pr_debug、dev_dbg等动态调试三
內核版本：Linux-3.14
作者：彭東林
郵箱：pengdonglin137@163.com
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如果沒有使用CONFIG_DYNAMIC_DEBUG，那么就需要定義DEBUG，那么此時pr_debug就退化為了printk。
如果定義了CONFIG_DYNAMIC_DEBUG，下面有幾種方法：
參考內核文檔：Documentation/dynamic-debug-howto.txt
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Introduction
============
This document describes how to use the dynamic debug (dyndbg) feature.
Dynamic debug is designed to allow you to dynamically enable/disable
kernel code to obtain additional kernel information.? Currently, if
CONFIG_DYNAMIC_DEBUG is set, then all pr_debug()/dev_dbg() and
print_hex_dump_debug()/print_hex_dump_bytes() calls can be dynamically
enabled per-callsite.
If CONFIG_DYNAMIC_DEBUG is not set, print_hex_dump_debug() is just
shortcut for print_hex_dump(KERN_DEBUG).
For print_hex_dump_debug()/print_hex_dump_bytes(), format string is
its 'prefix_str' argument, if it is constant string; or "hexdump"
in case 'prefix_str' is build dynamically.
Dynamic debug has even more useful features:
* Simple query language allows turning on and off debugging
?? statements by matching any combination of 0 or 1 of:
?? - source filename
?? - function name
?? - line number (including ranges of line numbers)
?? - module name
?? - format string
* Provides a debugfs control file: <debugfs>/dynamic_debug/control
?? which can be read to display the complete list of known debug
?? statements, to help guide you
Controlling dynamic debug Behaviour
===================================
The behaviour of pr_debug()/dev_dbg()s are controlled via writing to a
control file in the 'debugfs' filesystem. Thus, you must first mount
the debugfs filesystem, in order to make use of this feature.
Subsequently, we refer to the control file as:
<debugfs>/dynamic_debug/control. For example, if you want to enable
printing from source file 'svcsock.c', line 1603 you simply do:
If you make a mistake with the syntax, the write will fail thus:
1: nullarbor:~ # echo 'file svcsock.c wtf 1 +p' > 2: <debugfs>/dynamic_debug/control 3: -bash: echo: write error: Invalid argumentViewing Dynamic Debug Behaviour
===========================
You can view the currently configured behaviour of all the debug
statements via:
You can also apply standard Unix text manipulation filters to this
data, e.g.
The third column shows the currently enabled flags for each debug
statement callsite (see below for definitions of the flags).? The
default value, with no flags enabled, is "=_".? So you can view all
the debug statement callsites with any non-default flags:
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Command Language Reference
==========================
At the lexical level, a command comprises a sequence of words separated
by spaces or tabs.? So these are all equivalent:
Command submissions are bounded by a write() system call.
Multiple commands can be written together, separated by ';' or '\n'.
If your query set is big, you can batch them too:
1: ~# cat query-batch-file > <debugfs>/dynamic_debug/controlA another way is to use wildcard. The match rule support '*' (matches
zero or more characters) and '?' (matches exactly one character).For
example, you can match all usb drivers:
At the syntactical level, a command comprises a sequence of match
specifications, followed by a flags change specification.
The match-spec's are used to choose a subset of the known pr_debug()
callsites to which to apply the flags-spec.? Think of them as a query
with implicit ANDs between each pair.? Note that an empty list of
match-specs will select all debug statement callsites.
A match specification comprises a keyword, which controls the
attribute of the callsite to be compared, and a value to compare
against.? Possible keywords are:
// Note: line-range cannot contain space, e.g.
// "1-30" is valid range but "1 - 30" is not.
lineno ::= unsigned-int
The meanings of each keyword are:
func
??? The given string is compared against the function name
??? of each callsite.? Example:
file
??? The given string is compared against either the full pathname, the
??? src-root relative pathname, or the basename of the source file of
??? each callsite.? Examples:
module
??? The given string is compared against the module name
??? of each callsite.? The module name is the string as
??? seen in "lsmod", i.e. without the directory or the .ko
??? suffix and with '-' changed to '_'.? Examples:
format
??? The given string is searched for in the dynamic debug format
??? string.? Note that the string does not need to match the
??? entire format, only some part.? Whitespace and other
??? special characters can be escaped using C octal character
??? escape \ooo notation, e.g. the space character is \040.
??? Alternatively, the string can be enclosed in double quote
??? characters (") or single quote characters (').
??? Examples:
line
??? The given line number or range of line numbers is compared
??? against the line number of each pr_debug() callsite.? A single
??? line number matches the callsite line number exactly.? A
??? range of line numbers matches any callsite between the first
??? and last line number inclusive.? An empty first number means
??? the first line in the file, an empty line number means the
??? last number in the file.? Examples:
The flags specification comprises a change operation followed
by one or more flag characters.? The change operation is one
of the characters:
The flags are:
1: p enables the pr_debug() callsite. 2: f Include the function name in the printed message 3: l Include line number in the printed message 4: m Include module name in the printed message 5: t Include thread ID in messages not generated from interrupt context 6: _ No flags are set. (Or'd with others on input)For print_hex_dump_debug() and print_hex_dump_bytes(), only 'p' flag
have meaning, other flags ignored.
For display, the flags are preceded by '='
(mnemonic: what the flags are currently equal to).
Note the regexp ^[-+=][flmpt_]+$ matches a flags specification.
To clear all flags at once, use "=_" or "-flmpt".
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Debug messages during Boot Process
==================================
To activate debug messages for core code and built-in modules during
the boot process, even before userspace and debugfs exists, use
dyndbg="QUERY", module.dyndbg="QUERY", or ddebug_query="QUERY"
(ddebug_query is obsoleted by dyndbg, and deprecated).? QUERY follows
the syntax described above, but must not exceed 1023 characters.? Your
bootloader may impose lower limits.
These dyndbg params are processed just after the ddebug tables are
processed, as part of the arch_initcall.? Thus you can enable debug
messages in all code run after this arch_initcall via this boot
parameter.
On an x86 system for example ACPI enablement is a subsys_initcall and
??
your machine (typically a laptop) has an Embedded Controller.
PCI (or other devices) initialization also is a hot candidate for using
this boot parameter for debugging purposes.
If foo module is not built-in, foo.dyndbg will still be processed at
boot time, without effect, but will be reprocessed when module is
loaded later.? dyndbg_query= and bare dyndbg= are only processed at
boot.
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Debug Messages at Module Initialization Time
============================================
When "modprobe foo" is called, modprobe scans /proc/cmdline for
foo.params, strips "foo.", and passes them to the kernel along with
params given in modprobe args or /etc/modprob.d/*.conf files,
in the following order:
1. # parameters given via /etc/modprobe.d/*.conf
1: options foo dyndbg=+pt 2: options foo dyndbg # defaults to +p2. # foo.dyndbg as given in boot args, "foo." is stripped and passed
??
3. # args to modprobe
??
These dyndbg queries are applied in order, with last having final say.
This allows boot args to override or modify those from /etc/modprobe.d
(sensible, since 1 is system wide, 2 is kernel or boot specific), and
modprobe args to override both.
In the foo.dyndbg="QUERY" form, the query must exclude "module foo".
"foo" is extracted from the param-name, and applied to each query in
"QUERY", and only 1 match-spec of each type is allowed.
The dyndbg option is a "fake" module parameter, which means:
- modules do not need to define it explicitly
- every module gets it tacitly, whether they use pr_debug or not
- it doesn't appear in /sys/module/$module/parameters/
? To see it, grep the control file, or inspect /proc/cmdline.
For CONFIG_DYNAMIC_DEBUG kernels, any settings given at boot-time (or
enabled by -DDEBUG flag during compilation) can be disabled later via
the sysfs interface if the debug messages are no longer needed:
Examples
========
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完。
轉載于:https://www.cnblogs.com/pengdonglin137/p/4622460.html
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