8 Dynamic debug allows you to dynamically enable/disable kernel
9 debug-print code to obtain additional kernel information.
11 If ``/proc/dynamic_debug/control`` exists, your kernel has dynamic
12 debug. You'll need root access (sudo su) to use this.
14 Dynamic debug provides:
16 * a Catalog of all *prdbgs* in your kernel.
17 ``cat /proc/dynamic_debug/control`` to see them.
19 * a Simple query/command language to alter *prdbgs* by selecting on
20 any combination of 0 or 1 of:
24 - line number (including ranges of line numbers)
27 - class name (as known/declared by each module)
29 Viewing Dynamic Debug Behaviour
30 ===============================
32 You can view the currently configured behaviour in the *prdbg* catalog::
34 :#> head -n7 /proc/dynamic_debug/control
35 # filename:lineno [module]function flags format
36 init/main.c:1179 [main]initcall_blacklist =_ "blacklisting initcall %s\012
37 init/main.c:1218 [main]initcall_blacklisted =_ "initcall %s blacklisted\012"
38 init/main.c:1424 [main]run_init_process =_ " with arguments:\012"
39 init/main.c:1426 [main]run_init_process =_ " %s\012"
40 init/main.c:1427 [main]run_init_process =_ " with environment:\012"
41 init/main.c:1429 [main]run_init_process =_ " %s\012"
43 The 3rd space-delimited column shows the current flags, preceded by
44 a ``=`` for easy use with grep/cut. ``=p`` shows enabled callsites.
46 Controlling dynamic debug Behaviour
47 ===================================
49 The behaviour of *prdbg* sites are controlled by writing
50 query/commands to the control file. Example::
52 # grease the interface
53 :#> alias ddcmd='echo $* > /proc/dynamic_debug/control'
55 :#> ddcmd '-p; module main func run* +p'
56 :#> grep =p /proc/dynamic_debug/control
57 init/main.c:1424 [main]run_init_process =p " with arguments:\012"
58 init/main.c:1426 [main]run_init_process =p " %s\012"
59 init/main.c:1427 [main]run_init_process =p " with environment:\012"
60 init/main.c:1429 [main]run_init_process =p " %s\012"
62 Error messages go to console/syslog::
65 dyndbg: unknown keyword "mode"
66 dyndbg: query parse failed
67 bash: echo: write error: Invalid argument
69 If debugfs is also enabled and mounted, ``dynamic_debug/control`` is
70 also under the mount-dir, typically ``/sys/kernel/debug/``.
72 Command Language Reference
73 ==========================
75 At the basic lexical level, a command is a sequence of words separated
76 by spaces or tabs. So these are all equivalent::
78 :#> ddcmd file svcsock.c line 1603 +p
79 :#> ddcmd "file svcsock.c line 1603 +p"
80 :#> ddcmd ' file svcsock.c line 1603 +p '
82 Command submissions are bounded by a write() system call.
83 Multiple commands can be written together, separated by ``;`` or ``\n``::
85 :#> ddcmd "func pnpacpi_get_resources +p; func pnp_assign_mem +p"
87 func pnpacpi_get_resources +p
88 func pnp_assign_mem +p
90 :#> cat query-batch-file > /proc/dynamic_debug/control
92 You can also use wildcards in each query term. The match rule supports
93 ``*`` (matches zero or more characters) and ``?`` (matches exactly one
94 character). For example, you can match all usb drivers::
96 :#> ddcmd file "drivers/usb/*" +p # "" to suppress shell expansion
98 Syntactically, a command is pairs of keyword values, followed by a
99 flags change or setting::
101 command ::= match-spec* flags-spec
103 The match-spec's select *prdbgs* from the catalog, upon which to apply
104 the flags-spec, all constraints are ANDed together. An absent keyword
105 is the same as keyword "*".
108 A match specification is a keyword, which selects the attribute of
109 the callsite to be compared, and a value to compare against. Possible
112 match-spec ::= 'func' string |
119 line-range ::= lineno |
124 lineno ::= unsigned-int
128 ``line-range`` cannot contain space, e.g.
129 "1-30" is valid range but "1 - 30" is not.
132 The meanings of each keyword are:
135 The given string is compared against the function name
136 of each callsite. Example::
139 func *recv* # in rfcomm, bluetooth, ping, tcp
142 The given string is compared against either the src-root relative
143 pathname, or the basename of the source file of each callsite.
147 file kernel/freezer.c # ie column 1 of control file
148 file drivers/usb/* # all callsites under it
149 file inode.c:start_* # parse :tail as a func (above)
150 file inode.c:1-100 # parse :tail as a line-range (above)
153 The given string is compared against the module name
154 of each callsite. The module name is the string as
155 seen in ``lsmod``, i.e. without the directory or the ``.ko``
156 suffix and with ``-`` changed to ``_``. Examples::
160 module drm* # both drm, drm_kms_helper
163 The given string is searched for in the dynamic debug format
164 string. Note that the string does not need to match the
165 entire format, only some part. Whitespace and other
166 special characters can be escaped using C octal character
167 escape ``\ooo`` notation, e.g. the space character is ``\040``.
168 Alternatively, the string can be enclosed in double quote
169 characters (``"``) or single quote characters (``'``).
172 format svcrdma: // many of the NFS/RDMA server pr_debugs
173 format readahead // some pr_debugs in the readahead cache
174 format nfsd:\040SETATTR // one way to match a format with whitespace
175 format "nfsd: SETATTR" // a neater way to match a format with whitespace
176 format 'nfsd: SETATTR' // yet another way to match a format with whitespace
179 The given class_name is validated against each module, which may
180 have declared a list of known class_names. If the class_name is
181 found for a module, callsite & class matching and adjustment
184 class DRM_UT_KMS # a DRM.debug category
185 class JUNK # silent non-match
186 // class TLD_* # NOTICE: no wildcard in class names
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 last line number means the
195 last line number in the file. Examples::
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
202 The flags specification comprises a change operation followed
203 by one or more flag characters. The change operation is one
206 - remove the given flags
207 + add the given flags
208 = set the flags to the given flags
212 p enables the pr_debug() callsite.
215 Decorator flags add to the message-prefix, in order:
216 t Include thread ID, or <intr>
217 m Include module name
218 f Include the function name
219 l Include line number
221 For ``print_hex_dump_debug()`` and ``print_hex_dump_bytes()``, only
222 the ``p`` flag has meaning, other flags are ignored.
224 Note the regexp ``^[-+=][flmpt_]+$`` matches a flags specification.
225 To clear all flags at once, use ``=_`` or ``-flmpt``.
228 Debug messages during Boot Process
229 ==================================
231 To activate debug messages for core code and built-in modules during
232 the boot process, even before userspace and debugfs exists, use
233 ``dyndbg="QUERY"`` or ``module.dyndbg="QUERY"``. QUERY follows
234 the syntax described above, but must not exceed 1023 characters. Your
235 bootloader may impose lower limits.
237 These ``dyndbg`` params are processed just after the ddebug tables are
238 processed, as part of the early_initcall. Thus you can enable debug
239 messages in all code run after this early_initcall via this boot
242 On an x86 system for example ACPI enablement is a subsys_initcall and::
244 dyndbg="file ec.c +p"
246 will show early Embedded Controller transactions during ACPI setup if
247 your machine (typically a laptop) has an Embedded Controller.
248 PCI (or other devices) initialization also is a hot candidate for using
249 this boot parameter for debugging purposes.
251 If ``foo`` module is not built-in, ``foo.dyndbg`` will still be processed at
252 boot time, without effect, but will be reprocessed when module is
253 loaded later. Bare ``dyndbg=`` is only processed at boot.
256 Debug Messages at Module Initialization Time
257 ============================================
259 When ``modprobe foo`` is called, modprobe scans ``/proc/cmdline`` for
260 ``foo.params``, strips ``foo.``, and passes them to the kernel along with
261 params given in modprobe args or ``/etc/modprob.d/*.conf`` files,
262 in the following order:
264 1. parameters given via ``/etc/modprobe.d/*.conf``::
266 options foo dyndbg=+pt
267 options foo dyndbg # defaults to +p
269 2. ``foo.dyndbg`` as given in boot args, ``foo.`` is stripped and passed::
271 foo.dyndbg=" func bar +p; func buz +mp"
273 3. args to modprobe::
275 modprobe foo dyndbg==pmf # override previous settings
277 These ``dyndbg`` queries are applied in order, with last having final say.
278 This allows boot args to override or modify those from ``/etc/modprobe.d``
279 (sensible, since 1 is system wide, 2 is kernel or boot specific), and
280 modprobe args to override both.
282 In the ``foo.dyndbg="QUERY"`` form, the query must exclude ``module foo``.
283 ``foo`` is extracted from the param-name, and applied to each query in
284 ``QUERY``, and only 1 match-spec of each type is allowed.
286 The ``dyndbg`` option is a "fake" module parameter, which means:
288 - modules do not need to define it explicitly
289 - every module gets it tacitly, whether they use pr_debug or not
290 - it doesn't appear in ``/sys/module/$module/parameters/``
291 To see it, grep the control file, or inspect ``/proc/cmdline.``
293 For ``CONFIG_DYNAMIC_DEBUG`` kernels, any settings given at boot-time (or
294 enabled by ``-DDEBUG`` flag during compilation) can be disabled later via
295 the debugfs interface if the debug messages are no longer needed::
297 echo "module module_name -p" > /proc/dynamic_debug/control
304 // enable the message at line 1603 of file svcsock.c
305 :#> ddcmd 'file svcsock.c line 1603 +p'
307 // enable all the messages in file svcsock.c
308 :#> ddcmd 'file svcsock.c +p'
310 // enable all the messages in the NFS server module
311 :#> ddcmd 'module nfsd +p'
313 // enable all 12 messages in the function svc_process()
314 :#> ddcmd 'func svc_process +p'
316 // disable all 12 messages in the function svc_process()
317 :#> ddcmd 'func svc_process -p'
319 // enable messages for NFS calls READ, READLINK, READDIR and READDIR+.
320 :#> ddcmd 'format "nfsd: READ" +p'
322 // enable messages in files of which the paths include string "usb"
323 :#> ddcmd 'file *usb* +p' > /proc/dynamic_debug/control
325 // enable all messages
326 :#> ddcmd '+p' > /proc/dynamic_debug/control
328 // add module, function to all enabled messages
329 :#> ddcmd '+mf' > /proc/dynamic_debug/control
331 // boot-args example, with newlines and comments for readability
332 Kernel command line: ...
333 // see what's going on in dyndbg=value processing
334 dynamic_debug.verbose=3
335 // enable pr_debugs in the btrfs module (can be builtin or loadable)
337 // enable pr_debugs in all files under init/
338 // and the function parse_one, #cmt is stripped
339 dyndbg="file init/* +p #cmt ; func parse_one +p"
340 // enable pr_debugs in 2 functions in a module loaded later
341 pc87360.dyndbg="func pc87360_init_device +p; func pc87360_find +p"
346 Dynamic Debug is enabled via kernel config items::
348 CONFIG_DYNAMIC_DEBUG=y # build catalog, enables CORE
349 CONFIG_DYNAMIC_DEBUG_CORE=y # enable mechanics only, skip catalog
351 If you do not want to enable dynamic debug globally (i.e. in some embedded
352 system), you may set ``CONFIG_DYNAMIC_DEBUG_CORE`` as basic support of dynamic
353 debug and add ``ccflags := -DDYNAMIC_DEBUG_MODULE`` into the Makefile of any
354 modules which you'd like to dynamically debug later.
360 The following functions are cataloged and controllable when dynamic
365 print_hex_dump_debug()
366 print_hex_dump_bytes()
368 Otherwise, they are off by default; ``ccflags += -DDEBUG`` or
369 ``#define DEBUG`` in a source file will enable them appropriately.
371 If ``CONFIG_DYNAMIC_DEBUG`` is not set, ``print_hex_dump_debug()`` is
372 just a shortcut for ``print_hex_dump(KERN_DEBUG)``.
374 For ``print_hex_dump_debug()``/``print_hex_dump_bytes()``, format string is
375 its ``prefix_str`` argument, if it is constant string; or ``hexdump``
376 in case ``prefix_str`` is built dynamically.