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Subject[PATCH 23/25] dynamic_debug: update Documentation/kernel-parameters.txt, Kconfig.debug
From: Jim Cromie <>

In kernel-parameters.txt:

- update flags indicators in example output, from '-' to '=_'.
- add sentence on _ flag-char
- more info in Module Initialization section
$module.dyndbg, *.dyndbg

In Kconfig.debug, note enabled-by-default effect of -DDEBUG

Signed-off-by: Jim Cromie <>
Documentation/dynamic-debug-howto.txt | 52 ++++++++++++++++++++++-----------
Documentation/kernel-parameters.txt | 9 ++++++
lib/Kconfig.debug | 15 ++++++----
3 files changed, 53 insertions(+), 23 deletions(-)

diff --git a/Documentation/dynamic-debug-howto.txt b/Documentation/dynamic-debug-howto.txt
index 56e496a..2a9da50 100644
--- a/Documentation/dynamic-debug-howto.txt
+++ b/Documentation/dynamic-debug-howto.txt
@@ -49,10 +49,10 @@ 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"

@@ -70,7 +70,7 @@ 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:

-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"

@@ -213,10 +213,11 @@ p
Causes a printk() message to be emitted to dmesg
Include thread ID in messages not generated from interrupt context
+ No flags are set

-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
@@ -237,6 +238,8 @@ 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.

+Note: ddebug_query= is supplanted by the feature in the next section,
+and will be deprecated later.

Debug Messages at Module Initialization Time
@@ -258,10 +261,16 @@ lost. Instead, a "dyndbg" module parameter can be passed:
options module dyndbg=+pmflt
options module dyndbg # defaults to +p

-The $modname.dyndbg="value" should exclude "module $modname", as the
+The $modname.dyndbg="value" must exclude "module $modname", as the
$modname is taken from the param-name, and only 1 spec of each type is

+*.dyndbg="+p" can be used to enable all builtin (only) debug
+callsites, or to set print-format defaults (="+mf") for those enabled
+separately. Loadable modules are not affected by wildcard rules, the
+module loader selects only boot options whose module name matches that
+being loaded.
The dyndbg option is not implemented as an ordinary module parameter
and thus will not show up in /sys/module/module_name/parameters/dyndbg
The settings can be reverted later via the sysfs interface if the
@@ -273,9 +282,12 @@ $module.dyndbg="..." on boot-line works on built-in modules as well as
those loaded by modprobe (from either early or normal userspace), and
somewhat overlaps debug_query functionality.

-Modprobed modules get dyndbg flags given on boot-line after those
-given via modprobe (either explicitly, or from /etc/modprobe.d/*).
-This can surprise if boot-line arg subtracts flags.
+When a module is loaded, dyndbg flags are applied in following order,
+with last having final say:
+ - as given in /etc/modprobe.d/* system-wide settings
+ - as given on boot-line kernel, boot-time specific
+ - as given in modprobe command explicit at load

@@ -304,13 +316,19 @@ nullarbor:~ # echo -n 'func svc_process -p' >
nullarbor:~ # echo -n 'format "nfsd: READ" +p' >

+// 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
Kernel command line: ...
ddebug_query="func i2c_del_adapter +p; func tboot_probe +p"
- dynamic_debug.verbose=1 // see whats going on
- nouveau.dyndbg // implicit =+p
- tsc_sync.dyndbg=+p // builtin on my kernel
- i2c_core.dyndbg=+p // loaded by udev
- *.dyndbg="=_" // wildcard applies to builtins
+ dynamic_debug.verbose=1 // see whats going on
+ nouveau.dyndbg // implicit =+p
+ tsc_sync.dyndbg=+p // builtin on my kernel
+ i2c_core.dyndbg=+p // loaded by udev
+ *.dyndbg="+mf" // print module, function for enabled sites
k10temp.dyndbg="+p # comment in query is stripped "
pnp.dyndbg="func pnpacpi_get_resources +p; func pnp_assign_mem +p" # multi
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 81c27b1..387443d 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -691,6 +691,15 @@ bytes respectively. Such letter suffixes can also be entirely omitted.

dscc4.setup= [NET]

+ $modulename.dyndbg[=string]
+ [KNL,DYNAMIC_DEBUG] Enable debug messages in
+ $modulename for builtin or loadable modules. Debug
+ during module initialization is supported.
+ These parameters are not exposed in
+ /sys/module/${modnm}/parameters/dyndbg.
+ See Documentation/dynamic-debug-howto.txt for
+ details of allowed strings, etc.
earlycon= [KNL] Output early console device and options.
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 82928f5..f6fbd92 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1184,8 +1184,11 @@ config DYNAMIC_DEBUG
otherwise be available at runtime. These messages can then be
enabled/disabled based on various levels of scope - per source file,
function, module, format string, and line number. This mechanism
- implicitly enables all pr_debug() and dev_dbg() calls. The impact of
- this compile option is a larger kernel text size of about 2%.
+ implicitly compiles in all pr_debug() and dev_dbg() calls, which
+ enlarges the kernel text size by about 2%.
+ If a source file is compiled with DEBUG flag set, any pr_debug()
+ calls in it are enabled by default, but can be disabled as below.


@@ -1202,16 +1205,16 @@ config DYNAMIC_DEBUG
lineno : line number of the debug statement
module : module that contains the debug statement
function : function that contains the debug statement
- flags : 'p' means the line is turned 'on' for printing
+ flags : '=p' means the line is turned 'on' for printing
format : the format used for the debug statement

From a live system:

nullarbor:~ # cat <debugfs>/dynamic_debug/control
# filename:lineno [module]function flags format
- fs/aio.c:222 [aio]__put_ioctx - "__put_ioctx:\040freeing\040%p\012"
- fs/aio.c:248 [aio]ioctx_alloc - "ENOMEM:\040nr_events\040too\040high\012"
- fs/aio.c:1770 [aio]sys_io_cancel - "calling\040cancel\012"
+ fs/aio.c:222 [aio]__put_ioctx =_ "__put_ioctx:\040freeing\040%p\012"
+ fs/aio.c:248 [aio]ioctx_alloc =_ "ENOMEM:\040nr_events\040too\040high\012"
+ fs/aio.c:1770 [aio]sys_io_cancel =_ "calling\040cancel\012"

Example usage:


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