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/Documentation/networking/netdevices.txt

https://bitbucket.org/evzijst/gittest
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 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: dev->xmit_lock spinlock.
46	When the driver sets NETIF_F_LLTX in dev->features this will be
47	called without holding xmit_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: BHs disabled
53	Notes: netif_queue_stopped() is guaranteed false
54	Return codes: 
55	o NETDEV_TX_OK everything ok. 
56	o NETDEV_TX_BUSY Cannot transmit packet, try later 
57	  Usually a bug, means queue start/stop flow control is broken in
58	  the driver. Note: the driver must NOT put the skb in its DMA ring.
59	o NETDEV_TX_LOCKED Locking failed, please retry quickly.
60	  Only valid when NETIF_F_LLTX is set.
61
62dev->tx_timeout:
63	Synchronization: dev->xmit_lock spinlock.
64	Context: BHs disabled
65	Notes: netif_queue_stopped() is guaranteed true
66
67dev->set_multicast_list:
68	Synchronization: dev->xmit_lock spinlock.
69	Context: BHs disabled
70
71dev->poll:
72	Synchronization: __LINK_STATE_RX_SCHED bit in dev->state.  See
73		dev_close code and comments in net/core/dev.c for more info.
74	Context: softirq
75