Back to home page

OSCL-LXR

 
 

    


0001 #ifndef _UAPI_LINUX_VIRTIO_RING_H
0002 #define _UAPI_LINUX_VIRTIO_RING_H
0003 /* An interface for efficient virtio implementation, currently for use by KVM,
0004  * but hopefully others soon.  Do NOT change this since it will
0005  * break existing servers and clients.
0006  *
0007  * This header is BSD licensed so anyone can use the definitions to implement
0008  * compatible drivers/servers.
0009  *
0010  * Redistribution and use in source and binary forms, with or without
0011  * modification, are permitted provided that the following conditions
0012  * are met:
0013  * 1. Redistributions of source code must retain the above copyright
0014  *    notice, this list of conditions and the following disclaimer.
0015  * 2. Redistributions in binary form must reproduce the above copyright
0016  *    notice, this list of conditions and the following disclaimer in the
0017  *    documentation and/or other materials provided with the distribution.
0018  * 3. Neither the name of IBM nor the names of its contributors
0019  *    may be used to endorse or promote products derived from this software
0020  *    without specific prior written permission.
0021  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS IS'' AND
0022  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
0023  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
0024  * ARE DISCLAIMED.  IN NO EVENT SHALL IBM OR CONTRIBUTORS BE LIABLE
0025  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
0026  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
0027  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
0028  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
0029  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
0030  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
0031  * SUCH DAMAGE.
0032  *
0033  * Copyright Rusty Russell IBM Corporation 2007. */
0034 #ifndef __KERNEL__
0035 #include <stdint.h>
0036 #endif
0037 #include <linux/types.h>
0038 #include <linux/virtio_types.h>
0039 
0040 /* This marks a buffer as continuing via the next field. */
0041 #define VRING_DESC_F_NEXT   1
0042 /* This marks a buffer as write-only (otherwise read-only). */
0043 #define VRING_DESC_F_WRITE  2
0044 /* This means the buffer contains a list of buffer descriptors. */
0045 #define VRING_DESC_F_INDIRECT   4
0046 
0047 /*
0048  * Mark a descriptor as available or used in packed ring.
0049  * Notice: they are defined as shifts instead of shifted values.
0050  */
0051 #define VRING_PACKED_DESC_F_AVAIL   7
0052 #define VRING_PACKED_DESC_F_USED    15
0053 
0054 /* The Host uses this in used->flags to advise the Guest: don't kick me when
0055  * you add a buffer.  It's unreliable, so it's simply an optimization.  Guest
0056  * will still kick if it's out of buffers. */
0057 #define VRING_USED_F_NO_NOTIFY  1
0058 /* The Guest uses this in avail->flags to advise the Host: don't interrupt me
0059  * when you consume a buffer.  It's unreliable, so it's simply an
0060  * optimization.  */
0061 #define VRING_AVAIL_F_NO_INTERRUPT  1
0062 
0063 /* Enable events in packed ring. */
0064 #define VRING_PACKED_EVENT_FLAG_ENABLE  0x0
0065 /* Disable events in packed ring. */
0066 #define VRING_PACKED_EVENT_FLAG_DISABLE 0x1
0067 /*
0068  * Enable events for a specific descriptor in packed ring.
0069  * (as specified by Descriptor Ring Change Event Offset/Wrap Counter).
0070  * Only valid if VIRTIO_RING_F_EVENT_IDX has been negotiated.
0071  */
0072 #define VRING_PACKED_EVENT_FLAG_DESC    0x2
0073 
0074 /*
0075  * Wrap counter bit shift in event suppression structure
0076  * of packed ring.
0077  */
0078 #define VRING_PACKED_EVENT_F_WRAP_CTR   15
0079 
0080 /* We support indirect buffer descriptors */
0081 #define VIRTIO_RING_F_INDIRECT_DESC 28
0082 
0083 /* The Guest publishes the used index for which it expects an interrupt
0084  * at the end of the avail ring. Host should ignore the avail->flags field. */
0085 /* The Host publishes the avail index for which it expects a kick
0086  * at the end of the used ring. Guest should ignore the used->flags field. */
0087 #define VIRTIO_RING_F_EVENT_IDX     29
0088 
0089 /* Alignment requirements for vring elements.
0090  * When using pre-virtio 1.0 layout, these fall out naturally.
0091  */
0092 #define VRING_AVAIL_ALIGN_SIZE 2
0093 #define VRING_USED_ALIGN_SIZE 4
0094 #define VRING_DESC_ALIGN_SIZE 16
0095 
0096 /**
0097  * struct vring_desc - Virtio ring descriptors,
0098  * 16 bytes long. These can chain together via @next.
0099  *
0100  * @addr: buffer address (guest-physical)
0101  * @len: buffer length
0102  * @flags: descriptor flags
0103  * @next: index of the next descriptor in the chain,
0104  *        if the VRING_DESC_F_NEXT flag is set. We chain unused
0105  *        descriptors via this, too.
0106  */
0107 struct vring_desc {
0108     __virtio64 addr;
0109     __virtio32 len;
0110     __virtio16 flags;
0111     __virtio16 next;
0112 };
0113 
0114 struct vring_avail {
0115     __virtio16 flags;
0116     __virtio16 idx;
0117     __virtio16 ring[];
0118 };
0119 
0120 /* u32 is used here for ids for padding reasons. */
0121 struct vring_used_elem {
0122     /* Index of start of used descriptor chain. */
0123     __virtio32 id;
0124     /* Total length of the descriptor chain which was used (written to) */
0125     __virtio32 len;
0126 };
0127 
0128 typedef struct vring_used_elem __attribute__((aligned(VRING_USED_ALIGN_SIZE)))
0129     vring_used_elem_t;
0130 
0131 struct vring_used {
0132     __virtio16 flags;
0133     __virtio16 idx;
0134     vring_used_elem_t ring[];
0135 };
0136 
0137 /*
0138  * The ring element addresses are passed between components with different
0139  * alignments assumptions. Thus, we might need to decrease the compiler-selected
0140  * alignment, and so must use a typedef to make sure the aligned attribute
0141  * actually takes hold:
0142  *
0143  * https://gcc.gnu.org/onlinedocs//gcc/Common-Type-Attributes.html#Common-Type-Attributes
0144  *
0145  * When used on a struct, or struct member, the aligned attribute can only
0146  * increase the alignment; in order to decrease it, the packed attribute must
0147  * be specified as well. When used as part of a typedef, the aligned attribute
0148  * can both increase and decrease alignment, and specifying the packed
0149  * attribute generates a warning.
0150  */
0151 typedef struct vring_desc __attribute__((aligned(VRING_DESC_ALIGN_SIZE)))
0152     vring_desc_t;
0153 typedef struct vring_avail __attribute__((aligned(VRING_AVAIL_ALIGN_SIZE)))
0154     vring_avail_t;
0155 typedef struct vring_used __attribute__((aligned(VRING_USED_ALIGN_SIZE)))
0156     vring_used_t;
0157 
0158 struct vring {
0159     unsigned int num;
0160 
0161     vring_desc_t *desc;
0162 
0163     vring_avail_t *avail;
0164 
0165     vring_used_t *used;
0166 };
0167 
0168 #ifndef VIRTIO_RING_NO_LEGACY
0169 
0170 /* The standard layout for the ring is a continuous chunk of memory which looks
0171  * like this.  We assume num is a power of 2.
0172  *
0173  * struct vring
0174  * {
0175  *  // The actual descriptors (16 bytes each)
0176  *  struct vring_desc desc[num];
0177  *
0178  *  // A ring of available descriptor heads with free-running index.
0179  *  __virtio16 avail_flags;
0180  *  __virtio16 avail_idx;
0181  *  __virtio16 available[num];
0182  *  __virtio16 used_event_idx;
0183  *
0184  *  // Padding to the next align boundary.
0185  *  char pad[];
0186  *
0187  *  // A ring of used descriptor heads with free-running index.
0188  *  __virtio16 used_flags;
0189  *  __virtio16 used_idx;
0190  *  struct vring_used_elem used[num];
0191  *  __virtio16 avail_event_idx;
0192  * };
0193  */
0194 /* We publish the used event index at the end of the available ring, and vice
0195  * versa. They are at the end for backwards compatibility. */
0196 #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
0197 #define vring_avail_event(vr) (*(__virtio16 *)&(vr)->used->ring[(vr)->num])
0198 
0199 static inline void vring_init(struct vring *vr, unsigned int num, void *p,
0200                   unsigned long align)
0201 {
0202     vr->num = num;
0203     vr->desc = p;
0204     vr->avail = (struct vring_avail *)((char *)p + num * sizeof(struct vring_desc));
0205     vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16)
0206         + align-1) & ~(align - 1));
0207 }
0208 
0209 static inline unsigned vring_size(unsigned int num, unsigned long align)
0210 {
0211     return ((sizeof(struct vring_desc) * num + sizeof(__virtio16) * (3 + num)
0212          + align - 1) & ~(align - 1))
0213         + sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num;
0214 }
0215 
0216 #endif /* VIRTIO_RING_NO_LEGACY */
0217 
0218 /* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */
0219 /* Assuming a given event_idx value from the other side, if
0220  * we have just incremented index from old to new_idx,
0221  * should we trigger an event? */
0222 static inline int vring_need_event(__u16 event_idx, __u16 new_idx, __u16 old)
0223 {
0224     /* Note: Xen has similar logic for notification hold-off
0225      * in include/xen/interface/io/ring.h with req_event and req_prod
0226      * corresponding to event_idx + 1 and new_idx respectively.
0227      * Note also that req_event and req_prod in Xen start at 1,
0228      * event indexes in virtio start at 0. */
0229     return (__u16)(new_idx - event_idx - 1) < (__u16)(new_idx - old);
0230 }
0231 
0232 struct vring_packed_desc_event {
0233     /* Descriptor Ring Change Event Offset/Wrap Counter. */
0234     __le16 off_wrap;
0235     /* Descriptor Ring Change Event Flags. */
0236     __le16 flags;
0237 };
0238 
0239 struct vring_packed_desc {
0240     /* Buffer Address. */
0241     __le64 addr;
0242     /* Buffer Length. */
0243     __le32 len;
0244     /* Buffer ID. */
0245     __le16 id;
0246     /* The flags depending on descriptor type. */
0247     __le16 flags;
0248 };
0249 
0250 #endif /* _UAPI_LINUX_VIRTIO_RING_H */