loglevel 7 (debug) and pr_debug()

[Valdis.Kletnieks at vt.edu]

On Wed, 16 Apr 2014 13:57:07 +0200, Martin Kepplinger said:

> I'd like to just read all pr_debug() messages like pr_info().

Did you consider, um, I don't know? Just building a kernel that
doesn't have CONFIG_DYNAMIC_DEBUG turned on?

Or you could read Documentation/dynamic-debug-howto.txt, and find this:

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


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