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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 paths 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"
341