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-
-________________
-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 recommendation 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
-