Virtio helper routines for a descriptor ringbuffer implementation
These helper routines supply most of the virtqueue_ops for hypervisors which want to use a ring for virtio. Unlike the previous lguest implementation: 1) The rings are variable sized (2^n-1 elements). 2) They have an unfortunate limit of 65535 bytes per sg element. 3) The page numbers are always 64 bit (PAE anyone?) 4) They no longer place used[] on a separate page, just a separate cacheline. 5) We do a modulo on a variable. We could be tricky if we cared. 6) Interrupts and notifies are suppressed using flags within the rings. Users need only get the ring pages and provide a notify hook (KVM wants the guest to allocate the rings, lguest does it sanely). Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> Cc: Dor Laor <dor.laor@qumranet.com>
This commit is contained in:
Rusty Russell
313
drivers/virtio/virtio_ring.c
Normal file
313
drivers/virtio/virtio_ring.c
Normal file
@ -0,0 +1,313 @@
|
||||
/* Virtio ring implementation.
|
||||
*
|
||||
* Copyright 2007 Rusty Russell IBM Corporation
|
||||
*
|
||||
* 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
|
||||
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
||||
* 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., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
|
||||
*/
|
||||
#include <linux/virtio.h>
|
||||
#include <linux/virtio_ring.h>
|
||||
#include <linux/device.h>
|
||||
|
||||
#ifdef DEBUG
|
||||
/* For development, we want to crash whenever the ring is screwed. */
|
||||
#define BAD_RING(vq, fmt...) \
|
||||
do { dev_err(&vq->vq.vdev->dev, fmt); BUG(); } while(0)
|
||||
#define START_USE(vq) \
|
||||
do { if ((vq)->in_use) panic("in_use = %i\n", (vq)->in_use); (vq)->in_use = __LINE__; mb(); } while(0)
|
||||
#define END_USE(vq) \
|
||||
do { BUG_ON(!(vq)->in_use); (vq)->in_use = 0; mb(); } while(0)
|
||||
#else
|
||||
#define BAD_RING(vq, fmt...) \
|
||||
do { dev_err(&vq->vq.vdev->dev, fmt); (vq)->broken = true; } while(0)
|
||||
#define START_USE(vq)
|
||||
#define END_USE(vq)
|
||||
#endif
|
||||
|
||||
struct vring_virtqueue
|
||||
{
|
||||
struct virtqueue vq;
|
||||
|
||||
/* Actual memory layout for this queue */
|
||||
struct vring vring;
|
||||
|
||||
/* Other side has made a mess, don't try any more. */
|
||||
bool broken;
|
||||
|
||||
/* Number of free buffers */
|
||||
unsigned int num_free;
|
||||
/* Head of free buffer list. */
|
||||
unsigned int free_head;
|
||||
/* Number we've added since last sync. */
|
||||
unsigned int num_added;
|
||||
|
||||
/* Last used index we've seen. */
|
||||
unsigned int last_used_idx;
|
||||
|
||||
/* How to notify other side. FIXME: commonalize hcalls! */
|
||||
void (*notify)(struct virtqueue *vq);
|
||||
|
||||
#ifdef DEBUG
|
||||
/* They're supposed to lock for us. */
|
||||
unsigned int in_use;
|
||||
#endif
|
||||
|
||||
/* Tokens for callbacks. */
|
||||
void *data[];
|
||||
};
|
||||
|
||||
#define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq)
|
||||
|
||||
static int vring_add_buf(struct virtqueue *_vq,
|
||||
struct scatterlist sg[],
|
||||
unsigned int out,
|
||||
unsigned int in,
|
||||
void *data)
|
||||
{
|
||||
struct vring_virtqueue *vq = to_vvq(_vq);
|
||||
unsigned int i, avail, head, uninitialized_var(prev);
|
||||
|
||||
BUG_ON(data == NULL);
|
||||
BUG_ON(out + in > vq->vring.num);
|
||||
BUG_ON(out + in == 0);
|
||||
|
||||
START_USE(vq);
|
||||
|
||||
if (vq->num_free < out + in) {
|
||||
pr_debug("Can't add buf len %i - avail = %i\n",
|
||||
out + in, vq->num_free);
|
||||
END_USE(vq);
|
||||
return -ENOSPC;
|
||||
}
|
||||
|
||||
/* We're about to use some buffers from the free list. */
|
||||
vq->num_free -= out + in;
|
||||
|
||||
head = vq->free_head;
|
||||
for (i = vq->free_head; out; i = vq->vring.desc[i].next, out--) {
|
||||
vq->vring.desc[i].flags = VRING_DESC_F_NEXT;
|
||||
vq->vring.desc[i].addr = (page_to_pfn(sg_page(sg))<<PAGE_SHIFT)
|
||||
+ sg->offset;
|
||||
vq->vring.desc[i].len = sg->length;
|
||||
prev = i;
|
||||
sg++;
|
||||
}
|
||||
for (; in; i = vq->vring.desc[i].next, in--) {
|
||||
vq->vring.desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
|
||||
vq->vring.desc[i].addr = (page_to_pfn(sg_page(sg))<<PAGE_SHIFT)
|
||||
+ sg->offset;
|
||||
vq->vring.desc[i].len = sg->length;
|
||||
prev = i;
|
||||
sg++;
|
||||
}
|
||||
/* Last one doesn't continue. */
|
||||
vq->vring.desc[prev].flags &= ~VRING_DESC_F_NEXT;
|
||||
|
||||
/* Update free pointer */
|
||||
vq->free_head = i;
|
||||
|
||||
/* Set token. */
|
||||
vq->data[head] = data;
|
||||
|
||||
/* Put entry in available array (but don't update avail->idx until they
|
||||
* do sync). FIXME: avoid modulus here? */
|
||||
avail = (vq->vring.avail->idx + vq->num_added++) % vq->vring.num;
|
||||
vq->vring.avail->ring[avail] = head;
|
||||
|
||||
pr_debug("Added buffer head %i to %p\n", head, vq);
|
||||
END_USE(vq);
|
||||
return 0;
|
||||
}
|
||||
|
||||
static void vring_kick(struct virtqueue *_vq)
|
||||
{
|
||||
struct vring_virtqueue *vq = to_vvq(_vq);
|
||||
START_USE(vq);
|
||||
/* Descriptors and available array need to be set before we expose the
|
||||
* new available array entries. */
|
||||
wmb();
|
||||
|
||||
vq->vring.avail->idx += vq->num_added;
|
||||
vq->num_added = 0;
|
||||
|
||||
/* Need to update avail index before checking if we should notify */
|
||||
mb();
|
||||
|
||||
if (!(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY))
|
||||
/* Prod other side to tell it about changes. */
|
||||
vq->notify(&vq->vq);
|
||||
|
||||
END_USE(vq);
|
||||
}
|
||||
|
||||
static void detach_buf(struct vring_virtqueue *vq, unsigned int head)
|
||||
{
|
||||
unsigned int i;
|
||||
|
||||
/* Clear data ptr. */
|
||||
vq->data[head] = NULL;
|
||||
|
||||
/* Put back on free list: find end */
|
||||
i = head;
|
||||
while (vq->vring.desc[i].flags & VRING_DESC_F_NEXT) {
|
||||
i = vq->vring.desc[i].next;
|
||||
vq->num_free++;
|
||||
}
|
||||
|
||||
vq->vring.desc[i].next = vq->free_head;
|
||||
vq->free_head = head;
|
||||
/* Plus final descriptor */
|
||||
vq->num_free++;
|
||||
}
|
||||
|
||||
/* FIXME: We need to tell other side about removal, to synchronize. */
|
||||
static void vring_shutdown(struct virtqueue *_vq)
|
||||
{
|
||||
struct vring_virtqueue *vq = to_vvq(_vq);
|
||||
unsigned int i;
|
||||
|
||||
for (i = 0; i < vq->vring.num; i++)
|
||||
detach_buf(vq, i);
|
||||
}
|
||||
|
||||
static inline bool more_used(const struct vring_virtqueue *vq)
|
||||
{
|
||||
return vq->last_used_idx != vq->vring.used->idx;
|
||||
}
|
||||
|
||||
static void *vring_get_buf(struct virtqueue *_vq, unsigned int *len)
|
||||
{
|
||||
struct vring_virtqueue *vq = to_vvq(_vq);
|
||||
void *ret;
|
||||
unsigned int i;
|
||||
|
||||
START_USE(vq);
|
||||
|
||||
if (!more_used(vq)) {
|
||||
pr_debug("No more buffers in queue\n");
|
||||
END_USE(vq);
|
||||
return NULL;
|
||||
}
|
||||
|
||||
i = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].id;
|
||||
*len = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].len;
|
||||
|
||||
if (unlikely(i >= vq->vring.num)) {
|
||||
BAD_RING(vq, "id %u out of range\n", i);
|
||||
return NULL;
|
||||
}
|
||||
if (unlikely(!vq->data[i])) {
|
||||
BAD_RING(vq, "id %u is not a head!\n", i);
|
||||
return NULL;
|
||||
}
|
||||
|
||||
/* detach_buf clears data, so grab it now. */
|
||||
ret = vq->data[i];
|
||||
detach_buf(vq, i);
|
||||
vq->last_used_idx++;
|
||||
END_USE(vq);
|
||||
return ret;
|
||||
}
|
||||
|
||||
static bool vring_restart(struct virtqueue *_vq)
|
||||
{
|
||||
struct vring_virtqueue *vq = to_vvq(_vq);
|
||||
|
||||
START_USE(vq);
|
||||
BUG_ON(!(vq->vring.avail->flags & VRING_AVAIL_F_NO_INTERRUPT));
|
||||
|
||||
/* We optimistically turn back on interrupts, then check if there was
|
||||
* more to do. */
|
||||
vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
|
||||
mb();
|
||||
if (unlikely(more_used(vq))) {
|
||||
vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
|
||||
END_USE(vq);
|
||||
return false;
|
||||
}
|
||||
|
||||
END_USE(vq);
|
||||
return true;
|
||||
}
|
||||
|
||||
irqreturn_t vring_interrupt(int irq, void *_vq)
|
||||
{
|
||||
struct vring_virtqueue *vq = to_vvq(_vq);
|
||||
|
||||
if (!more_used(vq)) {
|
||||
pr_debug("virtqueue interrupt with no work for %p\n", vq);
|
||||
return IRQ_NONE;
|
||||
}
|
||||
|
||||
if (unlikely(vq->broken))
|
||||
return IRQ_HANDLED;
|
||||
|
||||
pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback);
|
||||
if (vq->vq.callback && !vq->vq.callback(&vq->vq))
|
||||
vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
|
||||
|
||||
return IRQ_HANDLED;
|
||||
}
|
||||
|
||||
static struct virtqueue_ops vring_vq_ops = {
|
||||
.add_buf = vring_add_buf,
|
||||
.get_buf = vring_get_buf,
|
||||
.kick = vring_kick,
|
||||
.restart = vring_restart,
|
||||
.shutdown = vring_shutdown,
|
||||
};
|
||||
|
||||
struct virtqueue *vring_new_virtqueue(unsigned int num,
|
||||
struct virtio_device *vdev,
|
||||
void *pages,
|
||||
void (*notify)(struct virtqueue *),
|
||||
bool (*callback)(struct virtqueue *))
|
||||
{
|
||||
struct vring_virtqueue *vq;
|
||||
unsigned int i;
|
||||
|
||||
vq = kmalloc(sizeof(*vq) + sizeof(void *)*num, GFP_KERNEL);
|
||||
if (!vq)
|
||||
return NULL;
|
||||
|
||||
vring_init(&vq->vring, num, pages);
|
||||
vq->vq.callback = callback;
|
||||
vq->vq.vdev = vdev;
|
||||
vq->vq.vq_ops = &vring_vq_ops;
|
||||
vq->notify = notify;
|
||||
vq->broken = false;
|
||||
vq->last_used_idx = 0;
|
||||
vq->num_added = 0;
|
||||
#ifdef DEBUG
|
||||
vq->in_use = false;
|
||||
#endif
|
||||
|
||||
/* No callback? Tell other side not to bother us. */
|
||||
if (!callback)
|
||||
vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
|
||||
|
||||
/* Put everything in free lists. */
|
||||
vq->num_free = num;
|
||||
vq->free_head = 0;
|
||||
for (i = 0; i < num-1; i++)
|
||||
vq->vring.desc[i].next = i+1;
|
||||
|
||||
return &vq->vq;
|
||||
}
|
||||
|
||||
void vring_del_virtqueue(struct virtqueue *vq)
|
||||
{
|
||||
kfree(to_vvq(vq));
|
||||
}
|
||||
|
||||
Reference in New Issue
Block a user