Line data    Source code

       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             :  * 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
      22             : '' AND
      23             :  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
      24             :  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
      25             :  * ARE DISCLAIMED.  IN NO EVENT SHALL IBM OR CONTRIBUTORS BE LIABLE
      26             :  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
      27             :  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
      28             :  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
      29             :  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
      30             :  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
      31             :  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
      32             :  * SUCH DAMAGE.
      33             :  *
      34             :  * Copyright Rusty Russell IBM Corporation 2007. */
      35             : #ifndef __KERNEL__
      36             : #include <stdint.h>
      37             : #endif
      38             : #include <linux/types.h>
      39             : #include <linux/virtio_types.h>
      40             : 
      41             : /* This marks a buffer as continuing via the next field. */
      42             : #define VRING_DESC_F_NEXT       1
      43             : /* This marks a buffer as write-only (otherwise read-only). */
      44             : #define VRING_DESC_F_WRITE      2
      45             : /* This means the buffer contains a list of buffer descriptors. */
      46             : #define VRING_DESC_F_INDIRECT   4
      47             : 
      48             : /*
      49             :  * Mark a descriptor as available or used in packed ring.
      50             :  * Notice: they are defined as shifts instead of shifted values.
      51             :  */
      52             : #define VRING_PACKED_DESC_F_AVAIL       7
      53             : #define VRING_PACKED_DESC_F_USED        15
      54             : 
      55             : /* The Host uses this in used->flags to advise the Guest: don't kick me when
      56             :  * you add a buffer.  It's unreliable, so it's simply an optimization.  Guest
      57             :  * will still kick if it's out of buffers. */
      58             : #define VRING_USED_F_NO_NOTIFY  1
      59             : /* The Guest uses this in avail->flags to advise the Host: don't interrupt me
      60             :  * when you consume a buffer.  It's unreliable, so it's simply an
      61             :  * optimization.  */
      62             : #define VRING_AVAIL_F_NO_INTERRUPT      1
      63             : 
      64             : /* Enable events in packed ring. */
      65             : #define VRING_PACKED_EVENT_FLAG_ENABLE  0x0
      66             : /* Disable events in packed ring. */
      67             : #define VRING_PACKED_EVENT_FLAG_DISABLE 0x1
      68             : /*
      69             :  * Enable events for a specific descriptor in packed ring.
      70             :  * (as specified by Descriptor Ring Change Event Offset/Wrap Counter).
      71             :  * Only valid if VIRTIO_RING_F_EVENT_IDX has been negotiated.
      72             :  */
      73             : #define VRING_PACKED_EVENT_FLAG_DESC    0x2
      74             : 
      75             : /*
      76             :  * Wrap counter bit shift in event suppression structure
      77             :  * of packed ring.
      78             :  */
      79             : #define VRING_PACKED_EVENT_F_WRAP_CTR   15
      80             : 
      81             : /* We support indirect buffer descriptors */
      82             : #define VIRTIO_RING_F_INDIRECT_DESC     28
      83             : 
      84             : /* The Guest publishes the used index for which it expects an interrupt
      85             :  * at the end of the avail ring. Host should ignore the avail->flags field. */
      86             : /* The Host publishes the avail index for which it expects a kick
      87             :  * at the end of the used ring. Guest should ignore the used->flags field. */
      88             : #define VIRTIO_RING_F_EVENT_IDX         29
      89             : 
      90             : /* Virtio ring descriptors: 16 bytes.  These can chain together via "next". */
      91             : struct vring_desc {
      92             :         /* Address (guest-physical). */
      93             :         __virtio64 addr;
      94             :         /* Length. */
      95             :         __virtio32 len;
      96             :         /* The flags as indicated above. */
      97             :         __virtio16 flags;
      98             :         /* We chain unused descriptors via this, too */
      99             :         __virtio16 next;
     100             : };
     101             : 
     102             : struct vring_avail {
     103             :         __virtio16 flags;
     104             :         __virtio16 idx;
     105             :         __virtio16 ring[];
     106             : };
     107             : 
     108             : /* u32 is used here for ids for padding reasons. */
     109             : struct vring_used_elem {
     110             :         /* Index of start of used descriptor chain. */
     111             :         __virtio32 id;
     112             :         /* Total length of the descriptor chain which was used (written to) */
     113             :         __virtio32 len;
     114             : };
     115             : 
     116             : struct vring_used {
     117             :         __virtio16 flags;
     118             :         __virtio16 idx;
     119             :         struct vring_used_elem ring[];
     120             : };
     121             : 
     122             : struct vring {
     123             :         unsigned int num;
     124             : 
     125             :         struct vring_desc *desc;
     126             : 
     127             :         struct vring_avail *avail;
     128             : 
     129             :         struct vring_used *used;
     130             : };
     131             : 
     132             : /* Alignment requirements for vring elements.
     133             :  * When using pre-virtio 1.0 layout, these fall out naturally.
     134             :  */
     135             : #define VRING_AVAIL_ALIGN_SIZE 2
     136             : #define VRING_USED_ALIGN_SIZE 4
     137             : #define VRING_DESC_ALIGN_SIZE 16
     138             : 
     139             : /* The standard layout for the ring is a continuous chunk of memory which looks
     140             :  * like this.  We assume num is a power of 2.
     141             :  *
     142             :  * struct vring
     143             :  * {
     144             :  *       The actual descriptors (16 bytes each)
     145             :  *      struct vring_desc desc[num];
     146             :  *
     147             :  *       A ring of available descriptor heads with free-running index.
     148             :  *      __virtio16 avail_flags;
     149             :  *      __virtio16 avail_idx;
     150             :  *      __virtio16 available[num];
     151             :  *      __virtio16 used_event_idx;
     152             :  *
     153             :  *       Padding to the next align boundary.
     154             :  *      char pad[];
     155             :  *
     156             :  *       A ring of used descriptor heads with free-running index.
     157             :  *      __virtio16 used_flags;
     158             :  *      __virtio16 used_idx;
     159             :  *      struct vring_used_elem used[num];
     160             :  *      __virtio16 avail_event_idx;
     161             :  * };
     162             :  */
     163             : /* We publish the used event index at the end of the available ring, and vice
     164             :  * versa. They are at the end for backwards compatibility. */
     165             : #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
     166             : #define vring_avail_event(vr) (*(__virtio16 *)&(vr)->used->ring[(vr)->num])
     167             : 
     168             : static inline void
     169           0 : vring_init(struct vring *vr, unsigned int num, void *p,
     170             :            unsigned long align)
     171             : {
     172           0 :         vr->num = num;
     173           0 :         vr->desc = p;
     174           0 :         vr->avail = (struct vring_avail *)((char *)p + num * sizeof(struct vring_desc
     175             :                                                                    ));
     176           0 :         vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16)
     177           0 :                              + align - 1) & ~(align - 1));
     178           0 : }
     179             : 
     180             : static inline unsigned
     181           0 : vring_size(unsigned int num, unsigned long align)
     182             : {
     183           0 :         return ((sizeof(struct vring_desc) * num + sizeof(__virtio16) * (3 + num)
     184           0 :                  + align - 1) & ~(align - 1))
     185           0 :                + sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num;
     186             : }
     187             : 
     188             : /* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */
     189             : /* Assuming a given event_idx value from the other side, if
     190             :  * we have just incremented index from old to new_idx,
     191             :  * should we trigger an event? */
     192             : static inline int
     193           0 : vring_need_event(__u16 event_idx, __u16 new_idx, __u16 old)
     194             : {
     195             :         /* Note: Xen has similar logic for notification hold-off
     196             :          * in include/xen/interface/io/ring.h with req_event and req_prod
     197             :          * corresponding to event_idx + 1 and new_idx respectively.
     198             :          * Note also that req_event and req_prod in Xen start at 1,
     199             :          * event indexes in virtio start at 0. */
     200           0 :         return (__u16)(new_idx - event_idx - 1) < (__u16)(new_idx - old);
     201             : }
     202             : 
     203             : struct vring_packed_desc_event {
     204             :         /* Descriptor Ring Change Event Offset/Wrap Counter. */
     205             :         __le16 off_wrap;
     206             :         /* Descriptor Ring Change Event Flags. */
     207             :         __le16 flags;
     208             : };
     209             : 
     210             : struct vring_packed_desc {
     211             :         /* Buffer Address. */
     212             :         __le64 addr;
     213             :         /* Buffer Length. */
     214             :         __le32 len;
     215             :         /* Buffer ID. */
     216             :         __le16 id;
     217             :         /* The flags depending on descriptor type. */
     218             :         __le16 flags;
     219             : };
     220             : 
     221             : #endif /* _LINUX_VIRTIO_RING_H */