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1da177e4 LT |
1 | |
2 | Network Devices, the Kernel, and You! | |
3 | ||
4 | ||
5 | Introduction | |
6 | ============ | |
7 | The following is a random collection of documentation regarding | |
8 | network devices. | |
9 | ||
10 | struct net_device allocation rules | |
11 | ================================== | |
12 | Network device structures need to persist even after module is unloaded and | |
13 | must be allocated with kmalloc. If device has registered successfully, | |
14 | it will be freed on last use by free_netdev. This is required to handle the | |
15 | pathologic case cleanly (example: rmmod mydriver </sys/class/net/myeth/mtu ) | |
16 | ||
17 | There are routines in net_init.c to handle the common cases of | |
18 | alloc_etherdev, alloc_netdev. These reserve extra space for driver | |
19 | private data which gets freed when the network device is freed. If | |
20 | separately 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 | ||
24 | struct net_device synchronization rules | |
25 | ======================================= | |
26 | dev->open: | |
27 | Synchronization: rtnl_lock() semaphore. | |
28 | Context: process | |
29 | ||
30 | dev->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 | ||
36 | dev->do_ioctl: | |
37 | Synchronization: rtnl_lock() semaphore. | |
38 | Context: process | |
39 | ||
40 | dev->get_stats: | |
41 | Synchronization: dev_base_lock rwlock. | |
42 | Context: nominally process, but don't sleep inside an rwlock | |
43 | ||
44 | dev->hard_start_xmit: | |
932ff279 | 45 | Synchronization: netif_tx_lock spinlock. |
1da177e4 | 46 | When the driver sets NETIF_F_LLTX in dev->features this will be |
932ff279 | 47 | called without holding netif_tx_lock. In this case the driver |
1da177e4 LT |
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 | |
aa77d269 BG |
54 | Interrupts must be enabled when calling hard_start_xmit. |
55 | (Interrupts must also be enabled when enabling the BH handler.) | |
1da177e4 LT |
56 | 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 | ||
64 | dev->tx_timeout: | |
932ff279 | 65 | Synchronization: netif_tx_lock spinlock. |
1da177e4 LT |
66 | Context: BHs disabled |
67 | Notes: netif_queue_stopped() is guaranteed true | |
68 | ||
69 | dev->set_multicast_list: | |
932ff279 | 70 | Synchronization: netif_tx_lock spinlock. |
1da177e4 LT |
71 | Context: BHs disabled |
72 | ||
73 | dev->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 |