generates a warning. */ typedef struct vring_desc __attribute__((aligned(VRING_DESC_ALIGN_SIZE))) vring_desc_t; typedef struct vring_avail __attribute__((aligned(VRING_AVAIL_ALIGN_SIZE))) vring_avail_t; typedef struct vring_used __attribute__((aligned(VRING_USED_ALIGN_SIZE))) vring_used_t; struct vring { unsigned int num; vring_desc_t *desc; vring_avail_t *avail; vring_used_t *used; }; #ifndef VIRTIO_RING_NO_LEGACY /* 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 = (struct vring_avail *)((char *)p + num * sizeof(struct vring_desc)); vr->used = (void *)(((uintptr_t)&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; } #endif /* VIRTIO_RING_NO_LEGACY */ /* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */ /* Assuming a given event_idx value from the other side, 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); } struct vring_packed_desc_event { /* Descriptor Ring Change Event Offset/Wrap Counter. */ __le16 off_wrap; /* Descriptor Ring Change Event Flags. */ __le16 flags; }; struct vring_packed_desc { /* Buffer Address. */ __le64 addr; /* Buffer Length. */ __le32 len; /* Buffer ID. */ __le16 id; /* The flags depending on descriptor type. */ __le16 flags; }; #endif /* _LINUX_VIRTIO_RING_H */