1 2Network Devices, the Kernel, and You! 3 4 5Introduction 6============ 7The following is a random collection of documentation regarding 8network devices. 9 10struct net_device allocation rules 11================================== 12Network device structures need to persist even after module is unloaded and 13must be allocated with kmalloc. If device has registered successfully, 14it will be freed on last use by free_netdev. This is required to handle the 15pathologic case cleanly (example: rmmod mydriver </sys/class/net/myeth/mtu ) 16 17There are routines in net_init.c to handle the common cases of 18alloc_etherdev, alloc_netdev. These reserve extra space for driver 19private data which gets freed when the network device is freed. If 20separately allocated data is attached to the network device 21(dev->priv) then it is up to the module exit handler to free that. 22 23 24struct net_device synchronization rules 25======================================= 26dev->open: 27 Synchronization: rtnl_lock() semaphore. 28 Context: process 29 30dev->stop: 31 Synchronization: rtnl_lock() semaphore. 32 Context: process 33 Note1: netif_running() is guaranteed false 34 Note2: dev->poll() is guaranteed to be stopped 35 36dev->do_ioctl: 37 Synchronization: rtnl_lock() semaphore. 38 Context: process 39 40dev->get_stats: 41 Synchronization: dev_base_lock rwlock. 42 Context: nominally process, but don't sleep inside an rwlock 43 44dev->hard_start_xmit: 45 Synchronization: netif_tx_lock spinlock. 46 When the driver sets NETIF_F_LLTX in dev->features this will be 47 called without holding netif_tx_lock. In this case the driver 48 has to lock by itself when needed. It is recommended to use a try lock 49 for this and return -1 when the spin lock fails. 50 The locking there should also properly protect against 51 set_multicast_list 52 Context: Process with BHs disabled or BH (timer). 53 Notes: netif_queue_stopped() is guaranteed false 54 Interrupts must be enabled when calling hard_start_xmit. 55 (Interrupts must also be enabled when enabling the BH handler.) 56 Return codes: 57 o NETDEV_TX_OK everything ok. 58 o NETDEV_TX_BUSY Cannot transmit packet, try later 59 Usually a bug, means queue start/stop flow control is broken in 60 the driver. Note: the driver must NOT put the skb in its DMA ring. 61 o NETDEV_TX_LOCKED Locking failed, please retry quickly. 62 Only valid when NETIF_F_LLTX is set. 63 64dev->tx_timeout: 65 Synchronization: netif_tx_lock spinlock. 66 Context: BHs disabled 67 Notes: netif_queue_stopped() is guaranteed true 68 69dev->set_multicast_list: 70 Synchronization: netif_tx_lock spinlock. 71 Context: BHs disabled 72 73dev->poll: 74 Synchronization: __LINK_STATE_RX_SCHED bit in dev->state. See 75 dev_close code and comments in net/core/dev.c for more info. 76 Context: softirq 77