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Jason Baron86151fd2009-02-05 11:53:15 -05001
2Introduction
3============
4
Jim Cromie29e36c92012-04-27 14:30:41 -06005This document describes how to use the dynamic debug (dyndbg) feature.
Jason Baron86151fd2009-02-05 11:53:15 -05006
Jim Cromie29e36c92012-04-27 14:30:41 -06007Dynamic debug is designed to allow you to dynamically enable/disable
8kernel code to obtain additional kernel information. Currently, if
Vladimir Kondratiev7a555612012-12-05 16:48:27 -05009CONFIG_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.
Jason Baron86151fd2009-02-05 11:53:15 -050019
20Dynamic debug has even more useful features:
21
Jim Cromie29e36c92012-04-27 14:30:41 -060022 * Simple query language allows turning on and off debugging
23 statements by matching any combination of 0 or 1 of:
Jason Baron86151fd2009-02-05 11:53:15 -050024
25 - source filename
26 - function name
27 - line number (including ranges of line numbers)
28 - module name
29 - format string
30
Jim Cromie29e36c92012-04-27 14:30:41 -060031 * 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
Jason Baron86151fd2009-02-05 11:53:15 -050034
35Controlling dynamic debug Behaviour
Thomas Renningera648ec02010-08-06 16:11:02 +020036===================================
Jason Baron86151fd2009-02-05 11:53:15 -050037
Jonathan Corbet9cad7962011-03-25 10:42:17 -060038The behaviour of pr_debug()/dev_dbg()s are controlled via writing to a
Jim Cromie29e36c92012-04-27 14:30:41 -060039control 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:
Jason Baron86151fd2009-02-05 11:53:15 -050044
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
Jim Cromie29e36c92012-04-27 14:30:41 -060057You can view the currently configured behaviour of all the debug
58statements via:
Jason Baron86151fd2009-02-05 11:53:15 -050059
60nullarbor:~ # cat <debugfs>/dynamic_debug/control
61# filename:lineno [module]function flags format
Jim Cromie29e36c92012-04-27 14:30:41 -060062/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"
Jason Baron86151fd2009-02-05 11:53:15 -050066...
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
Jim Cromie29e36c92012-04-27 14:30:41 -060078The 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:
Jason Baron86151fd2009-02-05 11:53:15 -050082
Jim Cromie29e36c92012-04-27 14:30:41 -060083nullarbor:~ # awk '$3 != "=_"' <debugfs>/dynamic_debug/control
Jason Baron86151fd2009-02-05 11:53:15 -050084# filename:lineno [module]function flags format
Greg Banks9898abb2009-02-06 12:54:26 +110085/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"
Jason Baron86151fd2009-02-05 11:53:15 -050086
87
88Command Language Reference
89==========================
90
91At the lexical level, a command comprises a sequence of words separated
Jim Cromie85f7f6c2011-12-19 17:13:21 -050092by spaces or tabs. So these are all equivalent:
Jason Baron86151fd2009-02-05 11:53:15 -050093
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
Jason Baron86151fd2009-02-05 11:53:15 -050098nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' >
99 <debugfs>/dynamic_debug/control
100
Jim Cromie85f7f6c2011-12-19 17:13:21 -0500101Command submissions are bounded by a write() system call.
102Multiple commands can be written together, separated by ';' or '\n'.
Jason Baron86151fd2009-02-05 11:53:15 -0500103
Jim Cromie85f7f6c2011-12-19 17:13:21 -0500104 ~# echo "func pnpacpi_get_resources +p; func pnp_assign_mem +p" \
105 > <debugfs>/dynamic_debug/control
Jason Baron86151fd2009-02-05 11:53:15 -0500106
Jim Cromie85f7f6c2011-12-19 17:13:21 -0500107If your query set is big, you can batch them too:
Jason Baron86151fd2009-02-05 11:53:15 -0500108
Jim Cromie85f7f6c2011-12-19 17:13:21 -0500109 ~# cat query-batch-file > <debugfs>/dynamic_debug/control
Jason Baron86151fd2009-02-05 11:53:15 -0500110
Du, Changbin8f073bd2014-01-23 15:54:15 -0800111A 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
Jason Baron86151fd2009-02-05 11:53:15 -0500117At the syntactical level, a command comprises a sequence of match
118specifications, followed by a flags change specification.
119
120command ::= match-spec* flags-spec
121
Jim Cromie29e36c92012-04-27 14:30:41 -0600122The match-spec's are used to choose a subset of the known pr_debug()
Jason Baron86151fd2009-02-05 11:53:15 -0500123callsites 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
Jim Cromie29e36c92012-04-27 14:30:41 -0600125match-specs will select all debug statement callsites.
Jason Baron86151fd2009-02-05 11:53:15 -0500126
Jim Cromie29e36c92012-04-27 14:30:41 -0600127A match specification comprises a keyword, which controls the
128attribute of the callsite to be compared, and a value to compare
129against. Possible keywords are:
Jason Baron86151fd2009-02-05 11:53:15 -0500130
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
Jim Cromie2b678312011-12-19 17:13:12 -0500155 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:
Jason Baron86151fd2009-02-05 11:53:15 -0500158
159 file svcsock.c
Jim Cromie2b678312011-12-19 17:13:12 -0500160 file kernel/freezer.c
Jason Baron86151fd2009-02-05 11:53:15 -0500161 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.
Greg Banks9898abb2009-02-06 12:54:26 +1100178 Alternatively, the string can be enclosed in double quote
179 characters (") or single quote characters (').
Jason Baron86151fd2009-02-05 11:53:15 -0500180 Examples:
181
Jim Cromie29e36c92012-04-27 14:30:41 -0600182 format svcrdma: // many of the NFS/RDMA server pr_debugs
183 format readahead // some pr_debugs in the readahead cache
Greg Banks9898abb2009-02-06 12:54:26 +1100184 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
Jason Baron86151fd2009-02-05 11:53:15 -0500187
188line
189 The given line number or range of line numbers is compared
Jim Cromie29e36c92012-04-27 14:30:41 -0600190 against the line number of each pr_debug() callsite. A single
Jason Baron86151fd2009-02-05 11:53:15 -0500191 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
Jim Cromie29e36c92012-04-27 14:30:41 -0600206 - remove the given flags
207 + add the given flags
208 = set the flags to the given flags
Jason Baron86151fd2009-02-05 11:53:15 -0500209
210The flags are:
211
Jim Cromie29e36c92012-04-27 14:30:41 -0600212 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)
Jason Baron86151fd2009-02-05 11:53:15 -0500218
Vladimir Kondratiev7a555612012-12-05 16:48:27 -0500219For print_hex_dump_debug() and print_hex_dump_bytes(), only 'p' flag
220have meaning, other flags ignored.
221
Jim Cromie29e36c92012-04-27 14:30:41 -0600222For 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".
Jason Baron86151fd2009-02-05 11:53:15 -0500227
Thomas Renningera648ec02010-08-06 16:11:02 +0200228
Jim Cromie29e36c92012-04-27 14:30:41 -0600229Debug messages during Boot Process
Thomas Renningera648ec02010-08-06 16:11:02 +0200230==================================
231
Jim Cromie29e36c92012-04-27 14:30:41 -0600232To 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.
Thomas Renningera648ec02010-08-06 16:11:02 +0200238
Jim Cromie29e36c92012-04-27 14:30:41 -0600239These 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
Thomas Renningera648ec02010-08-06 16:11:02 +0200244On an x86 system for example ACPI enablement is a subsys_initcall and
Jim Cromie29e36c92012-04-27 14:30:41 -0600245 dyndbg="file ec.c +p"
Thomas Renningera648ec02010-08-06 16:11:02 +0200246will 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
Jim Cromie29e36c92012-04-27 14:30:41 -0600251If 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
Anatol Pomozovf884ab12013-05-08 16:56:16 -0700288- it doesn't appear in /sys/module/$module/parameters/
Jim Cromie29e36c92012-04-27 14:30:41 -0600289 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
Thomas Renningera648ec02010-08-06 16:11:02 +0200296
Jason Baron86151fd2009-02-05 11:53:15 -0500297Examples
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
Greg Banks9898abb2009-02-06 12:54:26 +1100319
320// enable messages for NFS calls READ, READLINK, READDIR and READDIR+.
321nullarbor:~ # echo -n 'format "nfsd: READ" +p' >
322 <debugfs>/dynamic_debug/control
Jim Cromie29e36c92012-04-27 14:30:41 -0600323
Du, Changbin8f073bd2014-01-23 15:54:15 -0800324// enable messages in files of which the pathes include string "usb"
325nullarbor:~ # echo -n '*usb* +p' > <debugfs>/dynamic_debug/control
326
Jim Cromie29e36c92012-04-27 14:30:41 -0600327// 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"