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
=======================================
dev->open:
has to lock by itself when needed. It is recommended to use a try lock
for this and return NETDEV_TX_LOCKED when the spin lock fails.
The locking there should also properly protect against
- set_multicast_list.
+ 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.
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.
-