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Diffstat (limited to 'Documentation/networking/netdevices.txt')
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diff --git a/Documentation/networking/netdevices.txt b/Documentation/networking/netdevices.txt deleted file mode 100644 index 7fec2061a334..000000000000 --- a/Documentation/networking/netdevices.txt +++ /dev/null @@ -1,104 +0,0 @@ - -Network Devices, the Kernel, and You! - - -Introduction -============ -The following is a random collection of documentation regarding -network devices. - -struct net_device allocation rules -================================== -Network device structures need to persist even after module is unloaded and -must be allocated with alloc_netdev_mqs() and friends. -If device has registered successfully, it will be freed on last use -by free_netdev(). This is required to handle the pathologic case cleanly -(example: rmmod mydriver </sys/class/net/myeth/mtu ) - -alloc_netdev_mqs()/alloc_netdev() 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 -(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 -======================================= -ndo_open: - Synchronization: rtnl_lock() semaphore. - Context: process - -ndo_stop: - Synchronization: rtnl_lock() semaphore. - Context: process - Note: netif_running() is guaranteed false - -ndo_do_ioctl: - Synchronization: rtnl_lock() semaphore. - Context: process - -ndo_get_stats: - Synchronization: dev_base_lock rwlock. - Context: nominally process, but don't sleep inside an rwlock - -ndo_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. - The locking there should also properly protect against - set_rx_mode. WARNING: 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 - Usually a bug, means queue start/stop flow control is broken in - the driver. Note: the driver must NOT put the skb in its DMA ring. - -ndo_tx_timeout: - Synchronization: netif_tx_lock spinlock; all TX queues frozen. - Context: BHs disabled - Notes: netif_queue_stopped() is guaranteed true - -ndo_set_rx_mode: - Synchronization: netif_addr_lock spinlock. - Context: BHs disabled - -struct napi_struct synchronization rules -======================================== -napi->poll: - Synchronization: NAPI_STATE_SCHED bit in napi->state. Device - driver's ndo_stop 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. |