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Diffstat (limited to 'Documentation/networking/netif-msg.txt')
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diff --git a/Documentation/networking/netif-msg.txt b/Documentation/networking/netif-msg.txt new file mode 100644 index 000000000000..18ad4cea6259 --- /dev/null +++ b/Documentation/networking/netif-msg.txt @@ -0,0 +1,79 @@ + +________________ +NETIF Msg Level + +The design of the network interface message level setting. + +History + + The design of the debugging message interface was guided and + constrained by backwards compatibility previous practice. It is useful + to understand the history and evolution in order to understand current + practice and relate it to older driver source code. + + From the beginning of Linux, each network device driver has had a local + integer variable that controls the debug message level. The message + level ranged from 0 to 7, and monotonically increased in verbosity. + + The message level was not precisely defined past level 3, but were + always implemented within +-1 of the specified level. Drivers tended + to shed the more verbose level messages as they matured. + 0 Minimal messages, only essential information on fatal errors. + 1 Standard messages, initialization status. No run-time messages + 2 Special media selection messages, generally timer-driver. + 3 Interface starts and stops, including normal status messages + 4 Tx and Rx frame error messages, and abnormal driver operation + 5 Tx packet queue information, interrupt events. + 6 Status on each completed Tx packet and received Rx packets + 7 Initial contents of Tx and Rx packets + + Initially this message level variable was uniquely named in each driver + e.g. "lance_debug", so that a kernel symbolic debugger could locate and + modify the setting. When kernel modules became common, the variables + were consistently renamed to "debug" and allowed to be set as a module + parameter. + + This approach worked well. However there is always a demand for + additional features. Over the years the following emerged as + reasonable and easily implemented enhancements + Using an ioctl() call to modify the level. + Per-interface rather than per-driver message level setting. + More selective control over the type of messages emitted. + + The netif_msg recommandation adds these features with only a minor + complexity and code size increase. + + The recommendation is the following points + Retaining the per-driver integer variable "debug" as a module + parameter with a default level of '1'. + + Adding a per-interface private variable named "msg_enable". The + variable is a bit map rather than a level, and is initialized as + 1 << debug + Or more precisely + debug < 0 ? 0 : 1 << min(sizeof(int)-1, debug) + + Messages should changes from + if (debug > 1) + printk(MSG_DEBUG "%s: ... + to + if (np->msg_enable & NETIF_MSG_LINK) + printk(MSG_DEBUG "%s: ... + + +The set of message levels is named + Old level Name Bit position + 0 NETIF_MSG_DRV 0x0001 + 1 NETIF_MSG_PROBE 0x0002 + 2 NETIF_MSG_LINK 0x0004 + 2 NETIF_MSG_TIMER 0x0004 + 3 NETIF_MSG_IFDOWN 0x0008 + 3 NETIF_MSG_IFUP 0x0008 + 4 NETIF_MSG_RX_ERR 0x0010 + 4 NETIF_MSG_TX_ERR 0x0010 + 5 NETIF_MSG_TX_QUEUED 0x0020 + 5 NETIF_MSG_INTR 0x0020 + 6 NETIF_MSG_TX_DONE 0x0040 + 6 NETIF_MSG_RX_STATUS 0x0040 + 7 NETIF_MSG_PKTDATA 0x0080 + |