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| -rw-r--r-- | Documentation/dynamic-debug-howto.txt | 232 | ||||
| -rw-r--r-- | lib/Kconfig.debug | 72 |
2 files changed, 273 insertions, 31 deletions
diff --git a/Documentation/dynamic-debug-howto.txt b/Documentation/dynamic-debug-howto.txt new file mode 100644 index 000000000000..68394825e86b --- /dev/null +++ b/Documentation/dynamic-debug-howto.txt @@ -0,0 +1,232 @@ + +Introduction +============ + +This document describes how to use the dynamic debug (ddebug) 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_debug() calls can be +dynamically enabled per-callsite. + +Dynamic debug has even more useful features: + + * Simple query language allows turning on and off debugging statements by + matching any combination 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_debug()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: + +nullarbor:~ # echo 'file svcsock.c line 1603 +p' > + <debugfs>/dynamic_debug/control + +If you make a mistake with the syntax, the write will fail thus: + +nullarbor:~ # echo 'file svcsock.c wtf 1 +p' > + <debugfs>/dynamic_debug/control +-bash: echo: write error: Invalid argument + +Viewing Dynamic Debug Behaviour +=========================== + +You can view the currently configured behaviour of all the debug statements +via: + +nullarbor:~ # cat <debugfs>/dynamic_debug/control +# filename:lineno [module]function flags format +/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:323 [svcxprt_rdma]svc_rdma_cleanup - "SVCRDMA\040Module\040Removed,\040deregister\040RPC\040RDMA\040transport\012" +/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:341 [svcxprt_rdma]svc_rdma_init - "\011max_inline\040\040\040\040\040\040\040:\040%d\012" +/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:340 [svcxprt_rdma]svc_rdma_init - "\011sq_depth\040\040\040\040\040\040\040\040\040:\040%d\012" +/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:338 [svcxprt_rdma]svc_rdma_init - "\011max_requests\040\040\040\040\040:\040%d\012" +... + + +You can also apply standard Unix text manipulation filters to this +data, e.g. + +nullarbor:~ # grep -i rdma <debugfs>/dynamic_debug/control | wc -l +62 + +nullarbor:~ # grep -i tcp <debugfs>/dynamic_debug/control | wc -l +42 + +Note in particular that the third column shows the enabled behaviour +flags for each debug statement callsite (see below for definitions of the +flags). The default value, no extra behaviour enabled, is "-". So +you can view all the debug statement callsites with any non-default flags: + +nullarbor:~ # awk '$3 != "-"' <debugfs>/dynamic_debug/control +# filename:lineno [module]function flags format +/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svcsock.c:1603 [sunrpc]svc_send p "svc_process:\040st_sendto\040returned\040%d\012" + + +Command Language Reference +========================== + +At the lexical level, a command comprises a sequence of words separated +by whitespace characters. Note that newlines are treated as word +separators and do *not* end a command or allow multiple commands to +be done together. So these are all equivalent: + +nullarbor:~ # echo -c 'file svcsock.c line 1603 +p' > + <debugfs>/dynamic_debug/control +nullarbor:~ # echo -c ' file svcsock.c line 1603 +p ' > + <debugfs>/dynamic_debug/control +nullarbor:~ # echo -c 'file svcsock.c\nline 1603 +p' > + <debugfs>/dynamic_debug/control +nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' > + <debugfs>/dynamic_debug/control + +Commands are bounded by a write() system call. If you want to do +multiple commands you need to do a separate "echo" for each, like: + +nullarbor:~ # echo 'file svcsock.c line 1603 +p' > /proc/dprintk ;\ +> echo 'file svcsock.c line 1563 +p' > /proc/dprintk + +or even like: + +nullarbor:~ # ( +> echo 'file svcsock.c line 1603 +p' ;\ +> echo 'file svcsock.c line 1563 +p' ;\ +> ) > /proc/dprintk + +At the syntactical level, a command comprises a sequence of match +specifications, followed by a flags change specification. + +command ::= match-spec* flags-spec + +The match-spec's are used to choose a subset of the known dprintk() +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 is possible, but is not very useful because it will not +match any 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: + +match-spec ::= 'func' string | + 'file' string | + 'module' string | + 'format' string | + 'line' line-range + +line-range ::= lineno | + '-'lineno | + lineno'-' | + lineno'-'lineno +// 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: + + func svc_tcp_accept + +file + The given string is compared against either the full + pathname or the basename of the source file of each + callsite. Examples: + + file svcsock.c + file /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svcsock.c + +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: + + module sunrpc + module nfsd + +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. + Examples: + + format svcrdma: // many of the NFS/RDMA server dprintks + format readahead // some dprintks in the readahead cache + format nfsd:\040SETATTR // how to match a format with whitespace + +line + The given line number or range of line numbers is compared + against the line number of each dprintk() 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: + + line 1603 // exactly line 1603 + line 1600-1605 // the six lines from line 1600 to line 1605 + line -1605 // the 1605 lines from line 1 to line 1605 + line 1600- // all lines from line 1600 to the end of the file + +The flags specification comprises a change operation followed +by one or more flag characters. The change operation is one +of the characters: + +- + remove the given flags + ++ + add the given flags + += + set the flags to the given flags + +The flags are: + +p + Causes a printk() message to be emitted to dmesg + +Note the regexp ^[-+=][scp]+$ matches a flags specification. +Note also that there is no convenient syntax to remove all +the flags at once, you need to use "-psc". + +Examples +======== + +// enable the message at line 1603 of file svcsock.c +nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' > + <debugfs>/dynamic_debug/control + +// enable all the messages in file svcsock.c +nullarbor:~ # echo -n 'file svcsock.c +p' > + <debugfs>/dynamic_debug/control + +// enable all the messages in the NFS server module +nullarbor:~ # echo -n 'module nfsd +p' > + <debugfs>/dynamic_debug/control + +// enable all 12 messages in the function svc_process() +nullarbor:~ # echo -n 'func svc_process +p' > + <debugfs>/dynamic_debug/control + +// disable all 12 messages in the function svc_process() +nullarbor:~ # echo -n 'func svc_process -p' > + <debugfs>/dynamic_debug/control diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 0dd1c04c7323..8fee0a13ac58 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -848,59 +848,69 @@ config BUILD_DOCSRC Say N if you are unsure. config DYNAMIC_DEBUG - bool "Enable dynamic printk() call support" + bool "Enable dynamic printk() support" default n depends on PRINTK + depends on DEBUG_FS select PRINTK_DEBUG help Compiles debug level messages into the kernel, which would not otherwise be available at runtime. These messages can then be - enabled/disabled on a per module basis. This mechanism implicitly - enables all pr_debug() and dev_dbg() calls. The impact of this - compile option is a larger kernel text size of about 2%. + enabled/disabled based on various levels of scope - per source file, + function, module, format string, and line number. This mechanism + implicitly enables all pr_debug() and dev_dbg() calls. The impact of + this compile option is a larger kernel text size of about 2%. Usage: - Dynamic debugging is controlled by the debugfs file, - dynamic_printk/modules. This file contains a list of the modules that - can be enabled. The format of the file is the module name, followed - by a set of flags that can be enabled. The first flag is always the - 'enabled' flag. For example: + Dynamic debugging is controlled via the 'dynamic_debug/ddebug' file, + which is contained in the 'debugfs' filesystem. Thus, the debugfs + filesystem must first be mounted before making use of this feature. + We refer the control file as: <debugfs>/dynamic_debug/ddebug. This + file contains a list of the debug statements that can be enabled. The + format for each line of the file is: - <module_name> <enabled=0/1> - . - . - . + filename:lineno [module]function flags format - <module_name> : Name of the module in which the debug call resides - <enabled=0/1> : whether the messages are enabled or not + filename : source file of the debug statement + lineno : line number of the debug statement + module : module that contains the debug statement + function : function that contains the debug statement + flags : 'p' means the line is turned 'on' for printing + format : the format used for the debug statement From a live system: - snd_hda_intel enabled=0 - fixup enabled=0 - driver enabled=0 + nullarbor:~ # cat <debugfs>/dynamic_debug/ddebug + # filename:lineno [module]function flags format + fs/aio.c:222 [aio]__put_ioctx - "__put_ioctx:\040freeing\040%p\012" + fs/aio.c:248 [aio]ioctx_alloc - "ENOMEM:\040nr_events\040too\040high\012" + fs/aio.c:1770 [aio]sys_io_cancel - "calling\040cancel\012" - Enable a module: + Example usage: - $echo "set enabled=1 <module_name>" > dynamic_printk/modules + // enable the message at line 1603 of file svcsock.c + nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' > + <debugfs>/dynamic_debug/ddebug - Disable a module: + // enable all the messages in file svcsock.c + nullarbor:~ # echo -n 'file svcsock.c +p' > + <debugfs>/dynamic_debug/ddebug - $echo "set enabled=0 <module_name>" > dynamic_printk/modules + // enable all the messages in the NFS server module + nullarbor:~ # echo -n 'module nfsd +p' > + <debugfs>/dynamic_debug/ddebug - Enable all modules: + // enable all 12 messages in the function svc_process() + nullarbor:~ # echo -n 'func svc_process +p' > + <debugfs>/dynamic_debug/ddebug - $echo "set enabled=1 all" > dynamic_printk/modules + // disable all 12 messages in the function svc_process() + nullarbor:~ # echo -n 'func svc_process -p' > + <debugfs>/dynamic_debug/ddebug - Disable all modules: - - $echo "set enabled=0 all" > dynamic_printk/modules - - Finally, passing "dynamic_printk" at the command line enables - debugging for all modules. This mode can be turned off via the above - disable command. + See Documentation/dynamic-debug-howto.txt for additional information. source "samples/Kconfig" |