Documentation/dynamic-debug-howto.txt - kernel/msm-4.9 - Gitiles


 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 Module Removed, deregister RPC RDMA transport\012"
 /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:341 [svcxprt_rdma]svc_rdma_init - "\011max_inline       : %d\012"
 /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:340 [svcxprt_rdma]svc_rdma_init - "\011sq_depth         : %d\012"
 /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:338 [svcxprt_rdma]svc_rdma_init - "\011max_requests     : %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: st_sendto returned %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.
     Alternatively, the string can be enclosed in double quote
     characters (") or single quote characters (').
     Examples:

     format svcrdma:	    // many of the NFS/RDMA server dprintks
     format readahead	    // some dprintks in the readahead cache
     format nfsd:\040SETATTR // one way to match a format with whitespace
     format "nfsd: SETATTR"  // a neater way to match a format with whitespace
     format 'nfsd: SETATTR'  // yet another way 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".


 Debug messages during boot process
 ==================================

 To be able to activate debug messages during the boot process,
 even before userspace and debugfs exists, use the boot parameter:
 ddebug_query="QUERY"

 QUERY follows the syntax described above, but must not exceed 1023
 characters. The enablement of debug messages is done as an arch_initcall.
 Thus you can enable debug messages in all code processed after this
 arch_initcall via this boot parameter.
 On an x86 system for example ACPI enablement is a subsys_initcall and
 ddebug_query="file ec.c +p"
 will show early Embedded Controller transactions during ACPI setup if
 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.


 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

 // enable messages for NFS calls READ, READLINK, READDIR and READDIR+.
 nullarbor:~ # echo -n 'format "nfsd: READ" +p' >
 				<debugfs>/dynamic_debug/control

	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 Module Removed, deregister RPC RDMA transport\012"
	/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:341 [svcxprt_rdma]svc_rdma_init - "\011max_inline : %d\012"
	/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:340 [svcxprt_rdma]svc_rdma_init - "\011sq_depth : %d\012"
	/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:338 [svcxprt_rdma]svc_rdma_init - "\011max_requests : %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: st_sendto returned %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.
	Alternatively, the string can be enclosed in double quote
	characters (") or single quote characters (').
	Examples:

	format svcrdma: // many of the NFS/RDMA server dprintks
	format readahead // some dprintks in the readahead cache
	format nfsd:\040SETATTR // one way to match a format with whitespace
	format "nfsd: SETATTR" // a neater way to match a format with whitespace
	format 'nfsd: SETATTR' // yet another way 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".


	Debug messages during boot process
	==================================

	To be able to activate debug messages during the boot process,
	even before userspace and debugfs exists, use the boot parameter:
	ddebug_query="QUERY"

	QUERY follows the syntax described above, but must not exceed 1023
	characters. The enablement of debug messages is done as an arch_initcall.
	Thus you can enable debug messages in all code processed after this
	arch_initcall via this boot parameter.
	On an x86 system for example ACPI enablement is a subsys_initcall and
	ddebug_query="file ec.c +p"
	will show early Embedded Controller transactions during ACPI setup if
	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.


	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

	// enable messages for NFS calls READ, READLINK, READDIR and READDIR+.
	nullarbor:~ # echo -n 'format "nfsd: READ" +p' >
	<debugfs>/dynamic_debug/control