Blame view
Documentation/networking/netdevices.txt
4.09 KB
1da177e4c Linux-2.6.12-rc2 |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 |
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 </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 private data which gets freed when the network device is freed. If separately allocated data is attached to the network device |
b74ca3a89 netdevice: Kill n... |
21 |
(netdev_priv(dev)) then it is up to the module exit handler to free that. |
1da177e4c Linux-2.6.12-rc2 |
22 |
|
1c8c7d641 [NET]: netdevice ... |
23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 |
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. |
1da177e4c Linux-2.6.12-rc2 |
46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 |
struct net_device synchronization rules ======================================= dev->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: |
932ff279a [NET]: Add netif_... |
67 |
Synchronization: netif_tx_lock spinlock. |
172293332 [NET]: netdevice ... |
68 |
|
1da177e4c Linux-2.6.12-rc2 |
69 |
When the driver sets NETIF_F_LLTX in dev->features this will be |
932ff279a [NET]: Add netif_... |
70 |
called without holding netif_tx_lock. In this case the driver |
1da177e4c Linux-2.6.12-rc2 |
71 |
has to lock by itself when needed. It is recommended to use a try lock |
172293332 [NET]: netdevice ... |
72 |
for this and return NETDEV_TX_LOCKED when the spin lock fails. |
1da177e4c Linux-2.6.12-rc2 |
73 |
The locking there should also properly protect against |
e24eb521f [NET]: note that ... |
74 |
set_multicast_list. Note that the use of NETIF_F_LLTX is deprecated. |
19f594600 trivial: Miscella... |
75 |
Don't use it for new drivers. |
172293332 [NET]: netdevice ... |
76 77 78 |
Context: Process with BHs disabled or BH (timer), will be called with interrupts disabled by netconsole. |
1da177e4c Linux-2.6.12-rc2 |
79 80 81 82 83 84 85 86 87 |
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: |
932ff279a [NET]: Add netif_... |
88 |
Synchronization: netif_tx_lock spinlock. |
1da177e4c Linux-2.6.12-rc2 |
89 90 91 92 |
Context: BHs disabled Notes: netif_queue_stopped() is guaranteed true dev->set_multicast_list: |
932ff279a [NET]: Add netif_... |
93 |
Synchronization: netif_tx_lock spinlock. |
1da177e4c Linux-2.6.12-rc2 |
94 |
Context: BHs disabled |
bea3348ee [NET]: Make NAPI ... |
95 96 97 98 99 100 101 102 |
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. |
1da177e4c Linux-2.6.12-rc2 |
103 |
Context: softirq |
172293332 [NET]: netdevice ... |
104 |
will be called with interrupts disabled by netconsole. |