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-
-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() calls can
-be dynamically enabled per-callsite.
-
-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
-
-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 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 doesnt 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 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"