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       1             : #ifndef _UAPI_LINUX_VIRTIO_RING_H
       2             : #define _UAPI_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'' 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             : #ifndef __KERNEL__
      35             : #include <stdint.h>
      36             : #endif
      37             : #include <linux/types.h>
      38             : #include <linux/virtio_types.h>
      39             : 
      40             : /* This marks a buffer as continuing via the next field. */
      41             : #define VRING_DESC_F_NEXT       1
      42             : /* This marks a buffer as write-only (otherwise read-only). */
      43             : #define VRING_DESC_F_WRITE      2
      44             : /* This means the buffer contains a list of buffer descriptors. */
      45             : #define VRING_DESC_F_INDIRECT   4
      46             : 
      47             : /*
      48             :  * Mark a descriptor as available or used in packed ring.
      49             :  * Notice: they are defined as shifts instead of shifted values.
      50             :  */
      51             : #define VRING_PACKED_DESC_F_AVAIL       7
      52             : #define VRING_PACKED_DESC_F_USED        15
      53             : 
      54             : /* The Host uses this in used->flags to advise the Guest: don't kick me when
      55             :  * you add a buffer.  It's unreliable, so it's simply an optimization.  Guest
      56             :  * will still kick if it's out of buffers. */
      57             : #define VRING_USED_F_NO_NOTIFY  1
      58             : /* The Guest uses this in avail->flags to advise the Host: don't interrupt me
      59             :  * when you consume a buffer.  It's unreliable, so it's simply an
      60             :  * optimization.  */
      61             : #define VRING_AVAIL_F_NO_INTERRUPT      1
      62             : 
      63             : /* Enable events in packed ring. */
      64             : #define VRING_PACKED_EVENT_FLAG_ENABLE  0x0
      65             : /* Disable events in packed ring. */
      66             : #define VRING_PACKED_EVENT_FLAG_DISABLE 0x1
      67             : /*
      68             :  * Enable events for a specific descriptor in packed ring.
      69             :  * (as specified by Descriptor Ring Change Event Offset/Wrap Counter).
      70             :  * Only valid if VIRTIO_RING_F_EVENT_IDX has been negotiated.
      71             :  */
      72             : #define VRING_PACKED_EVENT_FLAG_DESC    0x2
      73             : 
      74             : /*
      75             :  * Wrap counter bit shift in event suppression structure
      76             :  * of packed ring.
      77             :  */
      78             : #define VRING_PACKED_EVENT_F_WRAP_CTR   15
      79             : 
      80             : /* We support indirect buffer descriptors */
      81             : #define VIRTIO_RING_F_INDIRECT_DESC     28
      82             : 
      83             : /* The Guest publishes the used index for which it expects an interrupt
      84             :  * at the end of the avail ring. Host should ignore the avail->flags field. */
      85             : /* The Host publishes the avail index for which it expects a kick
      86             :  * at the end of the used ring. Guest should ignore the used->flags field. */
      87             : #define VIRTIO_RING_F_EVENT_IDX         29
      88             : 
      89             : /* Alignment requirements for vring elements.
      90             :  * When using pre-virtio 1.0 layout, these fall out naturally.
      91             :  */
      92             : #define VRING_AVAIL_ALIGN_SIZE 2
      93             : #define VRING_USED_ALIGN_SIZE 4
      94             : #define VRING_DESC_ALIGN_SIZE 16
      95             : 
      96             : /* Virtio ring descriptors: 16 bytes.  These can chain together via "next". */
      97             : struct vring_desc {
      98             :         /* Address (guest-physical). */
      99             :         __virtio64 addr;
     100             :         /* Length. */
     101             :         __virtio32 len;
     102             :         /* The flags as indicated above. */
     103             :         __virtio16 flags;
     104             :         /* We chain unused descriptors via this, too */
     105             :         __virtio16 next;
     106             : };
     107             : 
     108             : struct vring_avail {
     109             :         __virtio16 flags;
     110             :         __virtio16 idx;
     111             :         __virtio16 ring[];
     112             : };
     113             : 
     114             : /* u32 is used here for ids for padding reasons. */
     115             : struct vring_used_elem {
     116             :         /* Index of start of used descriptor chain. */
     117             :         __virtio32 id;
     118             :         /* Total length of the descriptor chain which was used (written to) */
     119             :         __virtio32 len;
     120             : };
     121             : 
     122             : typedef struct vring_used_elem __attribute__((aligned(VRING_USED_ALIGN_SIZE)))
     123             :         vring_used_elem_t;
     124             : 
     125             : struct vring_used {
     126             :         __virtio16 flags;
     127             :         __virtio16 idx;
     128             :         vring_used_elem_t ring[];
     129             : };
     130             : 
     131             : /*
     132             :  * The ring element addresses are passed between components with different
     133             :  * alignments assumptions. Thus, we might need to decrease the compiler-selected
     134             :  * alignment, and so must use a typedef to make sure the aligned attribute
     135             :  * actually takes hold:
     136             :  *
     137             :  * https://gcc.gnu.org/onlinedocs//gcc/Common-Type-Attributes.html#Common-Type-Attributes
     138             :  *
     139             :  * When used on a struct, or struct member, the aligned attribute can only
     140             :  * increase the alignment; in order to decrease it, the packed attribute must
     141             :  * be specified as well. When used as part of a typedef, the aligned attribute
     142             :  * can both increase and decrease alignment, and specifying the packed
     143             :  * attribute generates a warning.
     144             :  */
     145             : typedef struct vring_desc __attribute__((aligned(VRING_DESC_ALIGN_SIZE)))
     146             :         vring_desc_t;
     147             : typedef struct vring_avail __attribute__((aligned(VRING_AVAIL_ALIGN_SIZE)))
     148             :         vring_avail_t;
     149             : typedef struct vring_used __attribute__((aligned(VRING_USED_ALIGN_SIZE)))
     150             :         vring_used_t;
     151             : 
     152             : struct vring {
     153             :         unsigned int num;
     154             : 
     155             :         vring_desc_t *desc;
     156             : 
     157             :         vring_avail_t *avail;
     158             : 
     159             :         vring_used_t *used;
     160             : };
     161             : 
     162             : #ifndef VIRTIO_RING_NO_LEGACY
     163             : 
     164             : /* The standard layout for the ring is a continuous chunk of memory which looks
     165             :  * like this.  We assume num is a power of 2.
     166             :  *
     167             :  * struct vring
     168             :  * {
     169             :  *      // The actual descriptors (16 bytes each)
     170             :  *      struct vring_desc desc[num];
     171             :  *
     172             :  *      // A ring of available descriptor heads with free-running index.
     173             :  *      __virtio16 avail_flags;
     174             :  *      __virtio16 avail_idx;
     175             :  *      __virtio16 available[num];
     176             :  *      __virtio16 used_event_idx;
     177             :  *
     178             :  *      // Padding to the next align boundary.
     179             :  *      char pad[];
     180             :  *
     181             :  *      // A ring of used descriptor heads with free-running index.
     182             :  *      __virtio16 used_flags;
     183             :  *      __virtio16 used_idx;
     184             :  *      struct vring_used_elem used[num];
     185             :  *      __virtio16 avail_event_idx;
     186             :  * };
     187             :  */
     188             : /* We publish the used event index at the end of the available ring, and vice
     189             :  * versa. They are at the end for backwards compatibility. */
     190             : #define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
     191             : #define vring_avail_event(vr) (*(__virtio16 *)&(vr)->used->ring[(vr)->num])
     192             : 
     193           4 : static inline void vring_init(struct vring *vr, unsigned int num, void *p,
     194             :                               unsigned long align)
     195             : {
     196           4 :         vr->num = num;
     197           4 :         vr->desc = p;
     198           4 :         vr->avail = (struct vring_avail *)((char *)p + num * sizeof(struct vring_desc));
     199           4 :         vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16)
     200           4 :                 + align-1) & ~(align - 1));
     201             : }
     202             : 
     203           8 : static inline unsigned vring_size(unsigned int num, unsigned long align)
     204             : {
     205           8 :         return ((sizeof(struct vring_desc) * num + sizeof(__virtio16) * (3 + num)
     206           8 :                  + align - 1) & ~(align - 1))
     207           8 :                 + sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num;
     208             : }
     209             : 
     210             : #endif /* VIRTIO_RING_NO_LEGACY */
     211             : 
     212             : /* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */
     213             : /* Assuming a given event_idx value from the other side, if
     214             :  * we have just incremented index from old to new_idx,
     215             :  * should we trigger an event? */
     216        3214 : static inline int vring_need_event(__u16 event_idx, __u16 new_idx, __u16 old)
     217             : {
     218             :         /* Note: Xen has similar logic for notification hold-off
     219             :          * in include/xen/interface/io/ring.h with req_event and req_prod
     220             :          * corresponding to event_idx + 1 and new_idx respectively.
     221             :          * Note also that req_event and req_prod in Xen start at 1,
     222             :          * event indexes in virtio start at 0. */
     223        3214 :         return (__u16)(new_idx - event_idx - 1) < (__u16)(new_idx - old);
     224             : }
     225             : 
     226             : struct vring_packed_desc_event {
     227             :         /* Descriptor Ring Change Event Offset/Wrap Counter. */
     228             :         __le16 off_wrap;
     229             :         /* Descriptor Ring Change Event Flags. */
     230             :         __le16 flags;
     231             : };
     232             : 
     233             : struct vring_packed_desc {
     234             :         /* Buffer Address. */
     235             :         __le64 addr;
     236             :         /* Buffer Length. */
     237             :         __le32 len;
     238             :         /* Buffer ID. */
     239             :         __le16 id;
     240             :         /* The flags depending on descriptor type. */
     241             :         __le16 flags;
     242             : };
     243             : 
     244             : #endif /* _UAPI_LINUX_VIRTIO_RING_H */