X-Git-Url: http://pilppa.org/gitweb/?a=blobdiff_plain;f=Documentation%2Fnetworking%2Fnetdevices.txt;h=d0f71fc7f7829b1dfb9dfc689afe0978bec53c76;hb=af0900537f90b58fcfb7a7c821c661be8301fc9b;hp=ce1361f952436e6c504fd1786009f03211508513;hpb=bb33808d282a48803dcb6070ee1547d221669114;p=linux-2.6-omap-h63xx.git

diff --git a/Documentation/networking/netdevices.txt b/Documentation/networking/netdevices.txt
index ce1361f9524..d0f71fc7f78 100644
--- a/Documentation/networking/netdevices.txt
+++ b/Documentation/networking/netdevices.txt
@@ -20,6 +20,30 @@ private data which gets freed when the network device is freed. If
 separately allocated data is attached to the network device
 (dev->priv) then it is up to the module exit handler to free that.
 
+MTU
+===
+Each network device has a Maximum Transfer Unit. The MTU does not
+include any link layer protocol overhead. Upper layer protocols must
+not pass a socket buffer (skb) to a device to transmit with more data
+than the mtu. The MTU does not include link layer header overhead, so
+for example on Ethernet if the standard MTU is 1500 bytes used, the
+actual skb will contain up to 1514 bytes because of the Ethernet
+header. Devices should allow for the 4 byte VLAN header as well.
+
+Segmentation Offload (GSO, TSO) is an exception to this rule.  The
+upper layer protocol may pass a large socket buffer to the device
+transmit routine, and the device will break that up into separate
+packets based on the current MTU.
+
+MTU is symmetrical and applies both to receive and transmit. A device
+must be able to receive at least the maximum size packet allowed by
+the MTU. A network device may use the MTU as mechanism to size receive
+buffers, but the device should allow packets with VLAN header. With
+standard Ethernet mtu of 1500 bytes, the device should allow up to
+1518 byte packets (1500 + 14 header + 4 tag).  The device may either:
+drop, truncate, or pass up oversize packets, but dropping oversize
+packets is preferred.
+
 
 struct net_device synchronization rules
 =======================================
@@ -43,16 +67,18 @@ dev->get_stats:
 
 dev->hard_start_xmit:
 	Synchronization: netif_tx_lock spinlock.
+
 	When the driver sets NETIF_F_LLTX in dev->features this will be
 	called without holding netif_tx_lock. In this case the driver
 	has to lock by itself when needed. It is recommended to use a try lock
-	for this and return -1 when the spin lock fails. 
+	for this and return NETDEV_TX_LOCKED when the spin lock fails.
 	The locking there should also properly protect against 
-	set_multicast_list
-	Context: Process with BHs disabled or BH (timer).
-	Notes: netif_queue_stopped() is guaranteed false
-               Interrupts must be enabled when calling hard_start_xmit.
-                (Interrupts must also be enabled when enabling the BH handler.)
+	set_multicast_list. Note that the use of NETIF_F_LLTX is deprecated.
+	Dont use it for new drivers.
+
+	Context: Process with BHs disabled or BH (timer),
+	         will be called with interrupts disabled by netconsole.
+
 	Return codes: 
 	o NETDEV_TX_OK everything ok. 
 	o NETDEV_TX_BUSY Cannot transmit packet, try later 
@@ -70,8 +96,13 @@ dev->set_multicast_list:
 	Synchronization: netif_tx_lock spinlock.
 	Context: BHs disabled
 
-dev->poll:
-	Synchronization: __LINK_STATE_RX_SCHED bit in dev->state.  See
-		dev_close code and comments in net/core/dev.c for more info.
+struct napi_struct synchronization rules
+========================================
+napi->poll:
+	Synchronization: NAPI_STATE_SCHED bit in napi->state.  Device
+		driver's dev->close method will invoke napi_disable() on
+		all NAPI instances which will do a sleeping poll on the
+		NAPI_STATE_SCHED napi->state bit, waiting for all pending
+		NAPI activity to cease.
 	Context: softirq
-
+	         will be called with interrupts disabled by netconsole.