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1Dynamic debug
2+++++++++++++
3
4
5Introduction
6============
7
8This document describes how to use the dynamic debug (dyndbg) feature.
9
10Dynamic debug is designed to allow you to dynamically enable/disable
11kernel code to obtain additional kernel information. Currently, if
12``CONFIG_DYNAMIC_DEBUG`` is set, then all ``pr_debug()``/``dev_dbg()`` and
13``print_hex_dump_debug()``/``print_hex_dump_bytes()`` calls can be dynamically
14enabled per-callsite.
15
16If you do not want to enable dynamic debug globally (i.e. in some embedded
17system), you may set ``CONFIG_DYNAMIC_DEBUG_CORE`` as basic support of dynamic
18debug and add ``ccflags := -DDYNAMIC_DEBUG_MODULE`` into the Makefile of any
19modules which you'd like to dynamically debug later.
20
21If ``CONFIG_DYNAMIC_DEBUG`` is not set, ``print_hex_dump_debug()`` is just
22shortcut for ``print_hex_dump(KERN_DEBUG)``.
23
24For ``print_hex_dump_debug()``/``print_hex_dump_bytes()``, format string is
25its ``prefix_str`` argument, if it is constant string; or ``hexdump``
26in case ``prefix_str`` is built dynamically.
27
28Dynamic debug has even more useful features:
29
30 * Simple query language allows turning on and off debugging
31 statements by matching any combination of 0 or 1 of:
32
33 - source filename
34 - function name
35 - line number (including ranges of line numbers)
36 - module name
37 - format string
38
39 * Provides a debugfs control file: ``<debugfs>/dynamic_debug/control``
40 which can be read to display the complete list of known debug
41 statements, to help guide you
42
43Controlling dynamic debug Behaviour
44===================================
45
46The behaviour of ``pr_debug()``/``dev_dbg()`` are controlled via writing to a
47control file in the 'debugfs' filesystem. Thus, you must first mount
48the debugfs filesystem, in order to make use of this feature.
49Subsequently, we refer to the control file as:
50``<debugfs>/dynamic_debug/control``. For example, if you want to enable
51printing from source file ``svcsock.c``, line 1603 you simply do::
52
53 nullarbor:~ # echo 'file svcsock.c line 1603 +p' >
54 <debugfs>/dynamic_debug/control
55
56If you make a mistake with the syntax, the write will fail thus::
57
58 nullarbor:~ # echo 'file svcsock.c wtf 1 +p' >
59 <debugfs>/dynamic_debug/control
60 -bash: echo: write error: Invalid argument
61
62Note, for systems without 'debugfs' enabled, the control file can be
63found in ``/proc/dynamic_debug/control``.
64
65Viewing Dynamic Debug Behaviour
66===============================
67
68You can view the currently configured behaviour of all the debug
69statements via::
70
71 nullarbor:~ # cat <debugfs>/dynamic_debug/control
72 # filename:lineno [module]function flags format
73 net/sunrpc/svc_rdma.c:323 [svcxprt_rdma]svc_rdma_cleanup =_ "SVCRDMA Module Removed, deregister RPC RDMA transport\012"
74 net/sunrpc/svc_rdma.c:341 [svcxprt_rdma]svc_rdma_init =_ "\011max_inline : %d\012"
75 net/sunrpc/svc_rdma.c:340 [svcxprt_rdma]svc_rdma_init =_ "\011sq_depth : %d\012"
76 net/sunrpc/svc_rdma.c:338 [svcxprt_rdma]svc_rdma_init =_ "\011max_requests : %d\012"
77 ...
78
79
80You can also apply standard Unix text manipulation filters to this
81data, e.g.::
82
83 nullarbor:~ # grep -i rdma <debugfs>/dynamic_debug/control | wc -l
84 62
85
86 nullarbor:~ # grep -i tcp <debugfs>/dynamic_debug/control | wc -l
87 42
88
89The third column shows the currently enabled flags for each debug
90statement callsite (see below for definitions of the flags). The
91default value, with no flags enabled, is ``=_``. So you can view all
92the debug statement callsites with any non-default flags::
93
94 nullarbor:~ # awk '$3 != "=_"' <debugfs>/dynamic_debug/control
95 # filename:lineno [module]function flags format
96 net/sunrpc/svcsock.c:1603 [sunrpc]svc_send p "svc_process: st_sendto returned %d\012"
97
98Command Language Reference
99==========================
100
101At the lexical level, a command comprises a sequence of words separated
102by spaces or tabs. So these are all equivalent::
103
104 nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' >
105 <debugfs>/dynamic_debug/control
106 nullarbor:~ # echo -n ' file svcsock.c line 1603 +p ' >
107 <debugfs>/dynamic_debug/control
108 nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' >
109 <debugfs>/dynamic_debug/control
110
111Command submissions are bounded by a write() system call.
112Multiple commands can be written together, separated by ``;`` or ``\n``::
113
114 ~# echo "func pnpacpi_get_resources +p; func pnp_assign_mem +p" \
115 > <debugfs>/dynamic_debug/control
116
117If your query set is big, you can batch them too::
118
119 ~# cat query-batch-file > <debugfs>/dynamic_debug/control
120
121Another way is to use wildcards. The match rule supports ``*`` (matches
122zero or more characters) and ``?`` (matches exactly one character). For
123example, you can match all usb drivers::
124
125 ~# echo "file drivers/usb/* +p" > <debugfs>/dynamic_debug/control
126
127At the syntactical level, a command comprises a sequence of match
128specifications, followed by a flags change specification::
129
130 command ::= match-spec* flags-spec
131
132The match-spec's are used to choose a subset of the known pr_debug()
133callsites to which to apply the flags-spec. Think of them as a query
134with implicit ANDs between each pair. Note that an empty list of
135match-specs will select all debug statement callsites.
136
137A match specification comprises a keyword, which controls the
138attribute of the callsite to be compared, and a value to compare
139against. Possible keywords are:::
140
141 match-spec ::= 'func' string |
142 'file' string |
143 'module' string |
144 'format' string |
145 'line' line-range
146
147 line-range ::= lineno |
148 '-'lineno |
149 lineno'-' |
150 lineno'-'lineno
151
152 lineno ::= unsigned-int
153
154.. note::
155
156 ``line-range`` cannot contain space, e.g.
157 "1-30" is valid range but "1 - 30" is not.
158
159
160The meanings of each keyword are:
161
162func
163 The given string is compared against the function name
164 of each callsite. Example::
165
166 func svc_tcp_accept
167 func *recv* # in rfcomm, bluetooth, ping, tcp
168
169file
170 The given string is compared against either the src-root relative
171 pathname, or the basename of the source file of each callsite.
172 Examples::
173
174 file svcsock.c
175 file kernel/freezer.c # ie column 1 of control file
176 file drivers/usb/* # all callsites under it
177 file inode.c:start_* # parse :tail as a func (above)
178 file inode.c:1-100 # parse :tail as a line-range (above)
179
180module
181 The given string is compared against the module name
182 of each callsite. The module name is the string as
183 seen in ``lsmod``, i.e. without the directory or the ``.ko``
184 suffix and with ``-`` changed to ``_``. Examples::
185
186 module sunrpc
187 module nfsd
188 module drm* # both drm, drm_kms_helper
189
190format
191 The given string is searched for in the dynamic debug format
192 string. Note that the string does not need to match the
193 entire format, only some part. Whitespace and other
194 special characters can be escaped using C octal character
195 escape ``\ooo`` notation, e.g. the space character is ``\040``.
196 Alternatively, the string can be enclosed in double quote
197 characters (``"``) or single quote characters (``'``).
198 Examples::
199
200 format svcrdma: // many of the NFS/RDMA server pr_debugs
201 format readahead // some pr_debugs in the readahead cache
202 format nfsd:\040SETATTR // one way to match a format with whitespace
203 format "nfsd: SETATTR" // a neater way to match a format with whitespace
204 format 'nfsd: SETATTR' // yet another way to match a format with whitespace
205
206line
207 The given line number or range of line numbers is compared
208 against the line number of each ``pr_debug()`` callsite. A single
209 line number matches the callsite line number exactly. A
210 range of line numbers matches any callsite between the first
211 and last line number inclusive. An empty first number means
212 the first line in the file, an empty last line number means the
213 last line number in the file. Examples::
214
215 line 1603 // exactly line 1603
216 line 1600-1605 // the six lines from line 1600 to line 1605
217 line -1605 // the 1605 lines from line 1 to line 1605
218 line 1600- // all lines from line 1600 to the end of the file
219
220The flags specification comprises a change operation followed
221by one or more flag characters. The change operation is one
222of the characters::
223
224 - remove the given flags
225 + add the given flags
226 = set the flags to the given flags
227
228The flags are::
229
230 p enables the pr_debug() callsite.
231 f Include the function name in the printed message
232 l Include line number in the printed message
233 m Include module name in the printed message
234 t Include thread ID in messages not generated from interrupt context
235 _ No flags are set. (Or'd with others on input)
236
237For ``print_hex_dump_debug()`` and ``print_hex_dump_bytes()``, only ``p`` flag
238have meaning, other flags ignored.
239
240For display, the flags are preceded by ``=``
241(mnemonic: what the flags are currently equal to).
242
243Note the regexp ``^[-+=][flmpt_]+$`` matches a flags specification.
244To clear all flags at once, use ``=_`` or ``-flmpt``.
245
246
247Debug messages during Boot Process
248==================================
249
250To activate debug messages for core code and built-in modules during
251the boot process, even before userspace and debugfs exists, use
252``dyndbg="QUERY"``, ``module.dyndbg="QUERY"``, or ``ddebug_query="QUERY"``
253(``ddebug_query`` is obsoleted by ``dyndbg``, and deprecated). QUERY follows
254the syntax described above, but must not exceed 1023 characters. Your
255bootloader may impose lower limits.
256
257These ``dyndbg`` params are processed just after the ddebug tables are
258processed, as part of the early_initcall. Thus you can enable debug
259messages in all code run after this early_initcall via this boot
260parameter.
261
262On an x86 system for example ACPI enablement is a subsys_initcall and::
263
264 dyndbg="file ec.c +p"
265
266will show early Embedded Controller transactions during ACPI setup if
267your machine (typically a laptop) has an Embedded Controller.
268PCI (or other devices) initialization also is a hot candidate for using
269this boot parameter for debugging purposes.
270
271If ``foo`` module is not built-in, ``foo.dyndbg`` will still be processed at
272boot time, without effect, but will be reprocessed when module is
273loaded later. ``ddebug_query=`` and bare ``dyndbg=`` are only processed at
274boot.
275
276
277Debug Messages at Module Initialization Time
278============================================
279
280When ``modprobe foo`` is called, modprobe scans ``/proc/cmdline`` for
281``foo.params``, strips ``foo.``, and passes them to the kernel along with
282params given in modprobe args or ``/etc/modprob.d/*.conf`` files,
283in the following order:
284
2851. parameters given via ``/etc/modprobe.d/*.conf``::
286
287 options foo dyndbg=+pt
288 options foo dyndbg # defaults to +p
289
2902. ``foo.dyndbg`` as given in boot args, ``foo.`` is stripped and passed::
291
292 foo.dyndbg=" func bar +p; func buz +mp"
293
2943. args to modprobe::
295
296 modprobe foo dyndbg==pmf # override previous settings
297
298These ``dyndbg`` queries are applied in order, with last having final say.
299This allows boot args to override or modify those from ``/etc/modprobe.d``
300(sensible, since 1 is system wide, 2 is kernel or boot specific), and
301modprobe args to override both.
302
303In the ``foo.dyndbg="QUERY"`` form, the query must exclude ``module foo``.
304``foo`` is extracted from the param-name, and applied to each query in
305``QUERY``, and only 1 match-spec of each type is allowed.
306
307The ``dyndbg`` option is a "fake" module parameter, which means:
308
309- modules do not need to define it explicitly
310- every module gets it tacitly, whether they use pr_debug or not
311- it doesn't appear in ``/sys/module/$module/parameters/``
312 To see it, grep the control file, or inspect ``/proc/cmdline.``
313
314For ``CONFIG_DYNAMIC_DEBUG`` kernels, any settings given at boot-time (or
315enabled by ``-DDEBUG`` flag during compilation) can be disabled later via
316the debugfs interface if the debug messages are no longer needed::
317
318 echo "module module_name -p" > <debugfs>/dynamic_debug/control
319
320Examples
321========
322
323::
324
325 // enable the message at line 1603 of file svcsock.c
326 nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' >
327 <debugfs>/dynamic_debug/control
328
329 // enable all the messages in file svcsock.c
330 nullarbor:~ # echo -n 'file svcsock.c +p' >
331 <debugfs>/dynamic_debug/control
332
333 // enable all the messages in the NFS server module
334 nullarbor:~ # echo -n 'module nfsd +p' >
335 <debugfs>/dynamic_debug/control
336
337 // enable all 12 messages in the function svc_process()
338 nullarbor:~ # echo -n 'func svc_process +p' >
339 <debugfs>/dynamic_debug/control
340
341 // disable all 12 messages in the function svc_process()
342 nullarbor:~ # echo -n 'func svc_process -p' >
343 <debugfs>/dynamic_debug/control
344
345 // enable messages for NFS calls READ, READLINK, READDIR and READDIR+.
346 nullarbor:~ # echo -n 'format "nfsd: READ" +p' >
347 <debugfs>/dynamic_debug/control
348
349 // enable messages in files of which the paths include string "usb"
350 nullarbor:~ # echo -n 'file *usb* +p' > <debugfs>/dynamic_debug/control
351
352 // enable all messages
353 nullarbor:~ # echo -n '+p' > <debugfs>/dynamic_debug/control
354
355 // add module, function to all enabled messages
356 nullarbor:~ # echo -n '+mf' > <debugfs>/dynamic_debug/control
357
358 // boot-args example, with newlines and comments for readability
359 Kernel command line: ...
360 // see whats going on in dyndbg=value processing
361 dynamic_debug.verbose=1
362 // enable pr_debugs in 2 builtins, #cmt is stripped
363 dyndbg="module params +p #cmt ; module sys +p"
364 // enable pr_debugs in 2 functions in a module loaded later
365 pc87360.dyndbg="func pc87360_init_device +p; func pc87360_find +p"
1Dynamic debug
2+++++++++++++
3
4
5Introduction
6============
7
8This document describes how to use the dynamic debug (dyndbg) feature.
9
10Dynamic debug is designed to allow you to dynamically enable/disable
11kernel code to obtain additional kernel information. Currently, if
12``CONFIG_DYNAMIC_DEBUG`` is set, then all ``pr_debug()``/``dev_dbg()`` and
13``print_hex_dump_debug()``/``print_hex_dump_bytes()`` calls can be dynamically
14enabled per-callsite.
15
16If ``CONFIG_DYNAMIC_DEBUG`` is not set, ``print_hex_dump_debug()`` is just
17shortcut for ``print_hex_dump(KERN_DEBUG)``.
18
19For ``print_hex_dump_debug()``/``print_hex_dump_bytes()``, format string is
20its ``prefix_str`` argument, if it is constant string; or ``hexdump``
21in case ``prefix_str`` is built dynamically.
22
23Dynamic debug has even more useful features:
24
25 * Simple query language allows turning on and off debugging
26 statements by matching any combination of 0 or 1 of:
27
28 - source filename
29 - function name
30 - line number (including ranges of line numbers)
31 - module name
32 - format string
33
34 * Provides a debugfs control file: ``<debugfs>/dynamic_debug/control``
35 which can be read to display the complete list of known debug
36 statements, to help guide you
37
38Controlling dynamic debug Behaviour
39===================================
40
41The behaviour of ``pr_debug()``/``dev_dbg()`` are controlled via writing to a
42control file in the 'debugfs' filesystem. Thus, you must first mount
43the debugfs filesystem, in order to make use of this feature.
44Subsequently, we refer to the control file as:
45``<debugfs>/dynamic_debug/control``. For example, if you want to enable
46printing from source file ``svcsock.c``, line 1603 you simply do::
47
48 nullarbor:~ # echo 'file svcsock.c line 1603 +p' >
49 <debugfs>/dynamic_debug/control
50
51If you make a mistake with the syntax, the write will fail thus::
52
53 nullarbor:~ # echo 'file svcsock.c wtf 1 +p' >
54 <debugfs>/dynamic_debug/control
55 -bash: echo: write error: Invalid argument
56
57Viewing Dynamic Debug Behaviour
58===============================
59
60You can view the currently configured behaviour of all the debug
61statements via::
62
63 nullarbor:~ # cat <debugfs>/dynamic_debug/control
64 # filename:lineno [module]function flags format
65 /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"
66 /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:341 [svcxprt_rdma]svc_rdma_init =_ "\011max_inline : %d\012"
67 /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:340 [svcxprt_rdma]svc_rdma_init =_ "\011sq_depth : %d\012"
68 /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:338 [svcxprt_rdma]svc_rdma_init =_ "\011max_requests : %d\012"
69 ...
70
71
72You can also apply standard Unix text manipulation filters to this
73data, e.g.::
74
75 nullarbor:~ # grep -i rdma <debugfs>/dynamic_debug/control | wc -l
76 62
77
78 nullarbor:~ # grep -i tcp <debugfs>/dynamic_debug/control | wc -l
79 42
80
81The third column shows the currently enabled flags for each debug
82statement callsite (see below for definitions of the flags). The
83default value, with no flags enabled, is ``=_``. So you can view all
84the debug statement callsites with any non-default flags::
85
86 nullarbor:~ # awk '$3 != "=_"' <debugfs>/dynamic_debug/control
87 # filename:lineno [module]function flags format
88 /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"
89
90Command Language Reference
91==========================
92
93At the lexical level, a command comprises a sequence of words separated
94by spaces or tabs. So these are all equivalent::
95
96 nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' >
97 <debugfs>/dynamic_debug/control
98 nullarbor:~ # echo -n ' file svcsock.c line 1603 +p ' >
99 <debugfs>/dynamic_debug/control
100 nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' >
101 <debugfs>/dynamic_debug/control
102
103Command submissions are bounded by a write() system call.
104Multiple commands can be written together, separated by ``;`` or ``\n``::
105
106 ~# echo "func pnpacpi_get_resources +p; func pnp_assign_mem +p" \
107 > <debugfs>/dynamic_debug/control
108
109If your query set is big, you can batch them too::
110
111 ~# cat query-batch-file > <debugfs>/dynamic_debug/control
112
113A another way is to use wildcard. The match rule support ``*`` (matches
114zero or more characters) and ``?`` (matches exactly one character).For
115example, you can match all usb drivers::
116
117 ~# echo "file drivers/usb/* +p" > <debugfs>/dynamic_debug/control
118
119At the syntactical level, a command comprises a sequence of match
120specifications, followed by a flags change specification::
121
122 command ::= match-spec* flags-spec
123
124The match-spec's are used to choose a subset of the known pr_debug()
125callsites to which to apply the flags-spec. Think of them as a query
126with implicit ANDs between each pair. Note that an empty list of
127match-specs will select all debug statement callsites.
128
129A match specification comprises a keyword, which controls the
130attribute of the callsite to be compared, and a value to compare
131against. Possible keywords are:::
132
133 match-spec ::= 'func' string |
134 'file' string |
135 'module' string |
136 'format' string |
137 'line' line-range
138
139 line-range ::= lineno |
140 '-'lineno |
141 lineno'-' |
142 lineno'-'lineno
143
144 lineno ::= unsigned-int
145
146.. note::
147
148 ``line-range`` cannot contain space, e.g.
149 "1-30" is valid range but "1 - 30" is not.
150
151
152The meanings of each keyword are:
153
154func
155 The given string is compared against the function name
156 of each callsite. Example::
157
158 func svc_tcp_accept
159
160file
161 The given string is compared against either the full pathname, the
162 src-root relative pathname, or the basename of the source file of
163 each callsite. Examples::
164
165 file svcsock.c
166 file kernel/freezer.c
167 file /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svcsock.c
168
169module
170 The given string is compared against the module name
171 of each callsite. The module name is the string as
172 seen in ``lsmod``, i.e. without the directory or the ``.ko``
173 suffix and with ``-`` changed to ``_``. Examples::
174
175 module sunrpc
176 module nfsd
177
178format
179 The given string is searched for in the dynamic debug format
180 string. Note that the string does not need to match the
181 entire format, only some part. Whitespace and other
182 special characters can be escaped using C octal character
183 escape ``\ooo`` notation, e.g. the space character is ``\040``.
184 Alternatively, the string can be enclosed in double quote
185 characters (``"``) or single quote characters (``'``).
186 Examples::
187
188 format svcrdma: // many of the NFS/RDMA server pr_debugs
189 format readahead // some pr_debugs in the readahead cache
190 format nfsd:\040SETATTR // one way to match a format with whitespace
191 format "nfsd: SETATTR" // a neater way to match a format with whitespace
192 format 'nfsd: SETATTR' // yet another way to match a format with whitespace
193
194line
195 The given line number or range of line numbers is compared
196 against the line number of each ``pr_debug()`` callsite. A single
197 line number matches the callsite line number exactly. A
198 range of line numbers matches any callsite between the first
199 and last line number inclusive. An empty first number means
200 the first line in the file, an empty last line number means the
201 last line number in the file. Examples::
202
203 line 1603 // exactly line 1603
204 line 1600-1605 // the six lines from line 1600 to line 1605
205 line -1605 // the 1605 lines from line 1 to line 1605
206 line 1600- // all lines from line 1600 to the end of the file
207
208The flags specification comprises a change operation followed
209by one or more flag characters. The change operation is one
210of the characters::
211
212 - remove the given flags
213 + add the given flags
214 = set the flags to the given flags
215
216The flags are::
217
218 p enables the pr_debug() callsite.
219 f Include the function name in the printed message
220 l Include line number in the printed message
221 m Include module name in the printed message
222 t Include thread ID in messages not generated from interrupt context
223 _ No flags are set. (Or'd with others on input)
224
225For ``print_hex_dump_debug()`` and ``print_hex_dump_bytes()``, only ``p`` flag
226have meaning, other flags ignored.
227
228For display, the flags are preceded by ``=``
229(mnemonic: what the flags are currently equal to).
230
231Note the regexp ``^[-+=][flmpt_]+$`` matches a flags specification.
232To clear all flags at once, use ``=_`` or ``-flmpt``.
233
234
235Debug messages during Boot Process
236==================================
237
238To activate debug messages for core code and built-in modules during
239the boot process, even before userspace and debugfs exists, use
240``dyndbg="QUERY"``, ``module.dyndbg="QUERY"``, or ``ddebug_query="QUERY"``
241(``ddebug_query`` is obsoleted by ``dyndbg``, and deprecated). QUERY follows
242the syntax described above, but must not exceed 1023 characters. Your
243bootloader may impose lower limits.
244
245These ``dyndbg`` params are processed just after the ddebug tables are
246processed, as part of the arch_initcall. Thus you can enable debug
247messages in all code run after this arch_initcall via this boot
248parameter.
249
250On an x86 system for example ACPI enablement is a subsys_initcall and::
251
252 dyndbg="file ec.c +p"
253
254will show early Embedded Controller transactions during ACPI setup if
255your machine (typically a laptop) has an Embedded Controller.
256PCI (or other devices) initialization also is a hot candidate for using
257this boot parameter for debugging purposes.
258
259If ``foo`` module is not built-in, ``foo.dyndbg`` will still be processed at
260boot time, without effect, but will be reprocessed when module is
261loaded later. ``dyndbg_query=`` and bare ``dyndbg=`` are only processed at
262boot.
263
264
265Debug Messages at Module Initialization Time
266============================================
267
268When ``modprobe foo`` is called, modprobe scans ``/proc/cmdline`` for
269``foo.params``, strips ``foo.``, and passes them to the kernel along with
270params given in modprobe args or ``/etc/modprob.d/*.conf`` files,
271in the following order:
272
2731. parameters given via ``/etc/modprobe.d/*.conf``::
274
275 options foo dyndbg=+pt
276 options foo dyndbg # defaults to +p
277
2782. ``foo.dyndbg`` as given in boot args, ``foo.`` is stripped and passed::
279
280 foo.dyndbg=" func bar +p; func buz +mp"
281
2823. args to modprobe::
283
284 modprobe foo dyndbg==pmf # override previous settings
285
286These ``dyndbg`` queries are applied in order, with last having final say.
287This allows boot args to override or modify those from ``/etc/modprobe.d``
288(sensible, since 1 is system wide, 2 is kernel or boot specific), and
289modprobe args to override both.
290
291In the ``foo.dyndbg="QUERY"`` form, the query must exclude ``module foo``.
292``foo`` is extracted from the param-name, and applied to each query in
293``QUERY``, and only 1 match-spec of each type is allowed.
294
295The ``dyndbg`` option is a "fake" module parameter, which means:
296
297- modules do not need to define it explicitly
298- every module gets it tacitly, whether they use pr_debug or not
299- it doesn't appear in ``/sys/module/$module/parameters/``
300 To see it, grep the control file, or inspect ``/proc/cmdline.``
301
302For ``CONFIG_DYNAMIC_DEBUG`` kernels, any settings given at boot-time (or
303enabled by ``-DDEBUG`` flag during compilation) can be disabled later via
304the sysfs interface if the debug messages are no longer needed::
305
306 echo "module module_name -p" > <debugfs>/dynamic_debug/control
307
308Examples
309========
310
311::
312
313 // enable the message at line 1603 of file svcsock.c
314 nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' >
315 <debugfs>/dynamic_debug/control
316
317 // enable all the messages in file svcsock.c
318 nullarbor:~ # echo -n 'file svcsock.c +p' >
319 <debugfs>/dynamic_debug/control
320
321 // enable all the messages in the NFS server module
322 nullarbor:~ # echo -n 'module nfsd +p' >
323 <debugfs>/dynamic_debug/control
324
325 // enable all 12 messages in the function svc_process()
326 nullarbor:~ # echo -n 'func svc_process +p' >
327 <debugfs>/dynamic_debug/control
328
329 // disable all 12 messages in the function svc_process()
330 nullarbor:~ # echo -n 'func svc_process -p' >
331 <debugfs>/dynamic_debug/control
332
333 // enable messages for NFS calls READ, READLINK, READDIR and READDIR+.
334 nullarbor:~ # echo -n 'format "nfsd: READ" +p' >
335 <debugfs>/dynamic_debug/control
336
337 // enable messages in files of which the paths include string "usb"
338 nullarbor:~ # echo -n '*usb* +p' > <debugfs>/dynamic_debug/control
339
340 // enable all messages
341 nullarbor:~ # echo -n '+p' > <debugfs>/dynamic_debug/control
342
343 // add module, function to all enabled messages
344 nullarbor:~ # echo -n '+mf' > <debugfs>/dynamic_debug/control
345
346 // boot-args example, with newlines and comments for readability
347 Kernel command line: ...
348 // see whats going on in dyndbg=value processing
349 dynamic_debug.verbose=1
350 // enable pr_debugs in 2 builtins, #cmt is stripped
351 dyndbg="module params +p #cmt ; module sys +p"
352 // enable pr_debugs in 2 functions in a module loaded later
353 pc87360.dyndbg="func pc87360_init_device +p; func pc87360_find +p"