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 you do not want to enable dynamic debug globally (i.e. in some embedded 17system), you may set ``CONFIG_DYNAMIC_DEBUG_CORE`` as basic support of dynamic 18debug and add ``ccflags := -DDYNAMIC_DEBUG_MODULE`` into the Makefile of any 19modules which you'd like to dynamically debug later. 20 21If ``CONFIG_DYNAMIC_DEBUG`` is not set, ``print_hex_dump_debug()`` is just 22shortcut for ``print_hex_dump(KERN_DEBUG)``. 23 24For ``print_hex_dump_debug()``/``print_hex_dump_bytes()``, format string is 25its ``prefix_str`` argument, if it is constant string; or ``hexdump`` 26in case ``prefix_str`` is built dynamically. 27 28Dynamic debug has even more useful features: 29 30 * Simple query language allows turning on and off debugging 31 statements by matching any combination of 0 or 1 of: 32 33 - source filename 34 - function name 35 - line number (including ranges of line numbers) 36 - module name 37 - format string 38 39 * Provides a debugfs control file: ``<debugfs>/dynamic_debug/control`` 40 which can be read to display the complete list of known debug 41 statements, to help guide you 42 43Controlling dynamic debug Behaviour 44=================================== 45 46The behaviour of ``pr_debug()``/``dev_dbg()`` are controlled via writing to a 47control file in the 'debugfs' filesystem. Thus, you must first mount 48the debugfs filesystem, in order to make use of this feature. 49Subsequently, we refer to the control file as: 50``<debugfs>/dynamic_debug/control``. For example, if you want to enable 51printing from source file ``svcsock.c``, line 1603 you simply do:: 52 53 nullarbor:~ # echo 'file svcsock.c line 1603 +p' > 54 <debugfs>/dynamic_debug/control 55 56If you make a mistake with the syntax, the write will fail thus:: 57 58 nullarbor:~ # echo 'file svcsock.c wtf 1 +p' > 59 <debugfs>/dynamic_debug/control 60 -bash: echo: write error: Invalid argument 61 62Note, for systems without 'debugfs' enabled, the control file can be 63found in ``/proc/dynamic_debug/control``. 64 65Viewing Dynamic Debug Behaviour 66=============================== 67 68You can view the currently configured behaviour of all the debug 69statements via:: 70 71 nullarbor:~ # cat <debugfs>/dynamic_debug/control 72 # filename:lineno [module]function flags format 73 net/sunrpc/svc_rdma.c:323 [svcxprt_rdma]svc_rdma_cleanup =_ "SVCRDMA Module Removed, deregister RPC RDMA transport\012" 74 net/sunrpc/svc_rdma.c:341 [svcxprt_rdma]svc_rdma_init =_ "\011max_inline : %d\012" 75 net/sunrpc/svc_rdma.c:340 [svcxprt_rdma]svc_rdma_init =_ "\011sq_depth : %d\012" 76 net/sunrpc/svc_rdma.c:338 [svcxprt_rdma]svc_rdma_init =_ "\011max_requests : %d\012" 77 ... 78 79 80You can also apply standard Unix text manipulation filters to this 81data, e.g.:: 82 83 nullarbor:~ # grep -i rdma <debugfs>/dynamic_debug/control | wc -l 84 62 85 86 nullarbor:~ # grep -i tcp <debugfs>/dynamic_debug/control | wc -l 87 42 88 89The third column shows the currently enabled flags for each debug 90statement callsite (see below for definitions of the flags). The 91default value, with no flags enabled, is ``=_``. So you can view all 92the debug statement callsites with any non-default flags:: 93 94 nullarbor:~ # awk '$3 != "=_"' <debugfs>/dynamic_debug/control 95 # filename:lineno [module]function flags format 96 net/sunrpc/svcsock.c:1603 [sunrpc]svc_send p "svc_process: st_sendto returned %d\012" 97 98Command Language Reference 99========================== 100 101At the lexical level, a command comprises a sequence of words separated 102by spaces or tabs. So these are all equivalent:: 103 104 nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' > 105 <debugfs>/dynamic_debug/control 106 nullarbor:~ # echo -n ' file svcsock.c line 1603 +p ' > 107 <debugfs>/dynamic_debug/control 108 nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' > 109 <debugfs>/dynamic_debug/control 110 111Command submissions are bounded by a write() system call. 112Multiple commands can be written together, separated by ``;`` or ``\n``:: 113 114 ~# echo "func pnpacpi_get_resources +p; func pnp_assign_mem +p" \ 115 > <debugfs>/dynamic_debug/control 116 117If your query set is big, you can batch them too:: 118 119 ~# cat query-batch-file > <debugfs>/dynamic_debug/control 120 121Another way is to use wildcards. The match rule supports ``*`` (matches 122zero or more characters) and ``?`` (matches exactly one character). For 123example, you can match all usb drivers:: 124 125 ~# echo "file drivers/usb/* +p" > <debugfs>/dynamic_debug/control 126 127At the syntactical level, a command comprises a sequence of match 128specifications, followed by a flags change specification:: 129 130 command ::= match-spec* flags-spec 131 132The match-spec's are used to choose a subset of the known pr_debug() 133callsites to which to apply the flags-spec. Think of them as a query 134with implicit ANDs between each pair. Note that an empty list of 135match-specs will select all debug statement callsites. 136 137A match specification comprises a keyword, which controls the 138attribute of the callsite to be compared, and a value to compare 139against. Possible keywords are::: 140 141 match-spec ::= 'func' string | 142 'file' string | 143 'module' string | 144 'format' string | 145 'line' line-range 146 147 line-range ::= lineno | 148 '-'lineno | 149 lineno'-' | 150 lineno'-'lineno 151 152 lineno ::= unsigned-int 153 154.. note:: 155 156 ``line-range`` cannot contain space, e.g. 157 "1-30" is valid range but "1 - 30" is not. 158 159 160The meanings of each keyword are: 161 162func 163 The given string is compared against the function name 164 of each callsite. Example:: 165 166 func svc_tcp_accept 167 func *recv* # in rfcomm, bluetooth, ping, tcp 168 169file 170 The given string is compared against either the src-root relative 171 pathname, or the basename of the source file of each callsite. 172 Examples:: 173 174 file svcsock.c 175 file kernel/freezer.c # ie column 1 of control file 176 file drivers/usb/* # all callsites under it 177 file inode.c:start_* # parse :tail as a func (above) 178 file inode.c:1-100 # parse :tail as a line-range (above) 179 180module 181 The given string is compared against the module name 182 of each callsite. The module name is the string as 183 seen in ``lsmod``, i.e. without the directory or the ``.ko`` 184 suffix and with ``-`` changed to ``_``. Examples:: 185 186 module sunrpc 187 module nfsd 188 module drm* # both drm, drm_kms_helper 189 190format 191 The given string is searched for in the dynamic debug format 192 string. Note that the string does not need to match the 193 entire format, only some part. Whitespace and other 194 special characters can be escaped using C octal character 195 escape ``\ooo`` notation, e.g. the space character is ``\040``. 196 Alternatively, the string can be enclosed in double quote 197 characters (``"``) or single quote characters (``'``). 198 Examples:: 199 200 format svcrdma: // many of the NFS/RDMA server pr_debugs 201 format readahead // some pr_debugs in the readahead cache 202 format nfsd:\040SETATTR // one way to match a format with whitespace 203 format "nfsd: SETATTR" // a neater way to match a format with whitespace 204 format 'nfsd: SETATTR' // yet another way to match a format with whitespace 205 206line 207 The given line number or range of line numbers is compared 208 against the line number of each ``pr_debug()`` callsite. A single 209 line number matches the callsite line number exactly. A 210 range of line numbers matches any callsite between the first 211 and last line number inclusive. An empty first number means 212 the first line in the file, an empty last line number means the 213 last line number in the file. Examples:: 214 215 line 1603 // exactly line 1603 216 line 1600-1605 // the six lines from line 1600 to line 1605 217 line -1605 // the 1605 lines from line 1 to line 1605 218 line 1600- // all lines from line 1600 to the end of the file 219 220The flags specification comprises a change operation followed 221by one or more flag characters. The change operation is one 222of the characters:: 223 224 - remove the given flags 225 + add the given flags 226 = set the flags to the given flags 227 228The flags are:: 229 230 p enables the pr_debug() callsite. 231 f Include the function name in the printed message 232 l Include line number in the printed message 233 m Include module name in the printed message 234 t Include thread ID in messages not generated from interrupt context 235 _ No flags are set. (Or'd with others on input) 236 237For ``print_hex_dump_debug()`` and ``print_hex_dump_bytes()``, only ``p`` flag 238have meaning, other flags ignored. 239 240For display, the flags are preceded by ``=`` 241(mnemonic: what the flags are currently equal to). 242 243Note the regexp ``^[-+=][flmpt_]+$`` matches a flags specification. 244To clear all flags at once, use ``=_`` or ``-flmpt``. 245 246 247Debug messages during Boot Process 248================================== 249 250To activate debug messages for core code and built-in modules during 251the boot process, even before userspace and debugfs exists, use 252``dyndbg="QUERY"``, ``module.dyndbg="QUERY"``, or ``ddebug_query="QUERY"`` 253(``ddebug_query`` is obsoleted by ``dyndbg``, and deprecated). QUERY follows 254the syntax described above, but must not exceed 1023 characters. Your 255bootloader may impose lower limits. 256 257These ``dyndbg`` params are processed just after the ddebug tables are 258processed, as part of the early_initcall. Thus you can enable debug 259messages in all code run after this early_initcall via this boot 260parameter. 261 262On an x86 system for example ACPI enablement is a subsys_initcall and:: 263 264 dyndbg="file ec.c +p" 265 266will show early Embedded Controller transactions during ACPI setup if 267your machine (typically a laptop) has an Embedded Controller. 268PCI (or other devices) initialization also is a hot candidate for using 269this boot parameter for debugging purposes. 270 271If ``foo`` module is not built-in, ``foo.dyndbg`` will still be processed at 272boot time, without effect, but will be reprocessed when module is 273loaded later. ``ddebug_query=`` and bare ``dyndbg=`` are only processed at 274boot. 275 276 277Debug Messages at Module Initialization Time 278============================================ 279 280When ``modprobe foo`` is called, modprobe scans ``/proc/cmdline`` for 281``foo.params``, strips ``foo.``, and passes them to the kernel along with 282params given in modprobe args or ``/etc/modprob.d/*.conf`` files, 283in the following order: 284 2851. parameters given via ``/etc/modprobe.d/*.conf``:: 286 287 options foo dyndbg=+pt 288 options foo dyndbg # defaults to +p 289 2902. ``foo.dyndbg`` as given in boot args, ``foo.`` is stripped and passed:: 291 292 foo.dyndbg=" func bar +p; func buz +mp" 293 2943. args to modprobe:: 295 296 modprobe foo dyndbg==pmf # override previous settings 297 298These ``dyndbg`` queries are applied in order, with last having final say. 299This allows boot args to override or modify those from ``/etc/modprobe.d`` 300(sensible, since 1 is system wide, 2 is kernel or boot specific), and 301modprobe args to override both. 302 303In the ``foo.dyndbg="QUERY"`` form, the query must exclude ``module foo``. 304``foo`` is extracted from the param-name, and applied to each query in 305``QUERY``, and only 1 match-spec of each type is allowed. 306 307The ``dyndbg`` option is a "fake" module parameter, which means: 308 309- modules do not need to define it explicitly 310- every module gets it tacitly, whether they use pr_debug or not 311- it doesn't appear in ``/sys/module/$module/parameters/`` 312 To see it, grep the control file, or inspect ``/proc/cmdline.`` 313 314For ``CONFIG_DYNAMIC_DEBUG`` kernels, any settings given at boot-time (or 315enabled by ``-DDEBUG`` flag during compilation) can be disabled later via 316the debugfs interface if the debug messages are no longer needed:: 317 318 echo "module module_name -p" > <debugfs>/dynamic_debug/control 319 320Examples 321======== 322 323:: 324 325 // enable the message at line 1603 of file svcsock.c 326 nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' > 327 <debugfs>/dynamic_debug/control 328 329 // enable all the messages in file svcsock.c 330 nullarbor:~ # echo -n 'file svcsock.c +p' > 331 <debugfs>/dynamic_debug/control 332 333 // enable all the messages in the NFS server module 334 nullarbor:~ # echo -n 'module nfsd +p' > 335 <debugfs>/dynamic_debug/control 336 337 // enable all 12 messages in the function svc_process() 338 nullarbor:~ # echo -n 'func svc_process +p' > 339 <debugfs>/dynamic_debug/control 340 341 // disable all 12 messages in the function svc_process() 342 nullarbor:~ # echo -n 'func svc_process -p' > 343 <debugfs>/dynamic_debug/control 344 345 // enable messages for NFS calls READ, READLINK, READDIR and READDIR+. 346 nullarbor:~ # echo -n 'format "nfsd: READ" +p' > 347 <debugfs>/dynamic_debug/control 348 349 // enable messages in files of which the paths include string "usb" 350 nullarbor:~ # echo -n '*usb* +p' > <debugfs>/dynamic_debug/control 351 352 // enable all messages 353 nullarbor:~ # echo -n '+p' > <debugfs>/dynamic_debug/control 354 355 // add module, function to all enabled messages 356 nullarbor:~ # echo -n '+mf' > <debugfs>/dynamic_debug/control 357 358 // boot-args example, with newlines and comments for readability 359 Kernel command line: ... 360 // see whats going on in dyndbg=value processing 361 dynamic_debug.verbose=1 362 // enable pr_debugs in 2 builtins, #cmt is stripped 363 dyndbg="module params +p #cmt ; module sys +p" 364 // enable pr_debugs in 2 functions in a module loaded later 365 pc87360.dyndbg="func pc87360_init_device +p; func pc87360_find +p" 366