1.. SPDX-License-Identifier: GPL-2.0 2 3=============== 4NETIF Msg Level 5=============== 6 7The design of the network interface message level setting. 8 9History 10------- 11 12 The design of the debugging message interface was guided and 13 constrained by backwards compatibility previous practice. It is useful 14 to understand the history and evolution in order to understand current 15 practice and relate it to older driver source code. 16 17 From the beginning of Linux, each network device driver has had a local 18 integer variable that controls the debug message level. The message 19 level ranged from 0 to 7, and monotonically increased in verbosity. 20 21 The message level was not precisely defined past level 3, but were 22 always implemented within +-1 of the specified level. Drivers tended 23 to shed the more verbose level messages as they matured. 24 25 - 0 Minimal messages, only essential information on fatal errors. 26 - 1 Standard messages, initialization status. No run-time messages 27 - 2 Special media selection messages, generally timer-driver. 28 - 3 Interface starts and stops, including normal status messages 29 - 4 Tx and Rx frame error messages, and abnormal driver operation 30 - 5 Tx packet queue information, interrupt events. 31 - 6 Status on each completed Tx packet and received Rx packets 32 - 7 Initial contents of Tx and Rx packets 33 34 Initially this message level variable was uniquely named in each driver 35 e.g. "lance_debug", so that a kernel symbolic debugger could locate and 36 modify the setting. When kernel modules became common, the variables 37 were consistently renamed to "debug" and allowed to be set as a module 38 parameter. 39 40 This approach worked well. However there is always a demand for 41 additional features. Over the years the following emerged as 42 reasonable and easily implemented enhancements 43 44 - Using an ioctl() call to modify the level. 45 - Per-interface rather than per-driver message level setting. 46 - More selective control over the type of messages emitted. 47 48 The netif_msg recommendation adds these features with only a minor 49 complexity and code size increase. 50 51 The recommendation is the following points 52 53 - Retaining the per-driver integer variable "debug" as a module 54 parameter with a default level of '1'. 55 56 - Adding a per-interface private variable named "msg_enable". The 57 variable is a bit map rather than a level, and is initialized as:: 58 59 1 << debug 60 61 Or more precisely:: 62 63 debug < 0 ? 0 : 1 << min(sizeof(int)-1, debug) 64 65 Messages should changes from:: 66 67 if (debug > 1) 68 printk(MSG_DEBUG "%s: ... 69 70 to:: 71 72 if (np->msg_enable & NETIF_MSG_LINK) 73 printk(MSG_DEBUG "%s: ... 74 75 76The set of message levels is named 77 78 79 ========= =================== ============ 80 Old level Name Bit position 81 ========= =================== ============ 82 0 NETIF_MSG_DRV 0x0001 83 1 NETIF_MSG_PROBE 0x0002 84 2 NETIF_MSG_LINK 0x0004 85 2 NETIF_MSG_TIMER 0x0004 86 3 NETIF_MSG_IFDOWN 0x0008 87 3 NETIF_MSG_IFUP 0x0008 88 4 NETIF_MSG_RX_ERR 0x0010 89 4 NETIF_MSG_TX_ERR 0x0010 90 5 NETIF_MSG_TX_QUEUED 0x0020 91 5 NETIF_MSG_INTR 0x0020 92 6 NETIF_MSG_TX_DONE 0x0040 93 6 NETIF_MSG_RX_STATUS 0x0040 94 7 NETIF_MSG_PKTDATA 0x0080 95 ========= =================== ============ 96