/*
* Write scattered channel packet to TX bufring.
*
* The offset of this channel packet is written as a 64bits value
* immediately after this channel packet.
*/
int
vmbus_txbr_write(struct vmbus_txbr *tbr, const struct iovec iov[], int iovlen,
boolean_t *need_sig)
{
uint32_t old_windex, windex, total;
uint64_t save_windex;
int i;
total = 0;
for (i = 0; i < iovlen; i++)
total += iov[i].iov_len;
total += sizeof(save_windex);
mtx_lock_spin(&tbr->txbr_lock);
/*
* NOTE:
* If this write is going to make br_windex same as br_rindex,
* i.e. the available space for write is same as the write size,
* we can't do it then, since br_windex == br_rindex means that
* the bufring is empty.
*/
if (vmbus_txbr_avail(tbr) <= total) {
mtx_unlock_spin(&tbr->txbr_lock);
return (EAGAIN);
}
/* Save br_windex for later use */
old_windex = tbr->txbr_windex;
/*
* Copy the scattered channel packet to the TX bufring.
*/
windex = old_windex;
for (i = 0; i < iovlen; i++) {
windex = vmbus_txbr_copyto(tbr, windex,
iov[i].iov_base, iov[i].iov_len);
}
/*
* Set the offset of the current channel packet.
*/
save_windex = ((uint64_t)old_windex) << 32;
windex = vmbus_txbr_copyto(tbr, windex, &save_windex,
sizeof(save_windex));
/*
* Update the write index _after_ the channel packet
* is copied.
*/
__compiler_membar();
tbr->txbr_windex = windex;
mtx_unlock_spin(&tbr->txbr_lock);
*need_sig = vmbus_txbr_need_signal(tbr, old_windex);
return (0);
}
/*
* Write scattered channel packet to TX bufring.
*
* The offset of this channel packet is written as a 64bits value
* immediately after this channel packet.
*
* The write goes through three stages:
* 1. Reserve space in ring buffer for the new data.
* Writer atomically moves priv_write_index.
* 2. Copy the new data into the ring.
* 3. Update the tail of the ring (visible to host) that indicates
* next read location. Writer updates write_index
*/
int
vmbus_txbr_write(struct vmbus_br *tbr, const struct iovec iov[], int iovlen,
bool *need_sig)
{
struct vmbus_bufring *vbr = tbr->vbr;
uint32_t ring_size = tbr->dsize;
uint32_t old_windex, next_windex, windex, total;
uint64_t save_windex;
int i;
total = 0;
for (i = 0; i < iovlen; i++)
total += iov[i].iov_len;
total += sizeof(save_windex);
/* Reserve space in ring */
do {
uint32_t avail;
/* Get current free location */
old_windex = tbr->windex;
/* Prevent compiler reordering this with calculation */
rte_compiler_barrier();
avail = vmbus_br_availwrite(tbr, old_windex);
/* If not enough space in ring, then tell caller. */
if (avail <= total)
return -EAGAIN;
next_windex = vmbus_br_idxinc(old_windex, total, ring_size);
/* Atomic update of next write_index for other threads */
} while (!rte_atomic32_cmpset(&tbr->windex, old_windex, next_windex));
/* Space from old..new is now reserved */
windex = old_windex;
for (i = 0; i < iovlen; i++) {
windex = vmbus_txbr_copyto(tbr, windex,
iov[i].iov_base, iov[i].iov_len);
}
/* Set the offset of the current channel packet. */
save_windex = ((uint64_t)old_windex) << 32;
windex = vmbus_txbr_copyto(tbr, windex, &save_windex,
sizeof(save_windex));
/* The region reserved should match region used */
RTE_ASSERT(windex == next_windex);
/* Ensure that data is available before updating host index */
rte_smp_wmb();
/* Checkin for our reservation. wait for our turn to update host */
while (!rte_atomic32_cmpset(&vbr->windex, old_windex, next_windex))
rte_pause();
/* If host had read all data before this, then need to signal */
*need_sig |= vmbus_txbr_need_signal(tbr, old_windex);
return 0;
}
