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Subject[PATCH 18/25] dynamic_debug: Introduce global fake module param $module.dyndbg
Date
From: Jim Cromie <jim.cromie@gmail.com>

Rework Thomas Renninger's $module.ddebug boot-time debugging feature,
from https://lkml.org/lkml/2010/9/15/397

Extend dynamic-debug facility to work during module initialization:

foo.dyndbg bar.dyndbg="$bar-query-string"

This patch introduces a 'fake' module parameter: $module.ddebug for
all modules. It is not explicitly added to each module, but is
implemented as an unknown-parameter callback invoked by kernel/param's
parse_one(), and it applies each module's query-string as if it were
written to the $DBGFS/dynamic_debug/control file.

The module-name is added to the unknown-parameter callback signature
and to its caller: parse_one(). This lets the common callback know
what module its handling a common parameter for.

If no value is given (as in foo.dyndbg example above), "+p" is
assumed, which enables all pr_debug callsites in the module.

The parameter is not shown in /sys/module/*/parameters, thus it does
not use any resources. Changes to the parameter are made via the
control file.

Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
CC: Thomas Renninger <trenn@suse.de>
CC: Rusty Russell <rusty@rustcorp.com.au>
---
Documentation/dynamic-debug-howto.txt | 52 ++++++++++++++++++++++++++++++++-
include/linux/dynamic_debug.h | 11 +++++++
include/linux/moduleparam.h | 2 +-
init/main.c | 7 ++--
kernel/module.c | 3 +-
kernel/params.c | 10 ++++--
lib/dynamic_debug.c | 16 +++++++++-
7 files changed, 89 insertions(+), 12 deletions(-)

diff --git a/Documentation/dynamic-debug-howto.txt b/Documentation/dynamic-debug-howto.txt
index 989a892..56e496a 100644
--- a/Documentation/dynamic-debug-howto.txt
+++ b/Documentation/dynamic-debug-howto.txt
@@ -219,7 +219,7 @@ Note also that there is no convenient syntax to remove all
the flags at once, you need to use "-flmpt".


-Debug messages during boot process
+Debug messages during Boot Process
==================================

To be able to activate debug messages during the boot process,
@@ -238,6 +238,45 @@ PCI (or other devices) initialization also is a hot candidate for using
this boot parameter for debugging purposes.


+Debug Messages at Module Initialization Time
+============================================
+
+Enabling a module's debug messages via debug control file only works
+once the module is loaded; too late for callsites in init functions.
+And when module is unloaded, debug flag settings for the module are
+lost. Instead, a "dyndbg" module parameter can be passed:
+
+ - via kernel boot parameter: (this form works on built-ins too)
+ module.dyndbg=+mfp
+ module.dyndbg # defaults to +p
+
+ - as an ordinary module parameter via modprobe
+ modprobe module dyndbg=+pmfl
+ modprobe module dyndbg # defaults to +p
+
+ - or the parameter can be used permanently via modprobe.conf(.local)
+ options module dyndbg=+pmflt
+ options module dyndbg # defaults to +p
+
+The $modname.dyndbg="value" should exclude "module $modname", as the
+$modname is taken from the param-name, and only 1 spec of each type is
+allowed.
+
+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
+debug messages are no longer needed:
+
+ echo "module module_name -p" > <debugfs>/dynamic_debug/control
+
+$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.
+
Examples
========

@@ -264,3 +303,14 @@ nullarbor:~ # echo -n 'func svc_process -p' >
// enable messages for NFS calls READ, READLINK, READDIR and READDIR+.
nullarbor:~ # echo -n 'format "nfsd: READ" +p' >
<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
+ k10temp.dyndbg="+p # comment in query is stripped "
+ pnp.dyndbg="func pnpacpi_get_resources +p; func pnp_assign_mem +p" # multi
diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index 7e3c53a..b77f43b 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h
@@ -39,11 +39,16 @@ struct _ddebug {
int ddebug_add_module(struct _ddebug *tab, unsigned int n,
const char *modname);

+struct kernel_param;
+
#if defined(CONFIG_DYNAMIC_DEBUG)
extern int ddebug_remove_module(const char *mod_name);
+
extern __printf(2, 3)
int __dynamic_pr_debug(struct _ddebug *descriptor, const char *fmt, ...);

+extern int ddebug_dyndbg_param_cb(char *param, char *val, const char *modname);
+
struct device;

extern __printf(3, 4)
@@ -99,6 +104,12 @@ static inline int ddebug_remove_module(const char *mod)
return 0;
}

+static inline int ddebug_dyndbg_param_cb(char *param, char *val, const char *modname)
+{
+ pr_warn("dyndbg supported only in CONFIG_DYNAMIC_DEBUG builds\n");
+ return 0; /* dont fail modprobe, warning is enough */
+}
+
#define dynamic_pr_debug(fmt, ...) \
do { if (0) printk(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__); } while (0)
#define dynamic_dev_dbg(dev, fmt, ...) \
diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
index 7939f63..91bd56a 100644
--- a/include/linux/moduleparam.h
+++ b/include/linux/moduleparam.h
@@ -292,7 +292,7 @@ extern int parse_args(const char *name,
char *args,
const struct kernel_param *params,
unsigned num,
- int (*unknown)(char *param, char *val));
+ int (*unknown)(char *param, char *val, const char *modname));

/* Called by module remove. */
#ifdef CONFIG_SYSFS
diff --git a/init/main.c b/init/main.c
index 217ed23..4a591ec 100644
--- a/init/main.c
+++ b/init/main.c
@@ -230,7 +230,7 @@ early_param("loglevel", loglevel);
* Unknown boot options get handed to init, unless they look like
* unused parameters (modprobe will find them in /proc/cmdline).
*/
-static int __init unknown_bootoption(char *param, char *val)
+static int __init unknown_bootoption(char *param, char *val, const char *modname)
{
/* Change NUL term back to "=", to make "param" the whole string. */
if (val) {
@@ -387,7 +387,7 @@ static noinline void __init_refok rest_init(void)
}

/* Check for early params. */
-static int __init do_early_param(char *param, char *val)
+static int __init do_early_param(char *param, char *val, const char *modname)
{
const struct obs_kernel_param *p;

@@ -510,8 +510,7 @@ asmlinkage void __init start_kernel(void)
printk(KERN_NOTICE "Kernel command line: %s\n", boot_command_line);
parse_early_param();
parse_args("Booting kernel", static_command_line, __start___param,
- __stop___param - __start___param,
- &unknown_bootoption);
+ __stop___param - __start___param, &unknown_bootoption);

jump_label_init();

diff --git a/kernel/module.c b/kernel/module.c
index 30ffed4..c7b495e 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2893,7 +2893,8 @@ static struct module *load_module(void __user *umod,
mutex_unlock(&module_mutex);

/* Module is ready to execute: parsing args may do that. */
- err = parse_args(mod->name, mod->args, mod->kp, mod->num_kp, NULL);
+ err = parse_args(mod->name, mod->args, mod->kp, mod->num_kp,
+ ddebug_dyndbg_param_cb);
if (err < 0)
goto unlink;

diff --git a/kernel/params.c b/kernel/params.c
index 65aae11..70a9878 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -92,9 +92,11 @@ bool parameq(const char *a, const char *b)

static int parse_one(char *param,
char *val,
+ const char *modname,
const struct kernel_param *params,
unsigned num_params,
- int (*handle_unknown)(char *param, char *val))
+ int (*handle_unknown)(char *param, char *val,
+ const char *modname))
{
unsigned int i;
int err;
@@ -116,7 +118,7 @@ static int parse_one(char *param,

if (handle_unknown) {
DEBUGP("Unknown argument: calling %p\n", handle_unknown);
- return handle_unknown(param, val);
+ return handle_unknown(param, val, modname);
}

DEBUGP("Unknown argument `%s'\n", param);
@@ -180,7 +182,7 @@ int parse_args(const char *name,
char *args,
const struct kernel_param *params,
unsigned num,
- int (*unknown)(char *param, char *val))
+ int (*unknown)(char *param, char *val, const char *modname))
{
char *param, *val;

@@ -195,7 +197,7 @@ int parse_args(const char *name,

args = next_arg(args, &param, &val);
irq_was_disabled = irqs_disabled();
- ret = parse_one(param, val, params, num, unknown);
+ ret = parse_one(param, val, name, params, num, unknown);
if (irq_was_disabled && !irqs_disabled()) {
printk(KERN_WARNING "parse_args(): option '%s' enabled "
"irq's!\n", param);
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index 516ad4e..b774849 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -618,7 +618,7 @@ static __initdata char ddebug_setup_string[DDEBUG_STRING_SIZE];

static __init int ddebug_setup_query(char *str)
{
- if (strlen(str) >= 1024) {
+ if (strlen(str) >= DDEBUG_STRING_SIZE) {
pr_warn("ddebug boot param string too large\n");
return 0;
}
@@ -872,6 +872,20 @@ int ddebug_add_module(struct _ddebug *tab, unsigned int n,
}
EXPORT_SYMBOL_GPL(ddebug_add_module);

+int ddebug_dyndbg_param_cb(char *param, char* val, const char* modname)
+{
+ if (strcmp(param, "dyndbg")) {
+ pr_warn("bogus param %s=%s received for %s\n",
+ param, val, modname);
+ return -EINVAL;
+ }
+ if (verbose)
+ pr_info("module: %s %s=\"%s\"\n", modname, param, val);
+
+ ddebug_exec_queries((val ? val : "+p"));
+ return 0; /* query failure shouldnt stop module load */
+}
+
static void ddebug_table_free(struct ddebug_table *dt)
{
list_del_init(&dt->link);
--
1.7.7.3


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