driver core: basic infrastructure for per-module dynamic debug messages

Base infrastructure to enable per-module debug messages.

I've introduced CONFIG_DYNAMIC_PRINTK_DEBUG, which when enabled centralizes
control of debugging statements on a per-module basis in one /proc file,
currently, <debugfs>/dynamic_printk/modules. When, CONFIG_DYNAMIC_PRINTK_DEBUG,
is not set, debugging statements can still be enabled as before, often by
defining 'DEBUG' for the proper compilation unit. Thus, this patch set has no
affect when CONFIG_DYNAMIC_PRINTK_DEBUG is not set.

The infrastructure currently ties into all pr_debug() and dev_dbg() calls. That
is, if CONFIG_DYNAMIC_PRINTK_DEBUG is set, all pr_debug() and dev_dbg() calls
can be dynamically enabled/disabled on a per-module basis.

Future plans include extending this functionality to subsystems, that define 
their own debug levels and flags.

Usage:

Dynamic debugging is controlled by the debugfs file, 
<debugfs>/dynamic_printk/modules. This file contains a list of the modules that
can be enabled. The format of the file is as follows:

	<module_name> <enabled=0/1>
		.
		.
		.

	<module_name> : Name of the module in which the debug call resides
	<enabled=0/1> : whether the messages are enabled or not

For example:

	snd_hda_intel enabled=0
	fixup enabled=1
	driver enabled=0

Enable a module:

	$echo "set enabled=1 <module_name>" > dynamic_printk/modules

Disable a module:

	$echo "set enabled=0 <module_name>" > dynamic_printk/modules

Enable all modules:

	$echo "set enabled=1 all" > dynamic_printk/modules

Disable all modules:

	$echo "set enabled=0 all" > dynamic_printk/modules

Finally, passing "dynamic_printk" at the command line enables
debugging for all modules. This mode can be turned off via the above
disable command.

[gkh: minor cleanups and tweaks to make the build work quietly]

Signed-off-by: Jason Baron <jbaron@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

2 files changed, 65 insertions, 1 deletions

diff --git a/scripts/basic/Makefile b/scripts/basic/Makefile
index 4c324a1f1e0e..09559951df12 100644
--- a/scripts/basic/Makefile
+++ b/scripts/basic/Makefile
@@ -9,7 +9,7 @@
 # fixdep:        Used to generate dependency information during build process
 # docproc:       Used in Documentation/DocBook
 
-hostprogs-y     := fixdep docproc
+hostprogs-y     := fixdep docproc hash
 always          := $(hostprogs-y)
 
 # fixdep is needed to compile other host programs
diff --git a/scripts/basic/hash.c b/scripts/basic/hash.c
new file mode 100644
index 000000000000..3299ad7fc8c0
--- /dev/null
+++ b/scripts/basic/hash.c
@@ -0,0 +1,64 @@
+/*
+ * Copyright (C) 2008 Red Hat, Inc., Jason Baron <jbaron@redhat.com>
+ *
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define DYNAMIC_DEBUG_HASH_BITS 6
+
+static const char *program;
+
+static void usage(void)
+{
+        printf("Usage: %s <djb2|r5> <modname>\n", program);
+        exit(1);
+}
+
+/* djb2 hashing algorithm by Dan Bernstein. From:
+ * http://www.cse.yorku.ca/~oz/hash.html
+ */
+
+unsigned int djb2_hash(char *str)
+{
+        unsigned long hash = 5381;
+        int c;
+
+        c = *str;
+        while (c) {
+                hash = ((hash << 5) + hash) + c;
+                c = *++str;
+        }
+        return (unsigned int)(hash & ((1 << DYNAMIC_DEBUG_HASH_BITS) - 1));
+}
+
+unsigned int r5_hash(char *str)
+{
+        unsigned long hash = 0;
+        int c;
+
+        c = *str;
+        while (c) {
+                hash = (hash + (c << 4) + (c >> 4)) * 11;
+                c = *++str;
+        }
+        return (unsigned int)(hash & ((1 << DYNAMIC_DEBUG_HASH_BITS) - 1));
+}
+
+int main(int argc, char *argv[])
+{
+        program = argv[0];
+
+        if (argc != 3)
+                usage();
+        if (!strcmp(argv[1], "djb2"))
+                printf("%d\n", djb2_hash(argv[2]));
+        else if (!strcmp(argv[1], "r5"))
+                printf("%d\n", r5_hash(argv[2]));
+        else
+                usage();
+        exit(0);
+}
+