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Linus Torvalds1da177e2005-04-16 15:20:36 -07001
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
Ben Greearaa77d262005-04-24 20:13:19 -070054 Interrupts must be enabled when calling hard_start_xmit.
55 (Interrupts must also be enabled when enabling the BH handler.)
Linus Torvalds1da177e2005-04-16 15:20:36 -070056 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: dev->xmit_lock spinlock.
66 Context: BHs disabled
67 Notes: netif_queue_stopped() is guaranteed true
68
69dev->set_multicast_list:
70 Synchronization: dev->xmit_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