Introduction
============
-This document describes how to use the dynamic debug (ddebug) feature.
+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 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:
+ * Simple query language allows turning on and off debugging
+ statements by matching any combination of 0 or 1 of:
- source filename
- function name
- 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
+ * 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:
+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
Viewing Dynamic Debug Behaviour
===========================
-You can view the currently configured behaviour of all the debug statements
-via:
+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"
+/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"
...
nullarbor:~ # grep -i tcp <debugfs>/dynamic_debug/control | wc -l
42
-Note in particular that the third column shows the enabled behaviour
-flags for each debug statement callsite (see below for definitions of the
-flags). The default value, no extra behaviour enabled, is "-". So
-you can view all the debug statement callsites with any non-default flags:
+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
+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 ::= match-spec* flags-spec
-The match-spec's are used to choose a subset of the known dprintk()
+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 is possible, but is not very useful because it will not
-match any debug statement callsites.
+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:
+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 |
characters (") or single quote characters (').
Examples:
- format svcrdma: // many of the NFS/RDMA server dprintks
- format readahead // some dprintks in the readahead cache
+ 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 dprintk() callsite. A single
+ 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
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
+ - remove the given flags
+ + add the given flags
+ = set the flags to the given flags
The flags are:
-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
-p
- Causes a printk() message to be emitted to dmesg
-t
- Include thread ID in messages not generated from interrupt context
+ 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.
-Note also that there is no convenient syntax to remove all
-the flags at once, you need to use "-flmpt".
+Note the regexp ^[-+=][flmpt_]+$ matches a flags specification.
+To clear all flags at once, use "=_" or "-flmpt".
-Debug messages during boot process
+Debug messages during Boot Process
==================================
-To be able to activate debug messages during the boot process,
-even before userspace and debugfs exists, use the boot parameter:
-ddebug_query="QUERY"
+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.
-QUERY follows the syntax described above, but must not exceed 1023
-characters. The enablement of debug messages is done as an arch_initcall.
-Thus you can enable debug messages in all code processed after this
-arch_initcall via this boot parameter.
On an x86 system for example ACPI enablement is a subsys_initcall and
-ddebug_query="file ec.c +p"
+ 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 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"
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