dynamic debug: update docs

updates the documentation for 'dynamic debug' feature. Signed-off-by: Greg Banks <gnb@sgi.com> Signed-off-by: Jason Baron <jbaron@redhat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

dynamic debug: update docs
updates the documentation for 'dynamic debug' feature. Signed-off-by: Greg Banks <gnb@sgi.com> Signed-off-by: Jason Baron <jbaron@redhat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Jason Baron · Greg Kroah-Hartman
1 parent e9d376f0fa
Showing 2 changed files with 273 additions and 31 deletions Side-by-side Diff
Documentation/dynamic-debug-howto.txt
lib/Kconfig.debug
+
+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
@@ -848,59 +848,69 @@
 	  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"
	1	+
	2	+Introduction
	3	+============
	4	+
	5	+This document describes how to use the dynamic debug (ddebug) feature.
	6	+
	7	+Dynamic debug is designed to allow you to dynamically enable/disable kernel
	8	+code to obtain additional kernel information. Currently, if
	9	+CONFIG_DYNAMIC_DEBUG is set, then all pr_debug()/dev_debug() calls can be
	10	+dynamically enabled per-callsite.
	11	+
	12	+Dynamic debug has even more useful features:
	13	+
	14	+ * Simple query language allows turning on and off debugging statements by
	15	+ matching any combination of:
	16	+
	17	+ - source filename
	18	+ - function name
	19	+ - line number (including ranges of line numbers)
	20	+ - module name
	21	+ - format string
	22	+
	23	+ * Provides a debugfs control file: <debugfs>/dynamic_debug/control which can be
	24	+ read to display the complete list of known debug statements, to help guide you
	25	+
	26	+Controlling dynamic debug Behaviour
	27	+===============================
	28	+
	29	+The behaviour of pr_debug()/dev_debug()s are controlled via writing to a
	30	+control file in the 'debugfs' filesystem. Thus, you must first mount the debugfs
	31	+filesystem, in order to make use of this feature. Subsequently, we refer to the
	32	+control file as: <debugfs>/dynamic_debug/control. For example, if you want to
	33	+enable printing from source file 'svcsock.c', line 1603 you simply do:
	34	+
	35	+nullarbor:~ # echo 'file svcsock.c line 1603 +p' >
	36	+ <debugfs>/dynamic_debug/control
	37	+
	38	+If you make a mistake with the syntax, the write will fail thus:
	39	+
	40	+nullarbor:~ # echo 'file svcsock.c wtf 1 +p' >
	41	+ <debugfs>/dynamic_debug/control
	42	+-bash: echo: write error: Invalid argument
	43	+
	44	+Viewing Dynamic Debug Behaviour
	45	+===========================
	46	+
	47	+You can view the currently configured behaviour of all the debug statements
	48	+via:
	49	+
	50	+nullarbor:~ # cat <debugfs>/dynamic_debug/control
	51	+# filename:lineno [module]function flags format
	52	+/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"
	53	+/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"
	54	+/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"
	55	+/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"
	56	+...
	57	+
	58	+
	59	+You can also apply standard Unix text manipulation filters to this
	60	+data, e.g.
	61	+
	62	+nullarbor:~ # grep -i rdma <debugfs>/dynamic_debug/control \| wc -l
	63	+62
	64	+
	65	+nullarbor:~ # grep -i tcp <debugfs>/dynamic_debug/control \| wc -l
	66	+42
	67	+
	68	+Note in particular that the third column shows the enabled behaviour
	69	+flags for each debug statement callsite (see below for definitions of the
	70	+flags). The default value, no extra behaviour enabled, is "-". So
	71	+you can view all the debug statement callsites with any non-default flags:
	72	+
	73	+nullarbor:~ # awk '$3 != "-"' <debugfs>/dynamic_debug/control
	74	+# filename:lineno [module]function flags format
	75	+/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"
	76	+
	77	+
	78	+Command Language Reference
	79	+==========================
	80	+
	81	+At the lexical level, a command comprises a sequence of words separated
	82	+by whitespace characters. Note that newlines are treated as word
	83	+separators and do not end a command or allow multiple commands to
	84	+be done together. So these are all equivalent:
	85	+
	86	+nullarbor:~ # echo -c 'file svcsock.c line 1603 +p' >
	87	+ <debugfs>/dynamic_debug/control
	88	+nullarbor:~ # echo -c ' file svcsock.c line 1603 +p ' >
	89	+ <debugfs>/dynamic_debug/control
	90	+nullarbor:~ # echo -c 'file svcsock.c\nline 1603 +p' >
	91	+ <debugfs>/dynamic_debug/control
	92	+nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' >
	93	+ <debugfs>/dynamic_debug/control
	94	+
	95	+Commands are bounded by a write() system call. If you want to do
	96	+multiple commands you need to do a separate "echo" for each, like:
	97	+
	98	+nullarbor:~ # echo 'file svcsock.c line 1603 +p' > /proc/dprintk ;\
	99	+> echo 'file svcsock.c line 1563 +p' > /proc/dprintk
	100	+
	101	+or even like:
	102	+
	103	+nullarbor:~ # (
	104	+> echo 'file svcsock.c line 1603 +p' ;\
	105	+> echo 'file svcsock.c line 1563 +p' ;\
	106	+> ) > /proc/dprintk
	107	+
	108	+At the syntactical level, a command comprises a sequence of match
	109	+specifications, followed by a flags change specification.
	110	+
	111	+command ::= match-spec* flags-spec
	112	+
	113	+The match-spec's are used to choose a subset of the known dprintk()
	114	+callsites to which to apply the flags-spec. Think of them as a query
	115	+with implicit ANDs between each pair. Note that an empty list of
	116	+match-specs is possible, but is not very useful because it will not
	117	+match any debug statement callsites.
	118	+
	119	+A match specification comprises a keyword, which controls the attribute
	120	+of the callsite to be compared, and a value to compare against. Possible
	121	+keywords are:
	122	+
	123	+match-spec ::= 'func' string \|
	124	+ 'file' string \|
	125	+ 'module' string \|
	126	+ 'format' string \|
	127	+ 'line' line-range
	128	+
	129	+line-range ::= lineno \|
	130	+ '-'lineno \|
	131	+ lineno'-' \|
	132	+ lineno'-'lineno
	133	+// Note: line-range cannot contain space, e.g.
	134	+// "1-30" is valid range but "1 - 30" is not.
	135	+
	136	+lineno ::= unsigned-int
	137	+
	138	+The meanings of each keyword are:
	139	+
	140	+func
	141	+ The given string is compared against the function name
	142	+ of each callsite. Example:
	143	+
	144	+ func svc_tcp_accept
	145	+
	146	+file
	147	+ The given string is compared against either the full
	148	+ pathname or the basename of the source file of each
	149	+ callsite. Examples:
	150	+
	151	+ file svcsock.c
	152	+ file /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svcsock.c
	153	+
	154	+module
	155	+ The given string is compared against the module name
	156	+ of each callsite. The module name is the string as
	157	+ seen in "lsmod", i.e. without the directory or the .ko
	158	+ suffix and with '-' changed to '_'. Examples:
	159	+
	160	+ module sunrpc
	161	+ module nfsd
	162	+
	163	+format
	164	+ The given string is searched for in the dynamic debug format
	165	+ string. Note that the string does not need to match the
	166	+ entire format, only some part. Whitespace and other
	167	+ special characters can be escaped using C octal character
	168	+ escape \ooo notation, e.g. the space character is \040.
	169	+ Examples:
	170	+
	171	+ format svcrdma: // many of the NFS/RDMA server dprintks
	172	+ format readahead // some dprintks in the readahead cache
	173	+ format nfsd:\040SETATTR // how to match a format with whitespace
	174	+
	175	+line
	176	+ The given line number or range of line numbers is compared
	177	+ against the line number of each dprintk() callsite. A single
	178	+ line number matches the callsite line number exactly. A
	179	+ range of line numbers matches any callsite between the first
	180	+ and last line number inclusive. An empty first number means
	181	+ the first line in the file, an empty line number means the
	182	+ last number in the file. Examples:
	183	+
	184	+ line 1603 // exactly line 1603
	185	+ line 1600-1605 // the six lines from line 1600 to line 1605
	186	+ line -1605 // the 1605 lines from line 1 to line 1605
	187	+ line 1600- // all lines from line 1600 to the end of the file
	188	+
	189	+The flags specification comprises a change operation followed
	190	+by one or more flag characters. The change operation is one
	191	+of the characters:
	192	+
	193	+-
	194	+ remove the given flags
	195	+
	196	++
	197	+ add the given flags
	198	+
	199	+=
	200	+ set the flags to the given flags
	201	+
	202	+The flags are:
	203	+
	204	+p
	205	+ Causes a printk() message to be emitted to dmesg
	206	+
	207	+Note the regexp ^[-+=][scp]+$ matches a flags specification.
	208	+Note also that there is no convenient syntax to remove all
	209	+the flags at once, you need to use "-psc".
	210	+
	211	+Examples
	212	+========
	213	+
	214	+// enable the message at line 1603 of file svcsock.c
	215	+nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' >
	216	+ <debugfs>/dynamic_debug/control
	217	+
	218	+// enable all the messages in file svcsock.c
	219	+nullarbor:~ # echo -n 'file svcsock.c +p' >
	220	+ <debugfs>/dynamic_debug/control
	221	+
	222	+// enable all the messages in the NFS server module
	223	+nullarbor:~ # echo -n 'module nfsd +p' >
	224	+ <debugfs>/dynamic_debug/control
	225	+
	226	+// enable all 12 messages in the function svc_process()
	227	+nullarbor:~ # echo -n 'func svc_process +p' >
	228	+ <debugfs>/dynamic_debug/control
	229	+
	230	+// disable all 12 messages in the function svc_process()
	231	+nullarbor:~ # echo -n 'func svc_process -p' >
	232	+ <debugfs>/dynamic_debug/control
...	...	@@ -848,59 +848,69 @@
848	848	Say N if you are unsure.
849	849
850	850	config DYNAMIC_DEBUG
851		- bool "Enable dynamic printk() call support"
	851	+ bool "Enable dynamic printk() support"
852	852	default n
853	853	depends on PRINTK
	854	+ depends on DEBUG_FS
854	855	select PRINTK_DEBUG
855	856	help
856	857
857	858	Compiles debug level messages into the kernel, which would not
858	859	otherwise be available at runtime. These messages can then be
859		- enabled/disabled on a per module basis. This mechanism implicitly
860		- enables all pr_debug() and dev_dbg() calls. The impact of this
861		- compile option is a larger kernel text size of about 2%.
	860	+ enabled/disabled based on various levels of scope - per source file,
	861	+ function, module, format string, and line number. This mechanism
	862	+ implicitly enables all pr_debug() and dev_dbg() calls. The impact of
	863	+ this compile option is a larger kernel text size of about 2%.
862	864
863	865	Usage:
864	866
865		- Dynamic debugging is controlled by the debugfs file,
866		- dynamic_printk/modules. This file contains a list of the modules that
867		- can be enabled. The format of the file is the module name, followed
868		- by a set of flags that can be enabled. The first flag is always the
869		- 'enabled' flag. For example:
	867	+ Dynamic debugging is controlled via the 'dynamic_debug/ddebug' file,
	868	+ which is contained in the 'debugfs' filesystem. Thus, the debugfs
	869	+ filesystem must first be mounted before making use of this feature.
	870	+ We refer the control file as: <debugfs>/dynamic_debug/ddebug. This
	871	+ file contains a list of the debug statements that can be enabled. The
	872	+ format for each line of the file is:
870	873
871		- <module_name> <enabled=0/1>
872		- .
873		- .
874		- .
	874	+ filename:lineno [module]function flags format
875	875
876		- <module_name> : Name of the module in which the debug call resides
877		- <enabled=0/1> : whether the messages are enabled or not
	876	+ filename : source file of the debug statement
	877	+ lineno : line number of the debug statement
	878	+ module : module that contains the debug statement
	879	+ function : function that contains the debug statement
	880	+ flags : 'p' means the line is turned 'on' for printing
	881	+ format : the format used for the debug statement
878	882
879	883	From a live system:
880	884
881		- snd_hda_intel enabled=0
882		- fixup enabled=0
883		- driver enabled=0
	885	+ nullarbor:~ # cat <debugfs>/dynamic_debug/ddebug
	886	+ # filename:lineno [module]function flags format
	887	+ fs/aio.c:222 [aio]__put_ioctx - "__put_ioctx:\040freeing\040%p\012"
	888	+ fs/aio.c:248 [aio]ioctx_alloc - "ENOMEM:\040nr_events\040too\040high\012"
	889	+ fs/aio.c:1770 [aio]sys_io_cancel - "calling\040cancel\012"
884	890
885		- Enable a module:
	891	+ Example usage:
886	892
887		- $echo "set enabled=1 <module_name>" > dynamic_printk/modules
	893	+ // enable the message at line 1603 of file svcsock.c
	894	+ nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' >
	895	+ <debugfs>/dynamic_debug/ddebug
888	896
889		- Disable a module:
	897	+ // enable all the messages in file svcsock.c
	898	+ nullarbor:~ # echo -n 'file svcsock.c +p' >
	899	+ <debugfs>/dynamic_debug/ddebug
890	900
891		- $echo "set enabled=0 <module_name>" > dynamic_printk/modules
	901	+ // enable all the messages in the NFS server module
	902	+ nullarbor:~ # echo -n 'module nfsd +p' >
	903	+ <debugfs>/dynamic_debug/ddebug
892	904
893		- Enable all modules:
	905	+ // enable all 12 messages in the function svc_process()
	906	+ nullarbor:~ # echo -n 'func svc_process +p' >
	907	+ <debugfs>/dynamic_debug/ddebug
894	908
895		- $echo "set enabled=1 all" > dynamic_printk/modules
	909	+ // disable all 12 messages in the function svc_process()
	910	+ nullarbor:~ # echo -n 'func svc_process -p' >
	911	+ <debugfs>/dynamic_debug/ddebug
896	912
897		- Disable all modules:
898		-
899		- $echo "set enabled=0 all" > dynamic_printk/modules
900		-
901		- Finally, passing "dynamic_printk" at the command line enables
902		- debugging for all modules. This mode can be turned off via the above
903		- disable command.
	913	+ See Documentation/dynamic-debug-howto.txt for additional information.
904	914
905	915	source "samples/Kconfig"
906	916