1Dynamic debug 2+++++++++++++ 3 4 5Introduction 6============ 7 8Dynamic debug allows you to dynamically enable/disable kernel 9debug-print code to obtain additional kernel information. 10 11If ``/proc/dynamic_debug/control`` exists, your kernel has dynamic 12debug. You'll need root access (sudo su) to use this. 13 14Dynamic debug provides: 15 16 * a Catalog of all *prdbgs* in your kernel. 17 ``cat /proc/dynamic_debug/control`` to see them. 18 19 * a Simple query/command language to alter *prdbgs* by selecting on 20 any combination of 0 or 1 of: 21 22 - source filename 23 - function name 24 - line number (including ranges of line numbers) 25 - module name 26 - format string 27 - class name (as known/declared by each module) 28 29Viewing Dynamic Debug Behaviour 30=============================== 31 32You can view the currently configured behaviour in the *prdbg* catalog:: 33 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" 42 43The 3rd space-delimited column shows the current flags, preceded by 44a ``=`` for easy use with grep/cut. ``=p`` shows enabled callsites. 45 46Controlling dynamic debug Behaviour 47=================================== 48 49The behaviour of *prdbg* sites are controlled by writing 50query/commands to the control file. Example:: 51 52 # grease the interface 53 :#> alias ddcmd='echo $* > /proc/dynamic_debug/control' 54 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" 61 62Error messages go to console/syslog:: 63 64 :#> ddcmd mode foo +p 65 dyndbg: unknown keyword "mode" 66 dyndbg: query parse failed 67 bash: echo: write error: Invalid argument 68 69If debugfs is also enabled and mounted, ``dynamic_debug/control`` is 70also under the mount-dir, typically ``/sys/kernel/debug/``. 71 72Command Language Reference 73========================== 74 75At the basic lexical level, a command is a sequence of words separated 76by spaces or tabs. So these are all equivalent:: 77 78 :#> ddcmd file svcsock.c line 1603 +p 79 :#> ddcmd "file svcsock.c line 1603 +p" 80 :#> ddcmd ' file svcsock.c line 1603 +p ' 81 82Command submissions are bounded by a write() system call. 83Multiple commands can be written together, separated by ``;`` or ``\n``:: 84 85 :#> ddcmd "func pnpacpi_get_resources +p; func pnp_assign_mem +p" 86 :#> ddcmd <<"EOC" 87 func pnpacpi_get_resources +p 88 func pnp_assign_mem +p 89 EOC 90 :#> cat query-batch-file > /proc/dynamic_debug/control 91 92You can also use wildcards in each query term. The match rule supports 93``*`` (matches zero or more characters) and ``?`` (matches exactly one 94character). For example, you can match all usb drivers:: 95 96 :#> ddcmd file "drivers/usb/*" +p # "" to suppress shell expansion 97 98Syntactically, a command is pairs of keyword values, followed by a 99flags change or setting:: 100 101 command ::= match-spec* flags-spec 102 103The match-spec's select *prdbgs* from the catalog, upon which to apply 104the flags-spec, all constraints are ANDed together. An absent keyword 105is the same as keyword "*". 106 107 108A match specification is a keyword, which selects the attribute of 109the callsite to be compared, and a value to compare against. Possible 110keywords are::: 111 112 match-spec ::= 'func' string | 113 'file' string | 114 'module' string | 115 'format' string | 116 'class' string | 117 'line' line-range 118 119 line-range ::= lineno | 120 '-'lineno | 121 lineno'-' | 122 lineno'-'lineno 123 124 lineno ::= unsigned-int 125 126.. note:: 127 128 ``line-range`` cannot contain space, e.g. 129 "1-30" is valid range but "1 - 30" is not. 130 131 132The meanings of each keyword are: 133 134func 135 The given string is compared against the function name 136 of each callsite. Example:: 137 138 func svc_tcp_accept 139 func *recv* # in rfcomm, bluetooth, ping, tcp 140 141file 142 The given string is compared against either the src-root relative 143 pathname, or the basename of the source file of each callsite. 144 Examples:: 145 146 file svcsock.c 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) 151 152module 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:: 157 158 module sunrpc 159 module nfsd 160 module drm* # both drm, drm_kms_helper 161 162format 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 (``'``). 170 Examples:: 171 172 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 177 178class 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 182 proceeds. Examples:: 183 184 class DRM_UT_KMS # a DRM.debug category 185 class JUNK # silent non-match 186 // class TLD_* # NOTICE: no wildcard in class names 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 last line number means the 195 last line 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 _ enables no flags. 214 215 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 220 221For ``print_hex_dump_debug()`` and ``print_hex_dump_bytes()``, only 222the ``p`` flag has meaning, other flags are ignored. 223 224Note the regexp ``^[-+=][flmpt_]+$`` matches a flags specification. 225To clear all flags at once, use ``=_`` or ``-flmpt``. 226 227 228Debug messages during Boot Process 229================================== 230 231To activate debug messages for core code and built-in modules during 232the boot process, even before userspace and debugfs exists, use 233``dyndbg="QUERY"`` or ``module.dyndbg="QUERY"``. QUERY follows 234the syntax described above, but must not exceed 1023 characters. Your 235bootloader may impose lower limits. 236 237These ``dyndbg`` params are processed just after the ddebug tables are 238processed, as part of the early_initcall. Thus you can enable debug 239messages in all code run after this early_initcall via this boot 240parameter. 241 242On an x86 system for example ACPI enablement is a subsys_initcall and:: 243 244 dyndbg="file ec.c +p" 245 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. Bare ``dyndbg=`` is only processed at boot. 254 255 256Debug Messages at Module Initialization Time 257============================================ 258 259When ``modprobe foo`` is called, modprobe scans ``/proc/cmdline`` for 260``foo.params``, strips ``foo.``, and passes them to the kernel along with 261params given in modprobe args or ``/etc/modprob.d/*.conf`` files, 262in the following order: 263 2641. parameters given via ``/etc/modprobe.d/*.conf``:: 265 266 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:: 270 271 foo.dyndbg=" func bar +p; func buz +mp" 272 2733. args to modprobe:: 274 275 modprobe foo dyndbg==pmf # override previous settings 276 277These ``dyndbg`` queries are applied in order, with last having final say. 278This 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 280modprobe args to override both. 281 282In 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. 285 286The ``dyndbg`` option is a "fake" module parameter, which means: 287 288- 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.`` 292 293For ``CONFIG_DYNAMIC_DEBUG`` kernels, any settings given at boot-time (or 294enabled by ``-DDEBUG`` flag during compilation) can be disabled later via 295the debugfs interface if the debug messages are no longer needed:: 296 297 echo "module module_name -p" > /proc/dynamic_debug/control 298 299Examples 300======== 301 302:: 303 304 // enable the message at line 1603 of file svcsock.c 305 :#> ddcmd 'file svcsock.c line 1603 +p' 306 307 // enable all the messages in file svcsock.c 308 :#> ddcmd 'file svcsock.c +p' 309 310 // enable all the messages in the NFS server module 311 :#> ddcmd 'module nfsd +p' 312 313 // enable all 12 messages in the function svc_process() 314 :#> ddcmd 'func svc_process +p' 315 316 // disable all 12 messages in the function svc_process() 317 :#> ddcmd 'func svc_process -p' 318 319 // enable messages for NFS calls READ, READLINK, READDIR and READDIR+. 320 :#> ddcmd 'format "nfsd: READ" +p' 321 322 // enable messages in files of which the paths include string "usb" 323 :#> ddcmd 'file *usb* +p' > /proc/dynamic_debug/control 324 325 // enable all messages 326 :#> ddcmd '+p' > /proc/dynamic_debug/control 327 328 // add module, function to all enabled messages 329 :#> ddcmd '+mf' > /proc/dynamic_debug/control 330 331 // boot-args example, with newlines and comments for readability 332 Kernel command line: ... 333 // see whats going on in dyndbg=value processing 334 dynamic_debug.verbose=3 335 // enable pr_debugs in the btrfs module (can be builtin or loadable) 336 btrfs.dyndbg="+p" 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" 342 343Kernel Configuration 344==================== 345 346Dynamic Debug is enabled via kernel config items:: 347 348 CONFIG_DYNAMIC_DEBUG=y # build catalog, enables CORE 349 CONFIG_DYNAMIC_DEBUG_CORE=y # enable mechanics only, skip catalog 350 351If you do not want to enable dynamic debug globally (i.e. in some embedded 352system), you may set ``CONFIG_DYNAMIC_DEBUG_CORE`` as basic support of dynamic 353debug and add ``ccflags := -DDYNAMIC_DEBUG_MODULE`` into the Makefile of any 354modules which you'd like to dynamically debug later. 355 356 357Kernel *prdbg* API 358================== 359 360The following functions are cataloged and controllable when dynamic 361debug is enabled:: 362 363 pr_debug() 364 dev_dbg() 365 print_hex_dump_debug() 366 print_hex_dump_bytes() 367 368Otherwise, they are off by default; ``ccflags += -DDEBUG`` or 369``#define DEBUG`` in a source file will enable them appropriately. 370 371If ``CONFIG_DYNAMIC_DEBUG`` is not set, ``print_hex_dump_debug()`` is 372just a shortcut for ``print_hex_dump(KERN_DEBUG)``. 373 374For ``print_hex_dump_debug()``/``print_hex_dump_bytes()``, format string is 375its ``prefix_str`` argument, if it is constant string; or ``hexdump`` 376in case ``prefix_str`` is built dynamically. 377