static int do_recv(struct libvchan *ctrl, void *data, size_t size)
{
int real_idx = rd_cons(ctrl) & (rd_ring_size(ctrl) - 1);
int avail_contig = rd_ring_size(ctrl) - real_idx;
if (avail_contig > size)
avail_contig = size;
barrier(); // data read must happen after rd_cons read
memcpy(data, rd_ring(ctrl) + real_idx, avail_contig);
if (avail_contig < size)
{
// we rolled across the end of the ring
memcpy(data + avail_contig, rd_ring(ctrl), size - avail_contig);
}
rd_cons(ctrl) += size;
if (VCHAN_DEBUG) {
char metainfo[32];
struct iovec iov[2];
iov[0].iov_base = metainfo;
iov[0].iov_len = snprintf(metainfo, 32, "vchan rd %d/%d", ctrl->other_domain_id, ctrl->device_number);
iov[1].iov_base = data;
iov[1].iov_len = size;
writev(-1, iov, 2);
}
barrier(); // consumption must happen prior to notify of newly freed space
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_data_ready(struct libxenvchan *ctrl)
{
uint32_t ready = rd_prod(ctrl) - rd_cons(ctrl);
if (ready >= rd_ring_size(ctrl))
/* We have no way to return errors. Locking up the ring is
* better than the alternatives. */
return 0;
return ready;
}
static int do_recv(struct libxenvchan *ctrl, void *data, size_t size)
{
int real_idx = rd_cons(ctrl) & (rd_ring_size(ctrl) - 1);
int avail_contig = rd_ring_size(ctrl) - real_idx;
if (avail_contig > size)
avail_contig = size;
xen_rmb(); /* data read must happen /after/ rd_cons read */
memcpy(data, rd_ring(ctrl) + real_idx, avail_contig);
if (avail_contig < size)
{
// we rolled across the end of the ring
memcpy(data + avail_contig, rd_ring(ctrl), size - avail_contig);
}
xen_mb(); /* consume /then/ notify */
rd_cons(ctrl) += size;
if (send_notify(ctrl, VCHAN_NOTIFY_READ))
return -1;
return size;
}
/**
* reads exactly size bytes from the vchan.
* returns 0 if insufficient data is available, -1 on error, or size on success
*/
int libxenvchan_recv(struct libxenvchan *ctrl, void *data, size_t size)
{
while (1) {
int avail = fast_get_data_ready(ctrl, size);
if (size <= avail)
return do_recv(ctrl, data, size);
if (!libxenvchan_is_open(ctrl))
return -1;
if (!ctrl->blocking)
return 0;
if (size > rd_ring_size(ctrl))
return -1;
if (libxenvchan_wait(ctrl))
return -1;
}
}