linux/Documentation/networking/netif-msg.txt
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   2________________
   3NETIF Msg Level
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   5The design of the network interface message level setting.
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   7History
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   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
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  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.
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  36 This approeachworkevelel v2.6.17.6