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1Dynamic debug
2+++++++++++++
3
4
5Introduction
6============
7
8Dynamic debug allows you to dynamically enable/disable kernel
9debug-print code to obtain additional kernel information.
10
11If ``/proc/dynamic_debug/control`` exists, your kernel has dynamic
12debug. You'll need root access (sudo su) to use this.
13
14Dynamic debug provides:
15
16 * a Catalog of all *prdbgs* in your kernel.
17 ``cat /proc/dynamic_debug/control`` to see them.
18
19 * a Simple query/command language to alter *prdbgs* by selecting on
20 any combination of 0 or 1 of:
21
22 - source filename
23 - function name
24 - line number (including ranges of line numbers)
25 - module name
26 - format string
27 - class name (as known/declared by each module)
28
29NOTE: To actually get the debug-print output on the console, you may
30need to adjust the kernel ``loglevel=``, or use ``ignore_loglevel``.
31Read about these kernel parameters in
32Documentation/admin-guide/kernel-parameters.rst.
33
34Viewing Dynamic Debug Behaviour
35===============================
36
37You can view the currently configured behaviour in the *prdbg* catalog::
38
39 :#> head -n7 /proc/dynamic_debug/control
40 # filename:lineno [module]function flags format
41 init/main.c:1179 [main]initcall_blacklist =_ "blacklisting initcall %s\012
42 init/main.c:1218 [main]initcall_blacklisted =_ "initcall %s blacklisted\012"
43 init/main.c:1424 [main]run_init_process =_ " with arguments:\012"
44 init/main.c:1426 [main]run_init_process =_ " %s\012"
45 init/main.c:1427 [main]run_init_process =_ " with environment:\012"
46 init/main.c:1429 [main]run_init_process =_ " %s\012"
47
48The 3rd space-delimited column shows the current flags, preceded by
49a ``=`` for easy use with grep/cut. ``=p`` shows enabled callsites.
50
51Controlling dynamic debug Behaviour
52===================================
53
54The behaviour of *prdbg* sites are controlled by writing
55query/commands to the control file. Example::
56
57 # grease the interface
58 :#> alias ddcmd='echo $* > /proc/dynamic_debug/control'
59
60 :#> ddcmd '-p; module main func run* +p'
61 :#> grep =p /proc/dynamic_debug/control
62 init/main.c:1424 [main]run_init_process =p " with arguments:\012"
63 init/main.c:1426 [main]run_init_process =p " %s\012"
64 init/main.c:1427 [main]run_init_process =p " with environment:\012"
65 init/main.c:1429 [main]run_init_process =p " %s\012"
66
67Error messages go to console/syslog::
68
69 :#> ddcmd mode foo +p
70 dyndbg: unknown keyword "mode"
71 dyndbg: query parse failed
72 bash: echo: write error: Invalid argument
73
74If debugfs is also enabled and mounted, ``dynamic_debug/control`` is
75also under the mount-dir, typically ``/sys/kernel/debug/``.
76
77Command Language Reference
78==========================
79
80At the basic lexical level, a command is a sequence of words separated
81by spaces or tabs. So these are all equivalent::
82
83 :#> ddcmd file svcsock.c line 1603 +p
84 :#> ddcmd "file svcsock.c line 1603 +p"
85 :#> ddcmd ' file svcsock.c line 1603 +p '
86
87Command submissions are bounded by a write() system call.
88Multiple commands can be written together, separated by ``;`` or ``\n``::
89
90 :#> ddcmd "func pnpacpi_get_resources +p; func pnp_assign_mem +p"
91 :#> ddcmd <<"EOC"
92 func pnpacpi_get_resources +p
93 func pnp_assign_mem +p
94 EOC
95 :#> cat query-batch-file > /proc/dynamic_debug/control
96
97You can also use wildcards in each query term. The match rule supports
98``*`` (matches zero or more characters) and ``?`` (matches exactly one
99character). For example, you can match all usb drivers::
100
101 :#> ddcmd file "drivers/usb/*" +p # "" to suppress shell expansion
102
103Syntactically, a command is pairs of keyword values, followed by a
104flags change or setting::
105
106 command ::= match-spec* flags-spec
107
108The match-spec's select *prdbgs* from the catalog, upon which to apply
109the flags-spec, all constraints are ANDed together. An absent keyword
110is the same as keyword "*".
111
112
113A match specification is a keyword, which selects the attribute of
114the callsite to be compared, and a value to compare against. Possible
115keywords are:::
116
117 match-spec ::= 'func' string |
118 'file' string |
119 'module' string |
120 'format' string |
121 'class' string |
122 'line' line-range
123
124 line-range ::= lineno |
125 '-'lineno |
126 lineno'-' |
127 lineno'-'lineno
128
129 lineno ::= unsigned-int
130
131.. note::
132
133 ``line-range`` cannot contain space, e.g.
134 "1-30" is valid range but "1 - 30" is not.
135
136
137The meanings of each keyword are:
138
139func
140 The given string is compared against the function name
141 of each callsite. Example::
142
143 func svc_tcp_accept
144 func *recv* # in rfcomm, bluetooth, ping, tcp
145
146file
147 The given string is compared against either the src-root relative
148 pathname, or the basename of the source file of each callsite.
149 Examples::
150
151 file svcsock.c
152 file kernel/freezer.c # ie column 1 of control file
153 file drivers/usb/* # all callsites under it
154 file inode.c:start_* # parse :tail as a func (above)
155 file inode.c:1-100 # parse :tail as a line-range (above)
156
157module
158 The given string is compared against the module name
159 of each callsite. The module name is the string as
160 seen in ``lsmod``, i.e. without the directory or the ``.ko``
161 suffix and with ``-`` changed to ``_``. Examples::
162
163 module sunrpc
164 module nfsd
165 module drm* # both drm, drm_kms_helper
166
167format
168 The given string is searched for in the dynamic debug format
169 string. Note that the string does not need to match the
170 entire format, only some part. Whitespace and other
171 special characters can be escaped using C octal character
172 escape ``\ooo`` notation, e.g. the space character is ``\040``.
173 Alternatively, the string can be enclosed in double quote
174 characters (``"``) or single quote characters (``'``).
175 Examples::
176
177 format svcrdma: // many of the NFS/RDMA server pr_debugs
178 format readahead // some pr_debugs in the readahead cache
179 format nfsd:\040SETATTR // one way to match a format with whitespace
180 format "nfsd: SETATTR" // a neater way to match a format with whitespace
181 format 'nfsd: SETATTR' // yet another way to match a format with whitespace
182
183class
184 The given class_name is validated against each module, which may
185 have declared a list of known class_names. If the class_name is
186 found for a module, callsite & class matching and adjustment
187 proceeds. Examples::
188
189 class DRM_UT_KMS # a DRM.debug category
190 class JUNK # silent non-match
191 // class TLD_* # NOTICE: no wildcard in class names
192
193line
194 The given line number or range of line numbers is compared
195 against the line number of each ``pr_debug()`` callsite. A single
196 line number matches the callsite line number exactly. A
197 range of line numbers matches any callsite between the first
198 and last line number inclusive. An empty first number means
199 the first line in the file, an empty last line number means the
200 last line number in the file. Examples::
201
202 line 1603 // exactly line 1603
203 line 1600-1605 // the six lines from line 1600 to line 1605
204 line -1605 // the 1605 lines from line 1 to line 1605
205 line 1600- // all lines from line 1600 to the end of the file
206
207The flags specification comprises a change operation followed
208by one or more flag characters. The change operation is one
209of the characters::
210
211 - remove the given flags
212 + add the given flags
213 = set the flags to the given flags
214
215The flags are::
216
217 p enables the pr_debug() callsite.
218 _ enables no flags.
219
220 Decorator flags add to the message-prefix, in order:
221 t Include thread ID, or <intr>
222 m Include module name
223 f Include the function name
224 s Include the source file name
225 l Include line number
226
227For ``print_hex_dump_debug()`` and ``print_hex_dump_bytes()``, only
228the ``p`` flag has meaning, other flags are ignored.
229
230Note the regexp ``^[-+=][fslmpt_]+$`` matches a flags specification.
231To clear all flags at once, use ``=_`` or ``-fslmpt``.
232
233
234Debug messages during Boot Process
235==================================
236
237To activate debug messages for core code and built-in modules during
238the boot process, even before userspace and debugfs exists, use
239``dyndbg="QUERY"`` or ``module.dyndbg="QUERY"``. QUERY follows
240the syntax described above, but must not exceed 1023 characters. Your
241bootloader may impose lower limits.
242
243These ``dyndbg`` params are processed just after the ddebug tables are
244processed, as part of the early_initcall. Thus you can enable debug
245messages in all code run after this early_initcall via this boot
246parameter.
247
248On an x86 system for example ACPI enablement is a subsys_initcall and::
249
250 dyndbg="file ec.c +p"
251
252will show early Embedded Controller transactions during ACPI setup if
253your machine (typically a laptop) has an Embedded Controller.
254PCI (or other devices) initialization also is a hot candidate for using
255this boot parameter for debugging purposes.
256
257If ``foo`` module is not built-in, ``foo.dyndbg`` will still be processed at
258boot time, without effect, but will be reprocessed when module is
259loaded later. Bare ``dyndbg=`` is only processed at boot.
260
261
262Debug Messages at Module Initialization Time
263============================================
264
265When ``modprobe foo`` is called, modprobe scans ``/proc/cmdline`` for
266``foo.params``, strips ``foo.``, and passes them to the kernel along with
267params given in modprobe args or ``/etc/modprobe.d/*.conf`` files,
268in the following order:
269
2701. parameters given via ``/etc/modprobe.d/*.conf``::
271
272 options foo dyndbg=+pt
273 options foo dyndbg # defaults to +p
274
2752. ``foo.dyndbg`` as given in boot args, ``foo.`` is stripped and passed::
276
277 foo.dyndbg=" func bar +p; func buz +mp"
278
2793. args to modprobe::
280
281 modprobe foo dyndbg==pmf # override previous settings
282
283These ``dyndbg`` queries are applied in order, with last having final say.
284This allows boot args to override or modify those from ``/etc/modprobe.d``
285(sensible, since 1 is system wide, 2 is kernel or boot specific), and
286modprobe args to override both.
287
288In the ``foo.dyndbg="QUERY"`` form, the query must exclude ``module foo``.
289``foo`` is extracted from the param-name, and applied to each query in
290``QUERY``, and only 1 match-spec of each type is allowed.
291
292The ``dyndbg`` option is a "fake" module parameter, which means:
293
294- modules do not need to define it explicitly
295- every module gets it tacitly, whether they use pr_debug or not
296- it doesn't appear in ``/sys/module/$module/parameters/``
297 To see it, grep the control file, or inspect ``/proc/cmdline.``
298
299For ``CONFIG_DYNAMIC_DEBUG`` kernels, any settings given at boot-time (or
300enabled by ``-DDEBUG`` flag during compilation) can be disabled later via
301the debugfs interface if the debug messages are no longer needed::
302
303 echo "module module_name -p" > /proc/dynamic_debug/control
304
305Examples
306========
307
308::
309
310 // enable the message at line 1603 of file svcsock.c
311 :#> ddcmd 'file svcsock.c line 1603 +p'
312
313 // enable all the messages in file svcsock.c
314 :#> ddcmd 'file svcsock.c +p'
315
316 // enable all the messages in the NFS server module
317 :#> ddcmd 'module nfsd +p'
318
319 // enable all 12 messages in the function svc_process()
320 :#> ddcmd 'func svc_process +p'
321
322 // disable all 12 messages in the function svc_process()
323 :#> ddcmd 'func svc_process -p'
324
325 // enable messages for NFS calls READ, READLINK, READDIR and READDIR+.
326 :#> ddcmd 'format "nfsd: READ" +p'
327
328 // enable messages in files of which the paths include string "usb"
329 :#> ddcmd 'file *usb* +p'
330
331 // enable all messages
332 :#> ddcmd '+p'
333
334 // add module, function to all enabled messages
335 :#> ddcmd '+mf'
336
337 // boot-args example, with newlines and comments for readability
338 Kernel command line: ...
339 // see what's going on in dyndbg=value processing
340 dynamic_debug.verbose=3
341 // enable pr_debugs in the btrfs module (can be builtin or loadable)
342 btrfs.dyndbg="+p"
343 // enable pr_debugs in all files under init/
344 // and the function parse_one, #cmt is stripped
345 dyndbg="file init/* +p #cmt ; func parse_one +p"
346 // enable pr_debugs in 2 functions in a module loaded later
347 pc87360.dyndbg="func pc87360_init_device +p; func pc87360_find +p"
348
349Kernel Configuration
350====================
351
352Dynamic Debug is enabled via kernel config items::
353
354 CONFIG_DYNAMIC_DEBUG=y # build catalog, enables CORE
355 CONFIG_DYNAMIC_DEBUG_CORE=y # enable mechanics only, skip catalog
356
357If you do not want to enable dynamic debug globally (i.e. in some embedded
358system), you may set ``CONFIG_DYNAMIC_DEBUG_CORE`` as basic support of dynamic
359debug and add ``ccflags := -DDYNAMIC_DEBUG_MODULE`` into the Makefile of any
360modules which you'd like to dynamically debug later.
361
362
363Kernel *prdbg* API
364==================
365
366The following functions are cataloged and controllable when dynamic
367debug is enabled::
368
369 pr_debug()
370 dev_dbg()
371 print_hex_dump_debug()
372 print_hex_dump_bytes()
373
374Otherwise, they are off by default; ``ccflags += -DDEBUG`` or
375``#define DEBUG`` in a source file will enable them appropriately.
376
377If ``CONFIG_DYNAMIC_DEBUG`` is not set, ``print_hex_dump_debug()`` is
378just a shortcut for ``print_hex_dump(KERN_DEBUG)``.
379
380For ``print_hex_dump_debug()``/``print_hex_dump_bytes()``, format string is
381its ``prefix_str`` argument, if it is constant string; or ``hexdump``
382in case ``prefix_str`` is built dynamically.
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 build 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 -c 'file svcsock.c line 1603 +p' >
97 <debugfs>/dynamic_debug/control
98 nullarbor:~ # echo -c ' 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 line number means the
201 last 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"