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>

1 files changed, 31 insertions, 0 deletions

diff --git a/kernel/module.c b/kernel/module.c
index d5fcd24e5aff..c52700667292 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -784,6 +784,7 @@ sys_delete_module(const char __user *name_user, unsigned int flags)
         mutex_lock(&module_mutex);
         /* Store the name of the last unloaded module for diagnostic purposes */
         strlcpy(last_unloaded_module, mod->name, sizeof(last_unloaded_module));
+        unregister_dynamic_debug_module(mod->name);
         free_module(mod);
 
  out:
@@ -1783,6 +1784,33 @@ static inline void add_kallsyms(struct module *mod,
 }
 #endif /* CONFIG_KALLSYMS */
 
+#ifdef CONFIG_DYNAMIC_PRINTK_DEBUG
+static void dynamic_printk_setup(Elf_Shdr *sechdrs, unsigned int verboseindex)
+{
+        struct mod_debug *debug_info;
+        unsigned long pos, end;
+        unsigned int num_verbose;
+
+        pos = sechdrs[verboseindex].sh_addr;
+        num_verbose = sechdrs[verboseindex].sh_size /
+                                sizeof(struct mod_debug);
+        end = pos + (num_verbose * sizeof(struct mod_debug));
+
+        for (; pos < end; pos += sizeof(struct mod_debug)) {
+                debug_info = (struct mod_debug *)pos;
+                register_dynamic_debug_module(debug_info->modname,
+                        debug_info->type, debug_info->logical_modname,
+                        debug_info->flag_names, debug_info->hash,
+                        debug_info->hash2);
+        }
+}
+#else
+static inline void dynamic_printk_setup(Elf_Shdr *sechdrs,
+                                        unsigned int verboseindex)
+{
+}
+#endif /* CONFIG_DYNAMIC_PRINTK_DEBUG */
+
 static void *module_alloc_update_bounds(unsigned long size)
 {
         void *ret = module_alloc(size);
@@ -1831,6 +1859,7 @@ static noinline struct module *load_module(void __user *umod,
 #endif
         unsigned int markersindex;
         unsigned int markersstringsindex;
+        unsigned int verboseindex;
         struct module *mod;
         long err = 0;
         void *percpu = NULL, *ptr = NULL; /* Stops spurious gcc warning */
@@ -2117,6 +2146,7 @@ static noinline struct module *load_module(void __user *umod,
         markersindex = find_sec(hdr, sechdrs, secstrings, "__markers");
         markersstringsindex = find_sec(hdr, sechdrs, secstrings,
                                         "__markers_strings");
+        verboseindex = find_sec(hdr, sechdrs, secstrings, "__verbose");
 
         /* Now do relocations. */
         for (i = 1; i < hdr->e_shnum; i++) {
@@ -2167,6 +2197,7 @@ static noinline struct module *load_module(void __user *umod,
                 marker_update_probe_range(mod->markers,
                         mod->markers + mod->num_markers);
 #endif
+        dynamic_printk_setup(sechdrs, verboseindex);
         err = module_finalize(hdr, sechdrs, mod);
         if (err < 0)
                 goto cleanup;