1Dynamic debug 2+++++++++++++ 3 4 5Introduction 6============ 7 8This document describes how to use the dynamic debug (dyndbg) feature. 9 10Dynamic debug is designed to allow you to dynamically enable/disable 11kernel code to obtain additional kernel information. Currently, if 12``CONFIG_DYNAMIC_DEBUG`` is set, then all ``pr_debug()``/``dev_dbg()`` and 13``print_hex_dump_debug()``/``print_hex_dump_bytes()`` calls can be dynamically 14enabled per-callsite. 15 16If ``CONFIG_DYNAMIC_DEBUG`` is not set, ``print_hex_dump_debug()`` is just 17shortcut for ``print_hex_dump(KERN_DEBUG)``. 18 19For ``print_hex_dump_debug()``/``print_hex_dump_bytes()``, format string is 20its ``prefix_str`` argument, if it is constant string; or ``hexdump`` 21in case ``prefix_str`` is build dynamically. 22 23Dynamic debug has even more useful features: 24 25 * Simple query language allows turning on and off debugging 26 statements by matching any combination of 0 or 1 of: 27 28 - source filename 29 - function name 30 - line number (including ranges of line numbers) 31 - module name 32 - format string 33 34 * Provides a debugfs control file: ``<debugfs>/dynamic_debug/control`` 35 which can be read to display the complete list of known debug 36 statements, to help guide you 37 38Controlling dynamic debug Behaviour 39=================================== 40 41The behaviour of ``pr_debug()``/``dev_dbg()`` are controlled via writing to a 42control file in the 'debugfs' filesystem. Thus, you must first mount 43the debugfs filesystem, in order to make use of this feature. 44Subsequently, we refer to the control file as: 45``<debugfs>/dynamic_debug/control``. For example, if you want to enable 46printing from source file ``svcsock.c``, line 1603 you simply do:: 47 48 nullarbor:~ # echo 'file svcsock.c line 1603 +p' > 49 <debugfs>/dynamic_debug/control 50 51If you make a mistake with the syntax, the write will fail thus:: 52 53 nullarbor:~ # echo 'file svcsock.c wtf 1 +p' > 54 <debugfs>/dynamic_debug/control 55 -bash: echo: write error: Invalid argument 56 57Viewing Dynamic Debug Behaviour 58=============================== 59 60You can view the currently configured behaviour of all the debug 61statements via:: 62 63 nullarbor:~ # cat <debugfs>/dynamic_debug/control 64 # filename:lineno [module]function flags format 65 /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" 66 /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:341 [svcxprt_rdma]svc_rdma_init =_ "\011max_inline : %d\012" 67 /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:340 [svcxprt_rdma]svc_rdma_init =_ "\011sq_depth : %d\012" 68 /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:338 [svcxprt_rdma]svc_rdma_init =_ "\011max_requests : %d\012" 69 ... 70 71 72You can also apply standard Unix text manipulation filters to this 73data, e.g.:: 74 75 nullarbor:~ # grep -i rdma <debugfs>/dynamic_debug/control | wc -l 76 62 77 78 nullarbor:~ # grep -i tcp <debugfs>/dynamic_debug/control | wc -l 79 42 80 81The third column shows the currently enabled flags for each debug 82statement callsite (see below for definitions of the flags). The 83default value, with no flags enabled, is ``=_``. So you can view all 84the debug statement callsites with any non-default flags:: 85 86 nullarbor:~ # awk '$3 != "=_"' <debugfs>/dynamic_debug/control 87 # filename:lineno [module]function flags format 88 /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" 89 90Command Language Reference 91========================== 92 93At the lexical level, a command comprises a sequence of words separated 94by spaces or tabs. So these are all equivalent:: 95 96 nullarbor:~ # echo -c 'file svcsock.c line 1603 +p' > 97 <debugfs>/dynamic_debug/control 98 nullarbor:~ # echo -c ' file svcsock.c line 1603 +p ' > 99 <debugfs>/dynamic_debug/control 100 nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' > 101 <debugfs>/dynamic_debug/control 102 103Command submissions are bounded by a write() system call. 104Multiple commands can be written together, separated by ``;`` or ``\n``:: 105 106 ~# echo "func pnpacpi_get_resources +p; func pnp_assign_mem +p" \ 107 > <debugfs>/dynamic_debug/control 108 109If your query set is big, you can batch them too:: 110 111 ~# cat query-batch-file > <debugfs>/dynamic_debug/control 112 113A another way is to use wildcard. The match rule support ``*`` (matches 114zero or more characters) and ``?`` (matches exactly one character).For 115example, you can match all usb drivers:: 116 117 ~# echo "file drivers/usb/* +p" > <debugfs>/dynamic_debug/control 118 119At the syntactical level, a command comprises a sequence of match 120specifications, followed by a flags change specification:: 121 122 command ::= match-spec* flags-spec 123 124The match-spec's are used to choose a subset of the known pr_debug() 125callsites to which to apply the flags-spec. Think of them as a query 126with implicit ANDs between each pair. Note that an empty list of 127match-specs will select all debug statement callsites. 128 129A match specification comprises a keyword, which controls the 130attribute of the callsite to be compared, and a value to compare 131against. Possible keywords are::: 132 133 match-spec ::= 'func' string | 134 'file' string | 135 'module' string | 136 'format' string | 137 'line' line-range 138 139 line-range ::= lineno | 140 '-'lineno | 141 lineno'-' | 142 lineno'-'lineno 143 144 lineno ::= unsigned-int 145 146.. note:: 147 148 ``line-range`` cannot contain space, e.g. 149 "1-30" is valid range but "1 - 30" is not. 150 151 152The meanings of each keyword are: 153 154func 155 The given string is compared against the function name 156 of each callsite. Example:: 157 158 func svc_tcp_accept 159 160file 161 The given string is compared against either the full pathname, the 162 src-root relative pathname, or the basename of the source file of 163 each callsite. Examples:: 164 165 file svcsock.c 166 file kernel/freezer.c 167 file /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svcsock.c 168 169module 170 The given string is compared against the module name 171 of each callsite. The module name is the string as 172 seen in ``lsmod``, i.e. without the directory or the ``.ko`` 173 suffix and with ``-`` changed to ``_``. Examples:: 174 175 module sunrpc 176 module nfsd 177 178format 179 The given string is searched for in the dynamic debug format 180 string. Note that the string does not need to match the 181 entire format, only some part. Whitespace and other 182 special characters can be escaped using C octal character 183 escape ``\ooo`` notation, e.g. the space character is ``\040``. 184 Alternatively, the string can be enclosed in double quote 185 characters (``"``) or single quote characters (``'``). 186 Examples:: 187 188 format svcrdma: // many of the NFS/RDMA server pr_debugs 189 format readahead // some pr_debugs in the readahead cache 190 format nfsd:\040SETATTR // one way to match a format with whitespace 191 format "nfsd: SETATTR" // a neater way to match a format with whitespace 192 format 'nfsd: SETATTR' // yet another way to match a format with whitespace 193 194line 195 The given line number or range of line numbers is compared 196 against the line number of each ``pr_debug()`` callsite. A single 197 line number matches the callsite line number exactly. A 198 range of line numbers matches any callsite between the first 199 and last line number inclusive. An empty first number means 200 the first line in the file, an empty line number means the 201 last number in the file. Examples:: 202 203 line 1603 // exactly line 1603 204 line 1600-1605 // the six lines from line 1600 to line 1605 205 line -1605 // the 1605 lines from line 1 to line 1605 206 line 1600- // all lines from line 1600 to the end of the file 207 208The flags specification comprises a change operation followed 209by one or more flag characters. The change operation is one 210of the characters:: 211 212 - remove the given flags 213 + add the given flags 214 = set the flags to the given flags 215 216The flags are:: 217 218 p enables the pr_debug() callsite. 219 f Include the function name in the printed message 220 l Include line number in the printed message 221 m Include module name in the printed message 222 t Include thread ID in messages not generated from interrupt context 223 _ No flags are set. (Or'd with others on input) 224 225For ``print_hex_dump_debug()`` and ``print_hex_dump_bytes()``, only ``p`` flag 226have meaning, other flags ignored. 227 228For display, the flags are preceded by ``=`` 229(mnemonic: what the flags are currently equal to). 230 231Note the regexp ``^[-+=][flmpt_]+$`` matches a flags specification. 232To clear all flags at once, use ``=_`` or ``-flmpt``. 233 234 235Debug messages during Boot Process 236================================== 237 238To activate debug messages for core code and built-in modules during 239the boot process, even before userspace and debugfs exists, use 240``dyndbg="QUERY"``, ``module.dyndbg="QUERY"``, or ``ddebug_query="QUERY"`` 241(``ddebug_query`` is obsoleted by ``dyndbg``, and deprecated). QUERY follows 242the syntax described above, but must not exceed 1023 characters. Your 243bootloader may impose lower limits. 244 245These ``dyndbg`` params are processed just after the ddebug tables are 246processed, as part of the arch_initcall. Thus you can enable debug 247messages in all code run after this arch_initcall via this boot 248parameter. 249 250On an x86 system for example ACPI enablement is a subsys_initcall and:: 251 252 dyndbg="file ec.c +p" 253 254will show early Embedded Controller transactions during ACPI setup if 255your machine (typically a laptop) has an Embedded Controller. 256PCI (or other devices) initialization also is a hot candidate for using 257this boot parameter for debugging purposes. 258 259If ``foo`` module is not built-in, ``foo.dyndbg`` will still be processed at 260boot time, without effect, but will be reprocessed when module is 261loaded later. ``dyndbg_query=`` and bare ``dyndbg=`` are only processed at 262boot. 263 264 265Debug Messages at Module Initialization Time 266============================================ 267 268When ``modprobe foo`` is called, modprobe scans ``/proc/cmdline`` for 269``foo.params``, strips ``foo.``, and passes them to the kernel along with 270params given in modprobe args or ``/etc/modprob.d/*.conf`` files, 271in the following order: 272 2731. parameters given via ``/etc/modprobe.d/*.conf``:: 274 275 options foo dyndbg=+pt 276 options foo dyndbg # defaults to +p 277 2782. ``foo.dyndbg`` as given in boot args, ``foo.`` is stripped and passed:: 279 280 foo.dyndbg=" func bar +p; func buz +mp" 281 2823. args to modprobe:: 283 284 modprobe foo dyndbg==pmf # override previous settings 285 286These ``dyndbg`` queries are applied in order, with last having final say. 287This allows boot args to override or modify those from ``/etc/modprobe.d`` 288(sensible, since 1 is system wide, 2 is kernel or boot specific), and 289modprobe args to override both. 290 291In the ``foo.dyndbg="QUERY"`` form, the query must exclude ``module foo``. 292``foo`` is extracted from the param-name, and applied to each query in 293``QUERY``, and only 1 match-spec of each type is allowed. 294 295The ``dyndbg`` option is a "fake" module parameter, which means: 296 297- modules do not need to define it explicitly 298- every module gets it tacitly, whether they use pr_debug or not 299- it doesn't appear in ``/sys/module/$module/parameters/`` 300 To see it, grep the control file, or inspect ``/proc/cmdline.`` 301 302For ``CONFIG_DYNAMIC_DEBUG`` kernels, any settings given at boot-time (or 303enabled by ``-DDEBUG`` flag during compilation) can be disabled later via 304the sysfs interface if the debug messages are no longer needed:: 305 306 echo "module module_name -p" > <debugfs>/dynamic_debug/control 307 308Examples 309======== 310 311:: 312 313 // enable the message at line 1603 of file svcsock.c 314 nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' > 315 <debugfs>/dynamic_debug/control 316 317 // enable all the messages in file svcsock.c 318 nullarbor:~ # echo -n 'file svcsock.c +p' > 319 <debugfs>/dynamic_debug/control 320 321 // enable all the messages in the NFS server module 322 nullarbor:~ # echo -n 'module nfsd +p' > 323 <debugfs>/dynamic_debug/control 324 325 // enable all 12 messages in the function svc_process() 326 nullarbor:~ # echo -n 'func svc_process +p' > 327 <debugfs>/dynamic_debug/control 328 329 // disable all 12 messages in the function svc_process() 330 nullarbor:~ # echo -n 'func svc_process -p' > 331 <debugfs>/dynamic_debug/control 332 333 // enable messages for NFS calls READ, READLINK, READDIR and READDIR+. 334 nullarbor:~ # echo -n 'format "nfsd: READ" +p' > 335 <debugfs>/dynamic_debug/control 336 337 // enable messages in files of which the paths include string "usb" 338 nullarbor:~ # echo -n '*usb* +p' > <debugfs>/dynamic_debug/control 339 340 // enable all messages 341 nullarbor:~ # echo -n '+p' > <debugfs>/dynamic_debug/control 342 343 // add module, function to all enabled messages 344 nullarbor:~ # echo -n '+mf' > <debugfs>/dynamic_debug/control 345 346 // boot-args example, with newlines and comments for readability 347 Kernel command line: ... 348 // see whats going on in dyndbg=value processing 349 dynamic_debug.verbose=1 350 // enable pr_debugs in 2 builtins, #cmt is stripped 351 dyndbg="module params +p #cmt ; module sys +p" 352 // enable pr_debugs in 2 functions in a module loaded later 353 pc87360.dyndbg="func pc87360_init_device +p; func pc87360_find +p" 354