docs: networking: convert netif-msg.txt to ReST
- add SPDX header;
- adjust title and chapter markups;
- mark lists as such;
- mark code blocks and literals as such;
- adjust identation, whitespaces and blank lines;
- add to networking/index.rst.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/Documentation/networking/netif-msg.rst b/Documentation/networking/netif-msg.rst
new file mode 100644
index 0000000..b20d265
--- /dev/null
+++ b/Documentation/networking/netif-msg.rst
@@ -0,0 +1,95 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===============
+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
+ ========= =================== ============