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1
2Introduction
3============
4
5This document describes how to use the dynamic debug (dyndbg) feature.
6
7Dynamic debug is designed to allow you to dynamically enable/disable
8kernel code to obtain additional kernel information. Currently, if
9CONFIG_DYNAMIC_DEBUG is set, then all pr_debug()/dev_dbg() and
10print_hex_dump_debug()/print_hex_dump_bytes() calls can be dynamically
11enabled per-callsite.
12
13If CONFIG_DYNAMIC_DEBUG is not set, print_hex_dump_debug() is just
14shortcut for print_hex_dump(KERN_DEBUG).
15
16For print_hex_dump_debug()/print_hex_dump_bytes(), format string is
17its 'prefix_str' argument, if it is constant string; or "hexdump"
18in case 'prefix_str' is build dynamically.
19
20Dynamic debug has even more useful features:
21
22 * Simple query language allows turning on and off debugging
23 statements by matching any combination of 0 or 1 of:
24
25 - source filename
26 - function name
27 - line number (including ranges of line numbers)
28 - module name
29 - format string
30
31 * Provides a debugfs control file: <debugfs>/dynamic_debug/control
32 which can be read to display the complete list of known debug
33 statements, to help guide you
34
35Controlling dynamic debug Behaviour
36===================================
37
38The behaviour of pr_debug()/dev_dbg()s are controlled via writing to a
39control file in the 'debugfs' filesystem. Thus, you must first mount
40the debugfs filesystem, in order to make use of this feature.
41Subsequently, we refer to the control file as:
42<debugfs>/dynamic_debug/control. For example, if you want to enable
43printing from source file 'svcsock.c', line 1603 you simply do:
44
45nullarbor:~ # echo 'file svcsock.c line 1603 +p' >
46 <debugfs>/dynamic_debug/control
47
48If you make a mistake with the syntax, the write will fail thus:
49
50nullarbor:~ # echo 'file svcsock.c wtf 1 +p' >
51 <debugfs>/dynamic_debug/control
52-bash: echo: write error: Invalid argument
53
54Viewing Dynamic Debug Behaviour
55===========================
56
57You can view the currently configured behaviour of all the debug
58statements via:
59
60nullarbor:~ # cat <debugfs>/dynamic_debug/control
61# filename:lineno [module]function flags format
62/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"
63/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:341 [svcxprt_rdma]svc_rdma_init =_ "\011max_inline : %d\012"
64/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:340 [svcxprt_rdma]svc_rdma_init =_ "\011sq_depth : %d\012"
65/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:338 [svcxprt_rdma]svc_rdma_init =_ "\011max_requests : %d\012"
66...
67
68
69You can also apply standard Unix text manipulation filters to this
70data, e.g.
71
72nullarbor:~ # grep -i rdma <debugfs>/dynamic_debug/control | wc -l
7362
74
75nullarbor:~ # grep -i tcp <debugfs>/dynamic_debug/control | wc -l
7642
77
78The third column shows the currently enabled flags for each debug
79statement callsite (see below for definitions of the flags). The
80default value, with no flags enabled, is "=_". So you can view all
81the debug statement callsites with any non-default flags:
82
83nullarbor:~ # awk '$3 != "=_"' <debugfs>/dynamic_debug/control
84# filename:lineno [module]function flags format
85/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"
86
87
88Command Language Reference
89==========================
90
91At the lexical level, a command comprises a sequence of words separated
92by spaces or tabs. So these are all equivalent:
93
94nullarbor:~ # echo -c 'file svcsock.c line 1603 +p' >
95 <debugfs>/dynamic_debug/control
96nullarbor:~ # echo -c ' file svcsock.c line 1603 +p ' >
97 <debugfs>/dynamic_debug/control
98nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' >
99 <debugfs>/dynamic_debug/control
100
101Command submissions are bounded by a write() system call.
102Multiple commands can be written together, separated by ';' or '\n'.
103
104 ~# echo "func pnpacpi_get_resources +p; func pnp_assign_mem +p" \
105 > <debugfs>/dynamic_debug/control
106
107If your query set is big, you can batch them too:
108
109 ~# cat query-batch-file > <debugfs>/dynamic_debug/control
110
111A another way is to use wildcard. The match rule support '*' (matches
112zero or more characters) and '?' (matches exactly one character).For
113example, you can match all usb drivers:
114
115 ~# echo "file drivers/usb/* +p" > <debugfs>/dynamic_debug/control
116
117At the syntactical level, a command comprises a sequence of match
118specifications, followed by a flags change specification.
119
120command ::= match-spec* flags-spec
121
122The match-spec's are used to choose a subset of the known pr_debug()
123callsites to which to apply the flags-spec. Think of them as a query
124with implicit ANDs between each pair. Note that an empty list of
125match-specs will select all debug statement callsites.
126
127A match specification comprises a keyword, which controls the
128attribute of the callsite to be compared, and a value to compare
129against. Possible keywords are:
130
131match-spec ::= 'func' string |
132 'file' string |
133 'module' string |
134 'format' string |
135 'line' line-range
136
137line-range ::= lineno |
138 '-'lineno |
139 lineno'-' |
140 lineno'-'lineno
141// Note: line-range cannot contain space, e.g.
142// "1-30" is valid range but "1 - 30" is not.
143
144lineno ::= unsigned-int
145
146The meanings of each keyword are:
147
148func
149 The given string is compared against the function name
150 of each callsite. Example:
151
152 func svc_tcp_accept
153
154file
155 The given string is compared against either the full pathname, the
156 src-root relative pathname, or the basename of the source file of
157 each callsite. Examples:
158
159 file svcsock.c
160 file kernel/freezer.c
161 file /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svcsock.c
162
163module
164 The given string is compared against the module name
165 of each callsite. The module name is the string as
166 seen in "lsmod", i.e. without the directory or the .ko
167 suffix and with '-' changed to '_'. Examples:
168
169 module sunrpc
170 module nfsd
171
172format
173 The given string is searched for in the dynamic debug format
174 string. Note that the string does not need to match the
175 entire format, only some part. Whitespace and other
176 special characters can be escaped using C octal character
177 escape \ooo notation, e.g. the space character is \040.
178 Alternatively, the string can be enclosed in double quote
179 characters (") or single quote characters (').
180 Examples:
181
182 format svcrdma: // many of the NFS/RDMA server pr_debugs
183 format readahead // some pr_debugs in the readahead cache
184 format nfsd:\040SETATTR // one way to match a format with whitespace
185 format "nfsd: SETATTR" // a neater way to match a format with whitespace
186 format 'nfsd: SETATTR' // yet another way to match a format with whitespace
187
188line
189 The given line number or range of line numbers is compared
190 against the line number of each pr_debug() callsite. A single
191 line number matches the callsite line number exactly. A
192 range of line numbers matches any callsite between the first
193 and last line number inclusive. An empty first number means
194 the first line in the file, an empty line number means the
195 last number in the file. Examples:
196
197 line 1603 // exactly line 1603
198 line 1600-1605 // the six lines from line 1600 to line 1605
199 line -1605 // the 1605 lines from line 1 to line 1605
200 line 1600- // all lines from line 1600 to the end of the file
201
202The flags specification comprises a change operation followed
203by one or more flag characters. The change operation is one
204of the characters:
205
206 - remove the given flags
207 + add the given flags
208 = set the flags to the given flags
209
210The flags are:
211
212 p enables the pr_debug() callsite.
213 f Include the function name in the printed message
214 l Include line number in the printed message
215 m Include module name in the printed message
216 t Include thread ID in messages not generated from interrupt context
217 _ No flags are set. (Or'd with others on input)
218
219For print_hex_dump_debug() and print_hex_dump_bytes(), only 'p' flag
220have meaning, other flags ignored.
221
222For display, the flags are preceded by '='
223(mnemonic: what the flags are currently equal to).
224
225Note the regexp ^[-+=][flmpt_]+$ matches a flags specification.
226To clear all flags at once, use "=_" or "-flmpt".
227
228
229Debug messages during Boot Process
230==================================
231
232To activate debug messages for core code and built-in modules during
233the boot process, even before userspace and debugfs exists, use
234dyndbg="QUERY", module.dyndbg="QUERY", or ddebug_query="QUERY"
235(ddebug_query is obsoleted by dyndbg, and deprecated). QUERY follows
236the syntax described above, but must not exceed 1023 characters. Your
237bootloader may impose lower limits.
238
239These dyndbg params are processed just after the ddebug tables are
240processed, as part of the arch_initcall. Thus you can enable debug
241messages in all code run after this arch_initcall via this boot
242parameter.
243
244On an x86 system for example ACPI enablement is a subsys_initcall and
245 dyndbg="file ec.c +p"
246will show early Embedded Controller transactions during ACPI setup if
247your machine (typically a laptop) has an Embedded Controller.
248PCI (or other devices) initialization also is a hot candidate for using
249this boot parameter for debugging purposes.
250
251If foo module is not built-in, foo.dyndbg will still be processed at
252boot time, without effect, but will be reprocessed when module is
253loaded later. dyndbg_query= and bare dyndbg= are only processed at
254boot.
255
256
257Debug Messages at Module Initialization Time
258============================================
259
260When "modprobe foo" is called, modprobe scans /proc/cmdline for
261foo.params, strips "foo.", and passes them to the kernel along with
262params given in modprobe args or /etc/modprob.d/*.conf files,
263in the following order:
264
2651. # parameters given via /etc/modprobe.d/*.conf
266 options foo dyndbg=+pt
267 options foo dyndbg # defaults to +p
268
2692. # foo.dyndbg as given in boot args, "foo." is stripped and passed
270 foo.dyndbg=" func bar +p; func buz +mp"
271
2723. # args to modprobe
273 modprobe foo dyndbg==pmf # override previous settings
274
275These dyndbg queries are applied in order, with last having final say.
276This allows boot args to override or modify those from /etc/modprobe.d
277(sensible, since 1 is system wide, 2 is kernel or boot specific), and
278modprobe args to override both.
279
280In the foo.dyndbg="QUERY" form, the query must exclude "module foo".
281"foo" is extracted from the param-name, and applied to each query in
282"QUERY", and only 1 match-spec of each type is allowed.
283
284The dyndbg option is a "fake" module parameter, which means:
285
286- modules do not need to define it explicitly
287- every module gets it tacitly, whether they use pr_debug or not
288- it doesn't appear in /sys/module/$module/parameters/
289 To see it, grep the control file, or inspect /proc/cmdline.
290
291For CONFIG_DYNAMIC_DEBUG kernels, any settings given at boot-time (or
292enabled by -DDEBUG flag during compilation) can be disabled later via
293the sysfs interface if the debug messages are no longer needed:
294
295 echo "module module_name -p" > <debugfs>/dynamic_debug/control
296
297Examples
298========
299
300// enable the message at line 1603 of file svcsock.c
301nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' >
302 <debugfs>/dynamic_debug/control
303
304// enable all the messages in file svcsock.c
305nullarbor:~ # echo -n 'file svcsock.c +p' >
306 <debugfs>/dynamic_debug/control
307
308// enable all the messages in the NFS server module
309nullarbor:~ # echo -n 'module nfsd +p' >
310 <debugfs>/dynamic_debug/control
311
312// enable all 12 messages in the function svc_process()
313nullarbor:~ # echo -n 'func svc_process +p' >
314 <debugfs>/dynamic_debug/control
315
316// disable all 12 messages in the function svc_process()
317nullarbor:~ # echo -n 'func svc_process -p' >
318 <debugfs>/dynamic_debug/control
319
320// enable messages for NFS calls READ, READLINK, READDIR and READDIR+.
321nullarbor:~ # echo -n 'format "nfsd: READ" +p' >
322 <debugfs>/dynamic_debug/control
323
324// enable messages in files of which the pathes include string "usb"
325nullarbor:~ # echo -n '*usb* +p' > <debugfs>/dynamic_debug/control
326
327// enable all messages
328nullarbor:~ # echo -n '+p' > <debugfs>/dynamic_debug/control
329
330// add module, function to all enabled messages
331nullarbor:~ # echo -n '+mf' > <debugfs>/dynamic_debug/control
332
333// boot-args example, with newlines and comments for readability
334Kernel command line: ...
335 // see whats going on in dyndbg=value processing
336 dynamic_debug.verbose=1
337 // enable pr_debugs in 2 builtins, #cmt is stripped
338 dyndbg="module params +p #cmt ; module sys +p"
339 // enable pr_debugs in 2 functions in a module loaded later
340 pc87360.dyndbg="func pc87360_init_device +p; func pc87360_find +p"
1
2Introduction
3============
4
5This document describes how to use the dynamic debug (ddebug) feature.
6
7Dynamic debug is designed to allow you to dynamically enable/disable kernel
8code to obtain additional kernel information. Currently, if
9CONFIG_DYNAMIC_DEBUG is set, then all pr_debug()/dev_dbg() calls can be
10dynamically enabled per-callsite.
11
12Dynamic 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
26Controlling dynamic debug Behaviour
27===================================
28
29The behaviour of pr_debug()/dev_dbg()s are controlled via writing to a
30control file in the 'debugfs' filesystem. Thus, you must first mount the debugfs
31filesystem, in order to make use of this feature. Subsequently, we refer to the
32control file as: <debugfs>/dynamic_debug/control. For example, if you want to
33enable printing from source file 'svcsock.c', line 1603 you simply do:
34
35nullarbor:~ # echo 'file svcsock.c line 1603 +p' >
36 <debugfs>/dynamic_debug/control
37
38If you make a mistake with the syntax, the write will fail thus:
39
40nullarbor:~ # echo 'file svcsock.c wtf 1 +p' >
41 <debugfs>/dynamic_debug/control
42-bash: echo: write error: Invalid argument
43
44Viewing Dynamic Debug Behaviour
45===========================
46
47You can view the currently configured behaviour of all the debug statements
48via:
49
50nullarbor:~ # 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 Module Removed, deregister RPC RDMA transport\012"
53/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:341 [svcxprt_rdma]svc_rdma_init - "\011max_inline : %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 : %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 : %d\012"
56...
57
58
59You can also apply standard Unix text manipulation filters to this
60data, e.g.
61
62nullarbor:~ # grep -i rdma <debugfs>/dynamic_debug/control | wc -l
6362
64
65nullarbor:~ # grep -i tcp <debugfs>/dynamic_debug/control | wc -l
6642
67
68Note in particular that the third column shows the enabled behaviour
69flags for each debug statement callsite (see below for definitions of the
70flags). The default value, no extra behaviour enabled, is "-". So
71you can view all the debug statement callsites with any non-default flags:
72
73nullarbor:~ # 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: st_sendto returned %d\012"
76
77
78Command Language Reference
79==========================
80
81At the lexical level, a command comprises a sequence of words separated
82by whitespace characters. Note that newlines are treated as word
83separators and do *not* end a command or allow multiple commands to
84be done together. So these are all equivalent:
85
86nullarbor:~ # echo -c 'file svcsock.c line 1603 +p' >
87 <debugfs>/dynamic_debug/control
88nullarbor:~ # echo -c ' file svcsock.c line 1603 +p ' >
89 <debugfs>/dynamic_debug/control
90nullarbor:~ # echo -c 'file svcsock.c\nline 1603 +p' >
91 <debugfs>/dynamic_debug/control
92nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' >
93 <debugfs>/dynamic_debug/control
94
95Commands are bounded by a write() system call. If you want to do
96multiple commands you need to do a separate "echo" for each, like:
97
98nullarbor:~ # echo 'file svcsock.c line 1603 +p' > /proc/dprintk ;\
99> echo 'file svcsock.c line 1563 +p' > /proc/dprintk
100
101or even like:
102
103nullarbor:~ # (
104> echo 'file svcsock.c line 1603 +p' ;\
105> echo 'file svcsock.c line 1563 +p' ;\
106> ) > /proc/dprintk
107
108At the syntactical level, a command comprises a sequence of match
109specifications, followed by a flags change specification.
110
111command ::= match-spec* flags-spec
112
113The match-spec's are used to choose a subset of the known dprintk()
114callsites to which to apply the flags-spec. Think of them as a query
115with implicit ANDs between each pair. Note that an empty list of
116match-specs is possible, but is not very useful because it will not
117match any debug statement callsites.
118
119A match specification comprises a keyword, which controls the attribute
120of the callsite to be compared, and a value to compare against. Possible
121keywords are:
122
123match-spec ::= 'func' string |
124 'file' string |
125 'module' string |
126 'format' string |
127 'line' line-range
128
129line-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
136lineno ::= unsigned-int
137
138The meanings of each keyword are:
139
140func
141 The given string is compared against the function name
142 of each callsite. Example:
143
144 func svc_tcp_accept
145
146file
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
154module
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
163format
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 Alternatively, the string can be enclosed in double quote
170 characters (") or single quote characters (').
171 Examples:
172
173 format svcrdma: // many of the NFS/RDMA server dprintks
174 format readahead // some dprintks in the readahead cache
175 format nfsd:\040SETATTR // one way to match a format with whitespace
176 format "nfsd: SETATTR" // a neater way to match a format with whitespace
177 format 'nfsd: SETATTR' // yet another way to match a format with whitespace
178
179line
180 The given line number or range of line numbers is compared
181 against the line number of each dprintk() callsite. A single
182 line number matches the callsite line number exactly. A
183 range of line numbers matches any callsite between the first
184 and last line number inclusive. An empty first number means
185 the first line in the file, an empty line number means the
186 last number in the file. Examples:
187
188 line 1603 // exactly line 1603
189 line 1600-1605 // the six lines from line 1600 to line 1605
190 line -1605 // the 1605 lines from line 1 to line 1605
191 line 1600- // all lines from line 1600 to the end of the file
192
193The flags specification comprises a change operation followed
194by one or more flag characters. The change operation is one
195of the characters:
196
197-
198 remove the given flags
199
200+
201 add the given flags
202
203=
204 set the flags to the given flags
205
206The flags are:
207
208f
209 Include the function name in the printed message
210l
211 Include line number in the printed message
212m
213 Include module name in the printed message
214p
215 Causes a printk() message to be emitted to dmesg
216t
217 Include thread ID in messages not generated from interrupt context
218
219Note the regexp ^[-+=][flmpt]+$ matches a flags specification.
220Note also that there is no convenient syntax to remove all
221the flags at once, you need to use "-flmpt".
222
223
224Debug messages during boot process
225==================================
226
227To be able to activate debug messages during the boot process,
228even before userspace and debugfs exists, use the boot parameter:
229ddebug_query="QUERY"
230
231QUERY follows the syntax described above, but must not exceed 1023
232characters. The enablement of debug messages is done as an arch_initcall.
233Thus you can enable debug messages in all code processed after this
234arch_initcall via this boot parameter.
235On an x86 system for example ACPI enablement is a subsys_initcall and
236ddebug_query="file ec.c +p"
237will show early Embedded Controller transactions during ACPI setup if
238your machine (typically a laptop) has an Embedded Controller.
239PCI (or other devices) initialization also is a hot candidate for using
240this boot parameter for debugging purposes.
241
242
243Examples
244========
245
246// enable the message at line 1603 of file svcsock.c
247nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' >
248 <debugfs>/dynamic_debug/control
249
250// enable all the messages in file svcsock.c
251nullarbor:~ # echo -n 'file svcsock.c +p' >
252 <debugfs>/dynamic_debug/control
253
254// enable all the messages in the NFS server module
255nullarbor:~ # echo -n 'module nfsd +p' >
256 <debugfs>/dynamic_debug/control
257
258// enable all 12 messages in the function svc_process()
259nullarbor:~ # echo -n 'func svc_process +p' >
260 <debugfs>/dynamic_debug/control
261
262// disable all 12 messages in the function svc_process()
263nullarbor:~ # echo -n 'func svc_process -p' >
264 <debugfs>/dynamic_debug/control
265
266// enable messages for NFS calls READ, READLINK, READDIR and READDIR+.
267nullarbor:~ # echo -n 'format "nfsd: READ" +p' >
268 <debugfs>/dynamic_debug/control