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Index: head/sys/dev/hyperv/vmbus/hv_ring_buffer.c
===================================================================
--- head/sys/dev/hyperv/vmbus/hv_ring_buffer.c
+++ head/sys/dev/hyperv/vmbus/hv_ring_buffer.c
@@ -144,25 +144,23 @@
/*
* Now check to see if the ring buffer is still empty.
* If it is not, we raced and we need to process new
- * incoming messages.
+ * incoming channel packets.
*/
return vmbus_rxbr_avail(rbr);
}
/*
- * When we write to the ring buffer, check if the host needs to
- * be signaled. Here is the details of this protocol:
+ * When we write to the ring buffer, check if the host needs to be
+ * signaled.
*
- * 1. The host guarantees that while it is draining the
- * ring buffer, it will set the interrupt_mask to
- * indicate it does not need to be interrupted when
- * new data is placed.
- *
- * 2. The host guarantees that it will completely drain
- * the ring buffer before exiting the read loop. Further,
- * once the ring buffer is empty, it will clear the
- * interrupt_mask and re-check to see if new data has
- * arrived.
+ * The contract:
+ * - The host guarantees that while it is draining the TX bufring,
+ * it will set the br_imask to indicate it does not need to be
+ * interrupted when new data are added.
+ * - The host guarantees that it will completely drain the TX bufring
+ * before exiting the read loop. Further, once the TX bufring is
+ * empty, it will clear the br_imask and re-check to see if new
+ * data have arrived.
*/
static boolean_t
hv_ring_buffer_needsig_on_write(uint32_t old_write_location,
@@ -172,8 +170,10 @@
if (tbr->txbr_imask)
return (FALSE);
+ /* XXX only compiler fence is needed */
/* Read memory barrier */
rmb();
+
/*
* This is the only case we need to signal when the
* ring transitions from being empty to non-empty.
@@ -252,7 +252,6 @@
for (i = 0; i < iovlen; i++)
total_bytes_to_write += iov[i].iov_len;
-
total_bytes_to_write += sizeof(uint64_t);
mtx_lock_spin(&tbr->txbr_lock);
@@ -260,9 +259,11 @@
byte_avail_to_write = vmbus_txbr_avail(tbr);
/*
- * If there is only room for the packet, assume it is full.
- * Otherwise, the next time around, we think the ring buffer
- * is empty since the read index == write index
+ * 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 (byte_avail_to_write <= total_bytes_to_write) {
mtx_unlock_spin(&tbr->txbr_lock);
@@ -270,7 +271,7 @@
}
/*
- * Write to the ring buffer
+ * Copy the scattered channel packet to the TX bufring.
*/
next_write_location = tbr->txbr_windex;
@@ -282,20 +283,20 @@
}
/*
- * Set previous packet start
+ * Set the offset of the current channel packet.
*/
prev_indices = ((uint64_t)tbr->txbr_windex) << 32;
-
next_write_location = copy_to_ring_buffer(tbr,
next_write_location, (char *)&prev_indices, sizeof(uint64_t));
/*
+ * XXX only compiler fence is needed.
* Full memory barrier before upding the write index.
*/
mb();
/*
- * Now, update the write location
+ * Now, update the write index.
*/
tbr->txbr_windex = next_write_location;
@@ -315,20 +316,12 @@
mtx_lock_spin(&rbr->rxbr_lock);
bytesAvailToRead = vmbus_rxbr_avail(rbr);
-
- /*
- * Make sure there is something to read
- */
if (bytesAvailToRead < dlen) {
mtx_unlock_spin(&rbr->rxbr_lock);
return (EAGAIN);
}
- /*
- * Convert to byte offset
- */
nextReadLocation = rbr->rxbr_rindex;
-
nextReadLocation = copy_from_ring_buffer(rbr, data, dlen,
nextReadLocation);
@@ -349,24 +342,27 @@
mtx_lock_spin(&rbr->rxbr_lock);
bytes_avail_to_read = vmbus_rxbr_avail(rbr);
-
- /*
- * Make sure there is something to read
- */
if (bytes_avail_to_read < dlen) {
mtx_unlock_spin(&rbr->rxbr_lock);
return (EAGAIN);
}
+ /*
+ * Copy channel packet from RX bufring.
+ */
next_read_location = (rbr->rxbr_rindex + offset) % rbr->rxbr_dsize;
-
next_read_location = copy_from_ring_buffer(rbr, data, dlen,
next_read_location);
+ /*
+ * Discard this channel packet's start offset, which is useless
+ * for us.
+ */
next_read_location = copy_from_ring_buffer(rbr,
(char *)&prev_indices, sizeof(uint64_t), next_read_location);
/*
+ * XXX only compiler fence is needed.
* Make sure all reads are done before we update the read index since
* the writer may start writing to the read area once the read index
* is updated.
@@ -383,11 +379,6 @@
return (0);
}
-/**
- * @brief Helper routine to copy from source to ring buffer.
- *
- * Assume there is enough room. Handles wrap-around in dest case only!
- */
static uint32_t
copy_to_ring_buffer(const struct vmbus_txbr *tbr,
uint32_t start_write_offset, const uint8_t *src, uint32_t src_len)
@@ -397,7 +388,7 @@
uint32_t fragLen;
if (src_len > ring_buffer_size - start_write_offset) {
- /* wrap-around detected! */
+ /* Wrap-around detected! */
fragLen = ring_buffer_size - start_write_offset;
memcpy(ring_buffer + start_write_offset, src, fragLen);
memcpy(ring_buffer, src + fragLen, src_len - fragLen);
@@ -411,11 +402,6 @@
return (start_write_offset);
}
-/**
- * @brief Helper routine to copy to source from ring buffer.
- *
- * Assume there is enough room. Handles wrap-around in src case only!
- */
static uint32_t
copy_from_ring_buffer(const struct vmbus_rxbr *rbr, char *dest,
uint32_t dest_len, uint32_t start_read_offset)
@@ -425,7 +411,7 @@
uint32_t ring_buffer_size = rbr->rxbr_dsize;
if (dest_len > ring_buffer_size - start_read_offset) {
- /* wrap-around detected at the src */
+ /* Wrap-around detected at the src */
fragLen = ring_buffer_size - start_read_offset;
memcpy(dest, ring_buffer + start_read_offset, fragLen);
memcpy(dest + fragLen, ring_buffer, dest_len - fragLen);

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