alloc_etherdev, alloc_netdev. These reserve extra space for driver
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.
+(netdev_priv(dev)) 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
Context: nominally process, but don't sleep inside an rwlock
dev->hard_start_xmit:
- Synchronization: dev->xmit_lock spinlock.
+ Synchronization: netif_tx_lock spinlock.
+
When the driver sets NETIF_F_LLTX in dev->features this will be
- called without holding xmit_lock. In this case the driver
+ 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: BHs disabled
- Notes: netif_queue_stopped() is guaranteed false
+ set_multicast_list. Note that the use of NETIF_F_LLTX is deprecated.
+ Don't 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
Only valid when NETIF_F_LLTX is set.
dev->tx_timeout:
- Synchronization: dev->xmit_lock spinlock.
+ Synchronization: netif_tx_lock spinlock.
Context: BHs disabled
Notes: netif_queue_stopped() is guaranteed true
dev->set_multicast_list:
- Synchronization: dev->xmit_lock spinlock.
+ 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.