Author: adrian
Date: Wed May 27 05:37:04 2009
New Revision: 192875
URL: http://svn.freebsd.org/changeset/base/192875
Log:
Comment tidyup; comment where the next explicit check should
appear.
Modified:
head/sys/dev/xen/netfront/netfront.c
Modified: head/sys/dev/xen/netfront/netfront.c
==============================================================================
--- head/sys/dev/xen/netfront/netfront.c Wed May 27 05:18:13 2009
(r192874)
+++ head/sys/dev/xen/netfront/netfront.c Wed May 27 05:37:04 2009
(r192875)
@@ -1446,30 +1446,42 @@ xn_start_locked(struct ifnet *ifp)
nfrags++;
/*
- * Don't attempt to queue this packet if there aren't enough
free entries in the chain.
- * There isn't a 1:1 correspondance between the mbuf TX ring
and the xenbus TX ring.
+ * Don't attempt to queue this packet if there aren't
+ * enough free entries in the chain.
+ *
+ * There isn't a 1:1 correspondance between the mbuf TX ring
+ * and the xenbus TX ring.
* xn_txeof() may need to be called to free up some slots.
*
- * It is quite possible that this can be later eliminated if it
turns out that partial
- * packets can be pushed into the ringbuffer, with fragments
pushed in when further slots
+ * It is quite possible that this can be later eliminated if
+ * it turns out that partial * packets can be pushed into
+ * the ringbuffer, with fragments pushed in when further slots
* free up.
*
- * It is also quite possible that the driver will lock up - Xen
may not send another
- * interrupt to kick the tx/rx processing if the xenbus RX ring
is full and xenbus TX ring
- * is empty - no further TX work can be done until space is
made in the TX mbuf ring and
- * the RX side may be waiting for TX data to continue. It is
quite possible some timer
- * event should be created to kick TX/RX processing along in
certain conditions.
+ * It is also quite possible that the driver will lock up
+ * if the TX queue fills up with no RX traffic, and
+ * the mbuf ring is exhausted. The queue may need
+ * a swift kick to continue.
*/
- /* its not +1 like the allocation because we need to keep slot
[0] free for the freelist head */
+ /*
+ * It is not +1 like the allocation because we need to keep
+ * slot [0] free for the freelist head
+ */
if (sc->xn_cdata.xn_tx_chain_cnt + nfrags >= NET_TX_RING_SIZE) {
printf("xn_start_locked: xn_tx_chain_cnt (%d) + nfrags
%d >= NET_TX_RING_SIZE (%d); must be full!\n",
- (int) sc->xn_cdata.xn_tx_chain_cnt, (int) nfrags,
(int) NET_TX_RING_SIZE);
+ (int) sc->xn_cdata.xn_tx_chain_cnt,
+ (int) nfrags, (int) NET_TX_RING_SIZE);
IF_PREPEND(&ifp->if_snd, m_head);
ifp->if_drv_flags |= IFF_DRV_OACTIVE;
break;
}
+ /*
+ * XXX TODO - make sure there's actually space available
+ * in the Xen TX ring for this rather than the hacky way
+ * its currently done.
+ */
/*
* Start packing the mbufs in this chain into
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