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Linus Torvalds1da177e2005-04-16 15:20:36 -07001
2________________
3NETIF Msg Level
4
5The design of the network interface message level setting.
6
7History
8
9 The design of the debugging message interface was guided and
10 constrained by backwards compatibility previous practice. It is useful
11 to understand the history and evolution in order to understand current
12 practice and relate it to older driver source code.
13
14 From the beginning of Linux, each network device driver has had a local
15 integer variable that controls the debug message level. The message
16 level ranged from 0 to 7, and monotonically increased in verbosity.
17
18 The message level was not precisely defined past level 3, but were
19 always implemented within +-1 of the specified level. Drivers tended
20 to shed the more verbose level messages as they matured.
21 0 Minimal messages, only essential information on fatal errors.
22 1 Standard messages, initialization status. No run-time messages
23 2 Special media selection messages, generally timer-driver.
24 3 Interface starts and stops, including normal status messages
25 4 Tx and Rx frame error messages, and abnormal driver operation
26 5 Tx packet queue information, interrupt events.
27 6 Status on each completed Tx packet and received Rx packets
28 7 Initial contents of Tx and Rx packets
29
30 Initially this message level variable was uniquely named in each driver
31 e.g. "lance_debug", so that a kernel symbolic debugger could locate and
32 modify the setting. When kernel modules became common, the variables
33 were consistently renamed to "debug" and allowed to be set as a module
34 parameter.
35
36 This approach worked well. However there is always a demand for
37 additional features. Over the years the following emerged as
38 reasonable and easily implemented enhancements
39 Using an ioctl() call to modify the level.
40 Per-interface rather than per-driver message level setting.
41 More selective control over the type of messages emitted.
42
Matt LaPlanted6bc8ac2006-10-03 22:54:15 +020043 The netif_msg recommendation adds these features with only a minor
Linus Torvalds1da177e2005-04-16 15:20:36 -070044 complexity and code size increase.
45
46 The recommendation is the following points
47 Retaining the per-driver integer variable "debug" as a module
48 parameter with a default level of '1'.
49
50 Adding a per-interface private variable named "msg_enable". The
51 variable is a bit map rather than a level, and is initialized as
52 1 << debug
53 Or more precisely
54 debug < 0 ? 0 : 1 << min(sizeof(int)-1, debug)
55
56 Messages should changes from
57 if (debug > 1)
58 printk(MSG_DEBUG "%s: ...
59 to
60 if (np->msg_enable & NETIF_MSG_LINK)
61 printk(MSG_DEBUG "%s: ...
62
63
64The set of message levels is named
65 Old level Name Bit position
66 0 NETIF_MSG_DRV 0x0001
67 1 NETIF_MSG_PROBE 0x0002
68 2 NETIF_MSG_LINK 0x0004
69 2 NETIF_MSG_TIMER 0x0004
70 3 NETIF_MSG_IFDOWN 0x0008
71 3 NETIF_MSG_IFUP 0x0008
72 4 NETIF_MSG_RX_ERR 0x0010
73 4 NETIF_MSG_TX_ERR 0x0010
74 5 NETIF_MSG_TX_QUEUED 0x0020
75 5 NETIF_MSG_INTR 0x0020
76 6 NETIF_MSG_TX_DONE 0x0040
77 6 NETIF_MSG_RX_STATUS 0x0040
78 7 NETIF_MSG_PKTDATA 0x0080
79