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Comment tidyup; comment where the next explicit check should

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appear.
This commit is contained in:
adrian 2009-05-27 05:37:04 +00:00
parent c6ef0a3a39
commit 5923b72e4e
1 changed files with 23 additions and 11 deletions
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34
sys/dev/xen/netfront/netfront.c
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@ -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