dynamic_debug

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 transport12"
63/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:341 [svcxprt_rdma]svc_rdma_init =_ "11max_inline       : %d12"
64/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:340 [svcxprt_rdma]svc_rdma_init =_ "11sq_depth         : %d12"
65/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:338 [svcxprt_rdma]svc_rdma_init =_ "11max_requests     : %d12"
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 %d12"
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
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
116The match-spec's are used to choose a subset of the known pr_debug()
117callsites 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
119match-specs will select all debug statement callsites.
120
121A match specification comprises a keyword, which controls the
122attribute of the callsite to be compared, and a value to compare
123against.  Possible keywords are:
124
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
149    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:
152
153    file svcsock.c
154    file kernel/freezer.c
155    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 40.
172    Alternatively, the string can be enclosed in double quote
173    characters (") or single quote characters (').
174    Examples:
175
176    format svcrdma:	    // many of the NFS/RDMA server pr_debugs
177    format readahead	    // some pr_debugs in the readahead cache
178    format nfsd:40SETATTR // 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
181
182line
183    The given line number or range of line numbers is compared
184    against the line number of each pr_debug() callsite.  A single
185    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
200  -    remove the given flags
201  +    add the given flags
202  =    set the flags to the given flags
203
204The flags are:
205
206  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)
212
213For print_hex_dump_debug() and print_hex_dump_bytes(), only 'p' flag
214have meaning, other flags ignored.
215
216For 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".
221
222
223Debug messages during Boot Process
224==================================
225
226To 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.
232
233These 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
238On an x86 system for example ACPI enablement is a subsys_initcall and
239   dyndbg="file ec.c +p"
240will 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
245If 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
290
291Examples
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
313
314// enable messages for NFS calls READ, READLINK, READDIR and READDIR+.
315nullarbor:~ # echo -n 'format "nfsd: READ" +p' >
316				<debugfs>/dynamic_debug/control
317
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"

332(http:..../android/xref/Q8-A6/android/kernel/Documentation/dynamic-debug-howto.txt#9)