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 kmalloc. 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 open: Synchronization: rtnl_lock() semaphore. Context: process dev->stop: Synchronization: rtnl_lock() semaphore. Context: process Note1: netif_running() is guaranteed false Note2: dev->poll() is guaranteed to be stopped dev->do_ioctl: Synchronization: rtnl_lock() semaphore. Context: process dev->get_stats: Synchronization: dev_base_lock rwlock. Context: nominally process, but don't sleep inside an rwlock 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 NETDEV_TX_LOCKED when the spin lock fails. The locking there should also properly protect against 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 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. o NETDEV_TX_LOCKED Locking failed, please retry quickly. Only valid when NETIF_F_LLTX is set. dev->tx_timeout: Synchronization: netif_tx_lock spinlock. Context: BHs disabled Notes: netif_queue_stopped() is guaranteed true dev->set_multicast_list: Synchronization: netif_tx_lock spinlock. Context: BHs disabled 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.