diff options
Diffstat (limited to 'Documentation/networking/netdevices.txt')
| -rw-r--r-- | Documentation/networking/netdevices.txt | 88 |
1 files changed, 59 insertions, 29 deletions
diff --git a/Documentation/networking/netdevices.txt b/Documentation/networking/netdevices.txt index 3c0a5ba614d..0b1cf6b2a59 100644 --- a/Documentation/networking/netdevices.txt +++ b/Documentation/networking/netdevices.txt @@ -10,49 +10,74 @@ 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 </sys/class/net/myeth/mtu ) +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 ) -There are routines in net_init.c to handle the common cases of -alloc_etherdev, alloc_netdev. These reserve extra space for driver +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 -(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 ======================================= -dev->open: +ndo_open: Synchronization: rtnl_lock() semaphore. Context: process -dev->stop: +ndo_stop: Synchronization: rtnl_lock() semaphore. Context: process - Note1: netif_running() is guaranteed false - Note2: dev->poll() is guaranteed to be stopped + Note: netif_running() is guaranteed false -dev->do_ioctl: +ndo_do_ioctl: Synchronization: rtnl_lock() semaphore. Context: process -dev->get_stats: +ndo_get_stats: Synchronization: dev_base_lock rwlock. Context: nominally process, but don't sleep inside an rwlock -dev->hard_start_xmit: - Synchronization: dev->xmit_lock spinlock. +ndo_start_xmit: + 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 - Interrupts must be enabled when calling hard_start_xmit. - (Interrupts must also be enabled when enabling the BH handler.) + set_rx_mode. 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 @@ -61,17 +86,22 @@ dev->hard_start_xmit: o NETDEV_TX_LOCKED Locking failed, please retry quickly. Only valid when NETIF_F_LLTX is set. -dev->tx_timeout: - Synchronization: dev->xmit_lock spinlock. +ndo_tx_timeout: + Synchronization: netif_tx_lock spinlock; all TX queues frozen. Context: BHs disabled Notes: netif_queue_stopped() is guaranteed true -dev->set_multicast_list: - Synchronization: dev->xmit_lock spinlock. +ndo_set_rx_mode: + Synchronization: netif_addr_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 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. |