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lguest: wrap last_avail accesses.

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To simplify the transition to when we publish indices in the ring
(and make shuffling my patch queue easier), wrap them in a lg_last_avail()
macro.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Rusty Russell 2008-07-29 09:58:34 -05:00
parent cf485e566b
commit b5111790fa
1 changed files with 11 additions and 5 deletions
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16
Documentation/lguest/lguest.c
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@ -191,6 +191,9 @@ static void *_convert(struct iovec *iov, size_t size, size_t align,
return iov->iov_base;
}
/* Wrapper for the last available index. Makes it easier to change. */
#define lg_last_avail(vq) ((vq)->last_avail_idx)
/* The virtio configuration space is defined to be little-endian. x86 is
* little-endian too, but it's nice to be explicit so we have these helpers. */
#define cpu_to_le16(v16) (v16)
@ -690,19 +693,22 @@ static unsigned get_vq_desc(struct virtqueue *vq,
unsigned int *out_num, unsigned int *in_num)
{
unsigned int i, head;
u16 last_avail;
/* Check it isn't doing very strange things with descriptor numbers. */
if ((u16)(vq->vring.avail->idx - vq->last_avail_idx) > vq->vring.num)
last_avail = lg_last_avail(vq);
if ((u16)(vq->vring.avail->idx - last_avail) > vq->vring.num)
errx(1, "Guest moved used index from %u to %u",
vq->last_avail_idx, vq->vring.avail->idx);
last_avail, vq->vring.avail->idx);
/* If there's nothing new since last we looked, return invalid. */
if (vq->vring.avail->idx == vq->last_avail_idx)
if (vq->vring.avail->idx == last_avail)
return vq->vring.num;
/* Grab the next descriptor number they're advertising, and increment
* the index we've seen. */
head = vq->vring.avail->ring[vq->last_avail_idx++ % vq->vring.num];
head = vq->vring.avail->ring[last_avail % vq->vring.num];
lg_last_avail(vq)++;
/* If their number is silly, that's a fatal mistake. */
if (head >= vq->vring.num)
@ -980,7 +986,7 @@ static void update_device_status(struct device *dev)
for (vq = dev->vq; vq; vq = vq->next) {
memset(vq->vring.desc, 0,
vring_size(vq->config.num, getpagesize()));
vq->last_avail_idx = 0;
lg_last_avail(vq) = 0;
}
} else if (dev->desc->status & VIRTIO_CONFIG_S_FAILED) {
warnx("Device %s configuration FAILED", dev->name);