/**
* returns -1 on error, or size on success
*/
static int do_send(struct libvchan *ctrl, const void *data, size_t size)
{
int real_idx = wr_prod(ctrl) & (wr_ring_size(ctrl) - 1);
int avail_contig = wr_ring_size(ctrl) - real_idx;
if (VCHAN_DEBUG) {
char metainfo[32];
struct iovec iov[2];
iov[0].iov_base = metainfo;
iov[0].iov_len = snprintf(metainfo, 32, "vchan wr %d/%d", ctrl->other_domain_id, ctrl->device_number);
iov[1].iov_base = (void *)data;
iov[1].iov_len = size;
writev(-1, iov, 2);
}
if (avail_contig > size)
avail_contig = size;
memcpy(wr_ring(ctrl) + real_idx, data, avail_contig);
if (avail_contig < size)
{
// we rolled across the end of the ring
memcpy(wr_ring(ctrl), data + avail_contig, size - avail_contig);
}
barrier(); // data must be in the ring prior to increment
wr_prod(ctrl) += size;
barrier(); // increment must happen prior to notify
if (do_notify(ctrl) < 0)
return -1;
return size;
}
/**
* Get the amount of buffer space available, and do nothing
* about notifications
*/
static inline int raw_get_buffer_space(struct libxenvchan *ctrl)
{
uint32_t ready = wr_ring_size(ctrl) - (wr_prod(ctrl) - wr_cons(ctrl));
if (ready > wr_ring_size(ctrl))
/* We have no way to return errors. Locking up the ring is
* better than the alternatives. */
return 0;
return ready;
}
/**
* Get the amount of buffer space available and enable notifications if needed.
*/
static inline int fast_get_buffer_space(struct libxenvchan *ctrl, size_t request)
{
int ready = wr_ring_size(ctrl) - (wr_prod(ctrl) - wr_cons(ctrl));
if (ready >= request)
return ready;
/* We plan to fill the buffer; please tell us when you've read it */
request_notify(ctrl, VCHAN_NOTIFY_READ);
/*
* If the reader moved wr_cons after our read but before request, we
* will not get notified even though the actual amount of buffer space
* is above request. Reread wr_cons to cover this case.
*/
return wr_ring_size(ctrl) - (wr_prod(ctrl) - wr_cons(ctrl));
}
int libxenvchan_buffer_space(struct libxenvchan *ctrl)
{
/* Since this value is being used outside libxenvchan, request notification
* when it changes
*/
request_notify(ctrl, VCHAN_NOTIFY_READ);
return wr_ring_size(ctrl) - (wr_prod(ctrl) - wr_cons(ctrl));
}
/**
* returns -1 on error, or size on success
*/
static int do_send(struct libxenvchan *ctrl, const void *data, size_t size)
{
int real_idx = wr_prod(ctrl) & (wr_ring_size(ctrl) - 1);
int avail_contig = wr_ring_size(ctrl) - real_idx;
if (avail_contig > size)
avail_contig = size;
xen_mb(); /* read indexes /then/ write data */
memcpy(wr_ring(ctrl) + real_idx, data, avail_contig);
if (avail_contig < size)
{
// we rolled across the end of the ring
memcpy(wr_ring(ctrl), data + avail_contig, size - avail_contig);
}
xen_wmb(); /* write data /then/ notify */
wr_prod(ctrl) += size;
if (send_notify(ctrl, VCHAN_NOTIFY_WRITE))
return -1;
return size;
}
/**
* returns 0 if no buffer space is available, -1 on error, or size on success
*/
int libxenvchan_send(struct libxenvchan *ctrl, const void *data, size_t size)
{
int avail;
while (1) {
if (!libxenvchan_is_open(ctrl))
return -1;
avail = fast_get_buffer_space(ctrl, size);
if (size <= avail)
return do_send(ctrl, data, size);
if (!ctrl->blocking)
return 0;
if (size > wr_ring_size(ctrl))
return -1;
if (libxenvchan_wait(ctrl))
return -1;
}
}
int libvchan_buffer_space(struct libvchan *ctrl)
{
return wr_ring_size(ctrl) - (wr_prod(ctrl) - wr_cons(ctrl));
}