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95 lines
3.3 KiB
95 lines
3.3 KiB
.. SPDX-License-Identifier: GPL-2.0 |
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=============== |
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NETIF Msg Level |
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=============== |
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The design of the network interface message level setting. |
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History |
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------- |
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The design of the debugging message interface was guided and |
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constrained by backwards compatibility previous practice. It is useful |
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to understand the history and evolution in order to understand current |
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practice and relate it to older driver source code. |
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From the beginning of Linux, each network device driver has had a local |
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integer variable that controls the debug message level. The message |
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level ranged from 0 to 7, and monotonically increased in verbosity. |
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The message level was not precisely defined past level 3, but were |
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always implemented within +-1 of the specified level. Drivers tended |
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to shed the more verbose level messages as they matured. |
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- 0 Minimal messages, only essential information on fatal errors. |
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- 1 Standard messages, initialization status. No run-time messages |
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- 2 Special media selection messages, generally timer-driver. |
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- 3 Interface starts and stops, including normal status messages |
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- 4 Tx and Rx frame error messages, and abnormal driver operation |
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- 5 Tx packet queue information, interrupt events. |
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- 6 Status on each completed Tx packet and received Rx packets |
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- 7 Initial contents of Tx and Rx packets |
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Initially this message level variable was uniquely named in each driver |
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e.g. "lance_debug", so that a kernel symbolic debugger could locate and |
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modify the setting. When kernel modules became common, the variables |
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were consistently renamed to "debug" and allowed to be set as a module |
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parameter. |
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This approach worked well. However there is always a demand for |
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additional features. Over the years the following emerged as |
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reasonable and easily implemented enhancements |
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- Using an ioctl() call to modify the level. |
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- Per-interface rather than per-driver message level setting. |
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- More selective control over the type of messages emitted. |
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The netif_msg recommendation adds these features with only a minor |
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complexity and code size increase. |
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The recommendation is the following points |
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- Retaining the per-driver integer variable "debug" as a module |
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parameter with a default level of '1'. |
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- Adding a per-interface private variable named "msg_enable". The |
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variable is a bit map rather than a level, and is initialized as:: |
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1 << debug |
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Or more precisely:: |
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debug < 0 ? 0 : 1 << min(sizeof(int)-1, debug) |
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Messages should changes from:: |
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if (debug > 1) |
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printk(MSG_DEBUG "%s: ... |
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to:: |
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if (np->msg_enable & NETIF_MSG_LINK) |
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printk(MSG_DEBUG "%s: ... |
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The set of message levels is named |
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========= =================== ============ |
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Old level Name Bit position |
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========= =================== ============ |
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0 NETIF_MSG_DRV 0x0001 |
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1 NETIF_MSG_PROBE 0x0002 |
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2 NETIF_MSG_LINK 0x0004 |
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2 NETIF_MSG_TIMER 0x0004 |
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3 NETIF_MSG_IFDOWN 0x0008 |
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3 NETIF_MSG_IFUP 0x0008 |
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4 NETIF_MSG_RX_ERR 0x0010 |
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4 NETIF_MSG_TX_ERR 0x0010 |
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5 NETIF_MSG_TX_QUEUED 0x0020 |
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5 NETIF_MSG_INTR 0x0020 |
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6 NETIF_MSG_TX_DONE 0x0040 |
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6 NETIF_MSG_RX_STATUS 0x0040 |
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7 NETIF_MSG_PKTDATA 0x0080 |
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========= =================== ============
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