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diff --git a/Documentation/dynamic-debug-howto.txt b/Documentation/dynamic-debug-howto.txt new file mode 100644 index 000000000..9417871b8 --- /dev/null +++ b/Documentation/dynamic-debug-howto.txt @@ -0,0 +1,340 @@ + +Introduction +============ + +This document describes how to use the dynamic debug (dyndbg) feature. + +Dynamic debug is designed to allow you to dynamically enable/disable +kernel code to obtain additional kernel information. Currently, if +CONFIG_DYNAMIC_DEBUG is set, then all pr_debug()/dev_dbg() and +print_hex_dump_debug()/print_hex_dump_bytes() calls can be dynamically +enabled per-callsite. + +If CONFIG_DYNAMIC_DEBUG is not set, print_hex_dump_debug() is just +shortcut for print_hex_dump(KERN_DEBUG). + +For print_hex_dump_debug()/print_hex_dump_bytes(), format string is +its 'prefix_str' argument, if it is constant string; or "hexdump" +in case 'prefix_str' is build dynamically. + +Dynamic debug has even more useful features: + + * Simple query language allows turning on and off debugging + statements by matching any combination of 0 or 1 of: + + - source filename + - function name + - line number (including ranges of line numbers) + - module name + - format string + + * Provides a debugfs control file: <debugfs>/dynamic_debug/control + which can be read to display the complete list of known debug + statements, to help guide you + +Controlling dynamic debug Behaviour +=================================== + +The behaviour of pr_debug()/dev_dbg()s are controlled via writing to a +control file in the 'debugfs' filesystem. Thus, you must first mount +the debugfs filesystem, in order to make use of this feature. +Subsequently, we refer to the control file as: +<debugfs>/dynamic_debug/control. For example, if you want to enable +printing from source file 'svcsock.c', line 1603 you simply do: + +nullarbor:~ # echo 'file svcsock.c line 1603 +p' > + <debugfs>/dynamic_debug/control + +If you make a mistake with the syntax, the write will fail thus: + +nullarbor:~ # echo 'file svcsock.c wtf 1 +p' > + <debugfs>/dynamic_debug/control +-bash: echo: write error: Invalid argument + +Viewing Dynamic Debug Behaviour +=========================== + +You can view the currently configured behaviour of all the debug +statements via: + +nullarbor:~ # cat <debugfs>/dynamic_debug/control +# filename:lineno [module]function flags format +/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" +/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:341 [svcxprt_rdma]svc_rdma_init =_ "\011max_inline : %d\012" +/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:340 [svcxprt_rdma]svc_rdma_init =_ "\011sq_depth : %d\012" +/usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:338 [svcxprt_rdma]svc_rdma_init =_ "\011max_requests : %d\012" +... + + +You can also apply standard Unix text manipulation filters to this +data, e.g. + +nullarbor:~ # grep -i rdma <debugfs>/dynamic_debug/control | wc -l +62 + +nullarbor:~ # grep -i tcp <debugfs>/dynamic_debug/control | wc -l +42 + +The third column shows the currently enabled flags for each debug +statement callsite (see below for definitions of the flags). The +default value, with no flags enabled, is "=_". So you can view all +the debug statement callsites with any non-default flags: + +nullarbor:~ # awk '$3 != "=_"' <debugfs>/dynamic_debug/control +# filename:lineno [module]function flags format +/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" + + +Command Language Reference +========================== + +At the lexical level, a command comprises a sequence of words separated +by spaces or tabs. So these are all equivalent: + +nullarbor:~ # echo -c 'file svcsock.c line 1603 +p' > + <debugfs>/dynamic_debug/control +nullarbor:~ # echo -c ' file svcsock.c line 1603 +p ' > + <debugfs>/dynamic_debug/control +nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' > + <debugfs>/dynamic_debug/control + +Command submissions are bounded by a write() system call. +Multiple commands can be written together, separated by ';' or '\n'. + + ~# echo "func pnpacpi_get_resources +p; func pnp_assign_mem +p" \ + > <debugfs>/dynamic_debug/control + +If your query set is big, you can batch them too: + + ~# cat query-batch-file > <debugfs>/dynamic_debug/control + +A another way is to use wildcard. The match rule support '*' (matches +zero or more characters) and '?' (matches exactly one character).For +example, you can match all usb drivers: + + ~# echo "file drivers/usb/* +p" > <debugfs>/dynamic_debug/control + +At the syntactical level, a command comprises a sequence of match +specifications, followed by a flags change specification. + +command ::= match-spec* flags-spec + +The match-spec's are used to choose a subset of the known pr_debug() +callsites to which to apply the flags-spec. Think of them as a query +with implicit ANDs between each pair. Note that an empty list of +match-specs will select all debug statement callsites. + +A match specification comprises a keyword, which controls the +attribute of the callsite to be compared, and a value to compare +against. Possible keywords are: + +match-spec ::= 'func' string | + 'file' string | + 'module' string | + 'format' string | + 'line' line-range + +line-range ::= lineno | + '-'lineno | + lineno'-' | + lineno'-'lineno +// Note: line-range cannot contain space, e.g. +// "1-30" is valid range but "1 - 30" is not. + +lineno ::= unsigned-int + +The meanings of each keyword are: + +func + The given string is compared against the function name + of each callsite. Example: + + func svc_tcp_accept + +file + The given string is compared against either the full pathname, the + src-root relative pathname, or the basename of the source file of + each callsite. Examples: + + file svcsock.c + file kernel/freezer.c + file /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svcsock.c + +module + The given string is compared against the module name + of each callsite. The module name is the string as + seen in "lsmod", i.e. without the directory or the .ko + suffix and with '-' changed to '_'. Examples: + + module sunrpc + module nfsd + +format + The given string is searched for in the dynamic debug format + string. Note that the string does not need to match the + entire format, only some part. Whitespace and other + special characters can be escaped using C octal character + escape \ooo notation, e.g. the space character is \040. + Alternatively, the string can be enclosed in double quote + characters (") or single quote characters ('). + Examples: + + format svcrdma: // many of the NFS/RDMA server pr_debugs + format readahead // some pr_debugs in the readahead cache + format nfsd:\040SETATTR // one way to match a format with whitespace + format "nfsd: SETATTR" // a neater way to match a format with whitespace + format 'nfsd: SETATTR' // yet another way to match a format with whitespace + +line + The given line number or range of line numbers is compared + against the line number of each pr_debug() callsite. A single + line number matches the callsite line number exactly. A + range of line numbers matches any callsite between the first + and last line number inclusive. An empty first number means + the first line in the file, an empty line number means the + last number in the file. Examples: + + line 1603 // exactly line 1603 + line 1600-1605 // the six lines from line 1600 to line 1605 + line -1605 // the 1605 lines from line 1 to line 1605 + line 1600- // all lines from line 1600 to the end of the file + +The flags specification comprises a change operation followed +by one or more flag characters. The change operation is one +of the characters: + + - remove the given flags + + add the given flags + = set the flags to the given flags + +The flags are: + + p enables the pr_debug() callsite. + f Include the function name in the printed message + l Include line number in the printed message + m Include module name in the printed message + t Include thread ID in messages not generated from interrupt context + _ No flags are set. (Or'd with others on input) + +For print_hex_dump_debug() and print_hex_dump_bytes(), only 'p' flag +have meaning, other flags ignored. + +For display, the flags are preceded by '=' +(mnemonic: what the flags are currently equal to). + +Note the regexp ^[-+=][flmpt_]+$ matches a flags specification. +To clear all flags at once, use "=_" or "-flmpt". + + +Debug messages during Boot Process +================================== + +To activate debug messages for core code and built-in modules during +the boot process, even before userspace and debugfs exists, use +dyndbg="QUERY", module.dyndbg="QUERY", or ddebug_query="QUERY" +(ddebug_query is obsoleted by dyndbg, and deprecated). QUERY follows +the syntax described above, but must not exceed 1023 characters. Your +bootloader may impose lower limits. + +These dyndbg params are processed just after the ddebug tables are +processed, as part of the arch_initcall. Thus you can enable debug +messages in all code run after this arch_initcall via this boot +parameter. + +On an x86 system for example ACPI enablement is a subsys_initcall and + dyndbg="file ec.c +p" +will show early Embedded Controller transactions during ACPI setup if +your machine (typically a laptop) has an Embedded Controller. +PCI (or other devices) initialization also is a hot candidate for using +this boot parameter for debugging purposes. + +If foo module is not built-in, foo.dyndbg will still be processed at +boot time, without effect, but will be reprocessed when module is +loaded later. dyndbg_query= and bare dyndbg= are only processed at +boot. + + +Debug Messages at Module Initialization Time +============================================ + +When "modprobe foo" is called, modprobe scans /proc/cmdline for +foo.params, strips "foo.", and passes them to the kernel along with +params given in modprobe args or /etc/modprob.d/*.conf files, +in the following order: + +1. # parameters given via /etc/modprobe.d/*.conf + options foo dyndbg=+pt + options foo dyndbg # defaults to +p + +2. # foo.dyndbg as given in boot args, "foo." is stripped and passed + foo.dyndbg=" func bar +p; func buz +mp" + +3. # args to modprobe + modprobe foo dyndbg==pmf # override previous settings + +These dyndbg queries are applied in order, with last having final say. +This allows boot args to override or modify those from /etc/modprobe.d +(sensible, since 1 is system wide, 2 is kernel or boot specific), and +modprobe args to override both. + +In the foo.dyndbg="QUERY" form, the query must exclude "module foo". +"foo" is extracted from the param-name, and applied to each query in +"QUERY", and only 1 match-spec of each type is allowed. + +The dyndbg option is a "fake" module parameter, which means: + +- modules do not need to define it explicitly +- every module gets it tacitly, whether they use pr_debug or not +- it doesn't appear in /sys/module/$module/parameters/ + To see it, grep the control file, or inspect /proc/cmdline. + +For CONFIG_DYNAMIC_DEBUG kernels, any settings given at boot-time (or +enabled by -DDEBUG flag during compilation) can be disabled later via +the sysfs interface if the debug messages are no longer needed: + + echo "module module_name -p" > <debugfs>/dynamic_debug/control + +Examples +======== + +// enable the message at line 1603 of file svcsock.c +nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' > + <debugfs>/dynamic_debug/control + +// enable all the messages in file svcsock.c +nullarbor:~ # echo -n 'file svcsock.c +p' > + <debugfs>/dynamic_debug/control + +// enable all the messages in the NFS server module +nullarbor:~ # echo -n 'module nfsd +p' > + <debugfs>/dynamic_debug/control + +// enable all 12 messages in the function svc_process() +nullarbor:~ # echo -n 'func svc_process +p' > + <debugfs>/dynamic_debug/control + +// disable all 12 messages in the function svc_process() +nullarbor:~ # echo -n 'func svc_process -p' > + <debugfs>/dynamic_debug/control + +// enable messages for NFS calls READ, READLINK, READDIR and READDIR+. +nullarbor:~ # echo -n 'format "nfsd: READ" +p' > + <debugfs>/dynamic_debug/control + +// enable messages in files of which the paths include string "usb" +nullarbor:~ # echo -n '*usb* +p' > <debugfs>/dynamic_debug/control + +// enable all messages +nullarbor:~ # echo -n '+p' > <debugfs>/dynamic_debug/control + +// add module, function to all enabled messages +nullarbor:~ # echo -n '+mf' > <debugfs>/dynamic_debug/control + +// boot-args example, with newlines and comments for readability +Kernel command line: ... + // see whats going on in dyndbg=value processing + dynamic_debug.verbose=1 + // enable pr_debugs in 2 builtins, #cmt is stripped + dyndbg="module params +p #cmt ; module sys +p" + // enable pr_debugs in 2 functions in a module loaded later + pc87360.dyndbg="func pc87360_init_device +p; func pc87360_find +p" |