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* Linux host-side vring helpers; for when the kernel needs to access
* someone else's vring.
* Copyright IBM Corporation, 2013.
* Parts taken from drivers/vhost/vhost.c Copyright 2009 Red Hat, Inc.
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* GNU General Public License for more details.
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
* Written by: Rusty Russell <>
#include <uapi/linux/virtio_ring.h>
#include <linux/uio.h>
#include <linux/slab.h>
#include <asm/barrier.h>
/* virtio_ring with information needed for host access. */
struct vringh {
/* Guest publishes used event idx (note: we always do). */
bool event_indices;
/* Can we get away with weak barriers? */
bool weak_barriers;
/* Last available index we saw (ie. where we're up to). */
u16 last_avail_idx;
/* Last index we used. */
u16 last_used_idx;
/* How many descriptors we've completed since last need_notify(). */
u32 completed;
/* The vring (note: it may contain user pointers!) */
struct vring vring;
/* The function to call to notify the guest about added buffers */
void (*notify)(struct vringh *);
* struct vringh_config_ops - ops for creating a host vring from a virtio driver
* @find_vrhs: find the host vrings and instantiate them
* vdev: the virtio_device
* nhvrs: the number of host vrings to find
* hvrs: on success, includes new host vrings
* callbacks: array of driver callbacks, for each host vring
* include a NULL entry for vqs that do not need a callback
* Returns 0 on success or error status
* @del_vrhs: free the host vrings found by find_vrhs().
struct virtio_device;
typedef void vrh_callback_t(struct virtio_device *, struct vringh *);
struct vringh_config_ops {
int (*find_vrhs)(struct virtio_device *vdev, unsigned nhvrs,
struct vringh *vrhs[], vrh_callback_t *callbacks[]);
void (*del_vrhs)(struct virtio_device *vdev);
/* The memory the vring can access, and what offset to apply. */
struct vringh_range {
u64 start, end_incl;
u64 offset;
* struct vringh_iov - iovec mangler.
* Mangles iovec in place, and restores it.
* Remaining data is iov + i, of used - i elements.
struct vringh_iov {
struct iovec *iov;
size_t consumed; /* Within iov[i] */
unsigned i, used, max_num;
* struct vringh_iov - kvec mangler.
* Mangles kvec in place, and restores it.
* Remaining data is iov + i, of used - i elements.
struct vringh_kiov {
struct kvec *iov;
size_t consumed; /* Within iov[i] */
unsigned i, used, max_num;
/* Flag on max_num to indicate we're kmalloced. */
#define VRINGH_IOV_ALLOCATED 0x8000000
/* Helpers for userspace vrings. */
int vringh_init_user(struct vringh *vrh, u32 features,
unsigned int num, bool weak_barriers,
struct vring_desc __user *desc,
struct vring_avail __user *avail,
struct vring_used __user *used);
static inline void vringh_iov_init(struct vringh_iov *iov,
struct iovec *iovec, unsigned num)
iov->used = iov->i = 0;
iov->consumed = 0;
iov->max_num = num;
iov->iov = iovec;
static inline void vringh_iov_reset(struct vringh_iov *iov)
iov->iov[iov->i].iov_len += iov->consumed;
iov->iov[iov->i].iov_base -= iov->consumed;
iov->consumed = 0;
iov->i = 0;
static inline void vringh_iov_cleanup(struct vringh_iov *iov)
if (iov->max_num & VRINGH_IOV_ALLOCATED)
iov->max_num = iov->used = iov->i = iov->consumed = 0;
iov->iov = NULL;
/* Convert a descriptor into iovecs. */
int vringh_getdesc_user(struct vringh *vrh,
struct vringh_iov *riov,
struct vringh_iov *wiov,
bool (*getrange)(struct vringh *vrh,
u64 addr, struct vringh_range *r),
u16 *head);
/* Copy bytes from readable vsg, consuming it (and incrementing wiov->i). */
ssize_t vringh_iov_pull_user(struct vringh_iov *riov, void *dst, size_t len);
/* Copy bytes into writable vsg, consuming it (and incrementing wiov->i). */
ssize_t vringh_iov_push_user(struct vringh_iov *wiov,
const void *src, size_t len);
/* Mark a descriptor as used. */
int vringh_complete_user(struct vringh *vrh, u16 head, u32 len);
int vringh_complete_multi_user(struct vringh *vrh,
const struct vring_used_elem used[],
unsigned num_used);
/* Pretend we've never seen descriptor (for easy error handling). */
void vringh_abandon_user(struct vringh *vrh, unsigned int num);
/* Do we need to fire the eventfd to notify the other side? */
int vringh_need_notify_user(struct vringh *vrh);
bool vringh_notify_enable_user(struct vringh *vrh);
void vringh_notify_disable_user(struct vringh *vrh);
/* Helpers for kernelspace vrings. */
int vringh_init_kern(struct vringh *vrh, u32 features,
unsigned int num, bool weak_barriers,
struct vring_desc *desc,
struct vring_avail *avail,
struct vring_used *used);
static inline void vringh_kiov_init(struct vringh_kiov *kiov,
struct kvec *kvec, unsigned num)
kiov->used = kiov->i = 0;
kiov->consumed = 0;
kiov->max_num = num;
kiov->iov = kvec;
static inline void vringh_kiov_reset(struct vringh_kiov *kiov)
kiov->iov[kiov->i].iov_len += kiov->consumed;
kiov->iov[kiov->i].iov_base -= kiov->consumed;
kiov->consumed = 0;
kiov->i = 0;
static inline void vringh_kiov_cleanup(struct vringh_kiov *kiov)
if (kiov->max_num & VRINGH_IOV_ALLOCATED)
kiov->max_num = kiov->used = kiov->i = kiov->consumed = 0;
kiov->iov = NULL;
int vringh_getdesc_kern(struct vringh *vrh,
struct vringh_kiov *riov,
struct vringh_kiov *wiov,
u16 *head,
gfp_t gfp);
ssize_t vringh_iov_pull_kern(struct vringh_kiov *riov, void *dst, size_t len);
ssize_t vringh_iov_push_kern(struct vringh_kiov *wiov,
const void *src, size_t len);
void vringh_abandon_kern(struct vringh *vrh, unsigned int num);
int vringh_complete_kern(struct vringh *vrh, u16 head, u32 len);
bool vringh_notify_enable_kern(struct vringh *vrh);
void vringh_notify_disable_kern(struct vringh *vrh);
int vringh_need_notify_kern(struct vringh *vrh);
/* Notify the guest about buffers added to the used ring */
static inline void vringh_notify(struct vringh *vrh)
if (vrh->notify)
#endif /* _LINUX_VRINGH_H */