blob: 72322c6d7352a908bb5ed1d1c0fc86735f198b4f [file] [log] [blame]
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
111At the syntactical level, a command comprises a sequence of match
112specifications, followed by a flags change specification.
113
114command ::= match-spec* flags-spec
115
Jim Cromie29e36c92012-04-27 14:30:41 -0600116The match-spec's are used to choose a subset of the known pr_debug()
Jason Baron86151fd2009-02-05 11:53:15 -0500117callsites to which to apply the flags-spec. Think of them as a query
118with implicit ANDs between each pair. Note that an empty list of
Jim Cromie29e36c92012-04-27 14:30:41 -0600119match-specs will select all debug statement callsites.
Jason Baron86151fd2009-02-05 11:53:15 -0500120
Jim Cromie29e36c92012-04-27 14:30:41 -0600121A match specification comprises a keyword, which controls the
122attribute of the callsite to be compared, and a value to compare
123against. Possible keywords are:
Jason Baron86151fd2009-02-05 11:53:15 -0500124
125match-spec ::= 'func' string |
126 'file' string |
127 'module' string |
128 'format' string |
129 'line' line-range
130
131line-range ::= lineno |
132 '-'lineno |
133 lineno'-' |
134 lineno'-'lineno
135// Note: line-range cannot contain space, e.g.
136// "1-30" is valid range but "1 - 30" is not.
137
138lineno ::= unsigned-int
139
140The meanings of each keyword are:
141
142func
143 The given string is compared against the function name
144 of each callsite. Example:
145
146 func svc_tcp_accept
147
148file
Jim Cromie2b678312011-12-19 17:13:12 -0500149 The given string is compared against either the full pathname, the
150 src-root relative pathname, or the basename of the source file of
151 each callsite. Examples:
Jason Baron86151fd2009-02-05 11:53:15 -0500152
153 file svcsock.c
Jim Cromie2b678312011-12-19 17:13:12 -0500154 file kernel/freezer.c
Jason Baron86151fd2009-02-05 11:53:15 -0500155 file /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svcsock.c
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
166format
167 The given string is searched for in the dynamic debug format
168 string. Note that the string does not need to match the
169 entire format, only some part. Whitespace and other
170 special characters can be escaped using C octal character
171 escape \ooo notation, e.g. the space character is \040.
Greg Banks9898abb2009-02-06 12:54:26 +1100172 Alternatively, the string can be enclosed in double quote
173 characters (") or single quote characters (').
Jason Baron86151fd2009-02-05 11:53:15 -0500174 Examples:
175
Jim Cromie29e36c92012-04-27 14:30:41 -0600176 format svcrdma: // many of the NFS/RDMA server pr_debugs
177 format readahead // some pr_debugs in the readahead cache
Greg Banks9898abb2009-02-06 12:54:26 +1100178 format nfsd:\040SETATTR // one way to match a format with whitespace
179 format "nfsd: SETATTR" // a neater way to match a format with whitespace
180 format 'nfsd: SETATTR' // yet another way to match a format with whitespace
Jason Baron86151fd2009-02-05 11:53:15 -0500181
182line
183 The given line number or range of line numbers is compared
Jim Cromie29e36c92012-04-27 14:30:41 -0600184 against the line number of each pr_debug() callsite. A single
Jason Baron86151fd2009-02-05 11:53:15 -0500185 line number matches the callsite line number exactly. A
186 range of line numbers matches any callsite between the first
187 and last line number inclusive. An empty first number means
188 the first line in the file, an empty line number means the
189 last number in the file. Examples:
190
191 line 1603 // exactly line 1603
192 line 1600-1605 // the six lines from line 1600 to line 1605
193 line -1605 // the 1605 lines from line 1 to line 1605
194 line 1600- // all lines from line 1600 to the end of the file
195
196The flags specification comprises a change operation followed
197by one or more flag characters. The change operation is one
198of the characters:
199
Jim Cromie29e36c92012-04-27 14:30:41 -0600200 - remove the given flags
201 + add the given flags
202 = set the flags to the given flags
Jason Baron86151fd2009-02-05 11:53:15 -0500203
204The flags are:
205
Jim Cromie29e36c92012-04-27 14:30:41 -0600206 p enables the pr_debug() callsite.
207 f Include the function name in the printed message
208 l Include line number in the printed message
209 m Include module name in the printed message
210 t Include thread ID in messages not generated from interrupt context
211 _ No flags are set. (Or'd with others on input)
Jason Baron86151fd2009-02-05 11:53:15 -0500212
Vladimir Kondratiev7a555612012-12-05 16:48:27 -0500213For print_hex_dump_debug() and print_hex_dump_bytes(), only 'p' flag
214have meaning, other flags ignored.
215
Jim Cromie29e36c92012-04-27 14:30:41 -0600216For display, the flags are preceded by '='
217(mnemonic: what the flags are currently equal to).
218
219Note the regexp ^[-+=][flmpt_]+$ matches a flags specification.
220To clear all flags at once, use "=_" or "-flmpt".
Jason Baron86151fd2009-02-05 11:53:15 -0500221
Thomas Renningera648ec02010-08-06 16:11:02 +0200222
Jim Cromie29e36c92012-04-27 14:30:41 -0600223Debug messages during Boot Process
Thomas Renningera648ec02010-08-06 16:11:02 +0200224==================================
225
Jim Cromie29e36c92012-04-27 14:30:41 -0600226To activate debug messages for core code and built-in modules during
227the boot process, even before userspace and debugfs exists, use
228dyndbg="QUERY", module.dyndbg="QUERY", or ddebug_query="QUERY"
229(ddebug_query is obsoleted by dyndbg, and deprecated). QUERY follows
230the syntax described above, but must not exceed 1023 characters. Your
231bootloader may impose lower limits.
Thomas Renningera648ec02010-08-06 16:11:02 +0200232
Jim Cromie29e36c92012-04-27 14:30:41 -0600233These dyndbg params are processed just after the ddebug tables are
234processed, as part of the arch_initcall. Thus you can enable debug
235messages in all code run after this arch_initcall via this boot
236parameter.
237
Thomas Renningera648ec02010-08-06 16:11:02 +0200238On an x86 system for example ACPI enablement is a subsys_initcall and
Jim Cromie29e36c92012-04-27 14:30:41 -0600239 dyndbg="file ec.c +p"
Thomas Renningera648ec02010-08-06 16:11:02 +0200240will show early Embedded Controller transactions during ACPI setup if
241your machine (typically a laptop) has an Embedded Controller.
242PCI (or other devices) initialization also is a hot candidate for using
243this boot parameter for debugging purposes.
244
Jim Cromie29e36c92012-04-27 14:30:41 -0600245If foo module is not built-in, foo.dyndbg will still be processed at
246boot time, without effect, but will be reprocessed when module is
247loaded later. dyndbg_query= and bare dyndbg= are only processed at
248boot.
249
250
251Debug Messages at Module Initialization Time
252============================================
253
254When "modprobe foo" is called, modprobe scans /proc/cmdline for
255foo.params, strips "foo.", and passes them to the kernel along with
256params given in modprobe args or /etc/modprob.d/*.conf files,
257in the following order:
258
2591. # parameters given via /etc/modprobe.d/*.conf
260 options foo dyndbg=+pt
261 options foo dyndbg # defaults to +p
262
2632. # foo.dyndbg as given in boot args, "foo." is stripped and passed
264 foo.dyndbg=" func bar +p; func buz +mp"
265
2663. # args to modprobe
267 modprobe foo dyndbg==pmf # override previous settings
268
269These dyndbg queries are applied in order, with last having final say.
270This allows boot args to override or modify those from /etc/modprobe.d
271(sensible, since 1 is system wide, 2 is kernel or boot specific), and
272modprobe args to override both.
273
274In the foo.dyndbg="QUERY" form, the query must exclude "module foo".
275"foo" is extracted from the param-name, and applied to each query in
276"QUERY", and only 1 match-spec of each type is allowed.
277
278The dyndbg option is a "fake" module parameter, which means:
279
280- modules do not need to define it explicitly
281- every module gets it tacitly, whether they use pr_debug or not
282- it doesnt appear in /sys/module/$module/parameters/
283 To see it, grep the control file, or inspect /proc/cmdline.
284
285For CONFIG_DYNAMIC_DEBUG kernels, any settings given at boot-time (or
286enabled by -DDEBUG flag during compilation) can be disabled later via
287the sysfs interface if the debug messages are no longer needed:
288
289 echo "module module_name -p" > <debugfs>/dynamic_debug/control
Thomas Renningera648ec02010-08-06 16:11:02 +0200290
Jason Baron86151fd2009-02-05 11:53:15 -0500291Examples
292========
293
294// enable the message at line 1603 of file svcsock.c
295nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' >
296 <debugfs>/dynamic_debug/control
297
298// enable all the messages in file svcsock.c
299nullarbor:~ # echo -n 'file svcsock.c +p' >
300 <debugfs>/dynamic_debug/control
301
302// enable all the messages in the NFS server module
303nullarbor:~ # echo -n 'module nfsd +p' >
304 <debugfs>/dynamic_debug/control
305
306// enable all 12 messages in the function svc_process()
307nullarbor:~ # echo -n 'func svc_process +p' >
308 <debugfs>/dynamic_debug/control
309
310// disable all 12 messages in the function svc_process()
311nullarbor:~ # echo -n 'func svc_process -p' >
312 <debugfs>/dynamic_debug/control
Greg Banks9898abb2009-02-06 12:54:26 +1100313
314// enable messages for NFS calls READ, READLINK, READDIR and READDIR+.
315nullarbor:~ # echo -n 'format "nfsd: READ" +p' >
316 <debugfs>/dynamic_debug/control
Jim Cromie29e36c92012-04-27 14:30:41 -0600317
318// enable all messages
319nullarbor:~ # echo -n '+p' > <debugfs>/dynamic_debug/control
320
321// add module, function to all enabled messages
322nullarbor:~ # echo -n '+mf' > <debugfs>/dynamic_debug/control
323
324// boot-args example, with newlines and comments for readability
325Kernel command line: ...
326 // see whats going on in dyndbg=value processing
327 dynamic_debug.verbose=1
328 // enable pr_debugs in 2 builtins, #cmt is stripped
329 dyndbg="module params +p #cmt ; module sys +p"
330 // enable pr_debugs in 2 functions in a module loaded later
331 pc87360.dyndbg="func pc87360_init_device +p; func pc87360_find +p"