Linux-2.6.12-rc2v2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!

1 files changed, 94 insertions, 0 deletions

diff --git a/Documentation/networking/driver.txt b/Documentation/networking/driver.txt
new file mode 100644
index 000000000000..11fd0ef5ff57
--- /dev/null
+++ b/Documentation/networking/driver.txt
@@ -0,0 +1,94 @@
+Documents about softnet driver issues in general can be found
+at:
+
+        http://www.firstfloor.org/~andi/softnet/
+
+Transmit path guidelines:
+
+1) The hard_start_xmit method must never return '1' under any
+   normal circumstances.  It is considered a hard error unless
+   there is no way your device can tell ahead of time when it's
+   transmit function will become busy.
+
+   Instead it must maintain the queue properly.  For example,
+   for a driver implementing scatter-gather this means:
+
+        static int drv_hard_start_xmit(struct sk_buff *skb,
+                                       struct net_device *dev)
+        {
+                struct drv *dp = dev->priv;
+
+                lock_tx(dp);
+                ...
+                /* This is a hard error log it. */
+                if (TX_BUFFS_AVAIL(dp) <= (skb_shinfo(skb)->nr_frags + 1)) {
+                        netif_stop_queue(dev);
+                        unlock_tx(dp);
+                        printk(KERN_ERR PFX "%s: BUG! Tx Ring full when queue awake!\n",
+                               dev->name);
+                        return 1;
+                }
+
+                ... queue packet to card ...
+                ... update tx consumer index ...
+
+                if (TX_BUFFS_AVAIL(dp) <= (MAX_SKB_FRAGS + 1))
+                        netif_stop_queue(dev);
+
+                ...
+                unlock_tx(dp);
+                ...
+        }
+
+   And then at the end of your TX reclaimation event handling:
+
+        if (netif_queue_stopped(dp->dev) &&
+            TX_BUFFS_AVAIL(dp) > (MAX_SKB_FRAGS + 1))
+                netif_wake_queue(dp->dev);
+
+   For a non-scatter-gather supporting card, the three tests simply become:
+
+                /* This is a hard error log it. */
+                if (TX_BUFFS_AVAIL(dp) <= 0)
+
+   and:
+
+                if (TX_BUFFS_AVAIL(dp) == 0)
+
+   and:
+
+        if (netif_queue_stopped(dp->dev) &&
+            TX_BUFFS_AVAIL(dp) > 0)
+                netif_wake_queue(dp->dev);
+
+2) Do not forget to update netdev->trans_start to jiffies after
+   each new tx packet is given to the hardware.
+
+3) Do not forget that once you return 0 from your hard_start_xmit
+   method, it is your driver's responsibility to free up the SKB
+   and in some finite amount of time.
+
+   For example, this means that it is not allowed for your TX
+   mitigation scheme to let TX packets "hang out" in the TX
+   ring unreclaimed forever if no new TX packets are sent.
+   This error can deadlock sockets waiting for send buffer room
+   to be freed up.
+
+   If you return 1 from the hard_start_xmit method, you must not keep
+   any reference to that SKB and you must not attempt to free it up.
+
+Probing guidelines:
+
+1) Any hardware layer address you obtain for your device should
+   be verified.  For example, for ethernet check it with
+   linux/etherdevice.h:is_valid_ether_addr()
+
+Close/stop guidelines:
+
+1) After the dev->stop routine has been called, the hardware must
+   not receive or transmit any data.  All in flight packets must
+   be aborted. If necessary, poll or wait for completion of 
+   any reset commands.
+
+2) The dev->stop routine will be called by unregister_netdevice
+   if device is still UP.