linux-kernel - Re: [PATCH] module interface improvement for kprobes

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Message-Id: <1154721061.15967.31.camel@dhcp-2.hsv.redhat.com>
Date:	Fri, 04 Aug 2006 14:51:01 -0500
From:	David Smith <dsmith@...hat.com>
To:	"Randy.Dunlap" <rdunlap@...otime.net>
Cc:	linux-kernel@...r.kernel.org, rusty@...tcorp.com.au,
	prasanna@...ibm.com, ananth@...ibm.com,
	anil.s.keshavamurthy@...el.com, davem@...emloft.net
Subject: Re: [PATCH] module interface improvement for kprobes

Randy,

Thanks for looking at this.  I implemented your suggestions and also
changed EXPORT_SYMBOL to EXPORT_SYMBOL_GPL.

On Fri, 2006-08-04 at 09:00 -0700, Randy.Dunlap wrote:
> On Fri, 04 Aug 2006 10:17:32 -0500 David Smith wrote:
> 
> > When inserting a kprobes probe into a loadable module, there isn't a way
> > for the kprobes module to get a module reference (in order to find the
> > base address of the module among perhaps other things).
> > 
> > A kprobes probe needs the base address of the module in order to
> > "relocate" the addresses of probe points (since the load address of the
> > module can change from run to run of the kprobe).
> > 
> > I've added a new function, module_get_byname(), that looks up a module
> > by name and returns the module reference.  Note that module_get_byname()
> > also increments the module reference count.  It does this so that the
> > module won't be unloaded between the time that module_get_byname() is
> > called and register_kprobe() is called.

...

Signed off by David Smith <dsmith@...hat.com>

----
diff --git a/include/linux/module.h b/include/linux/module.h
index 0dfb794..9953a38 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -374,6 +374,8 @@ extern void __module_put_and_exit(struct
 	__attribute__((noreturn));
 #define module_put_and_exit(code) __module_put_and_exit(THIS_MODULE,
code);
 
+int module_get_byname(const char *mod_name, struct module **mod);
+
 #ifdef CONFIG_MODULE_UNLOAD
 unsigned int module_refcount(struct module *mod);
 void __symbol_put(const char *symbol);
@@ -549,6 +551,11 @@ static inline int is_exported(const char
 	return 0;
 }
 
+static inline int module_get_byname(const char *mod_name, struct module
**mod)
+{
+	return 1;
+}
+
 static inline int register_module_notifier(struct notifier_block * nb)
 {
 	/* no events will happen anyway, so this can always succeed */
diff --git a/kernel/module.c b/kernel/module.c
index 2a19cd4..473cc0b 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -291,7 +291,27 @@ static struct module *find_module(const 
 	}
 	return NULL;
 }
+  
+int module_get_byname(const char *mod_name, struct module **mod)
+{
+	*mod = NULL;
 
+	/* We must hold module_mutex before calling find_module(). */
+	if (mutex_lock_interruptible(&module_mutex) != 0)
+		return -EINTR;
+
+	*mod = find_module(mod_name);
+	mutex_unlock(&module_mutex);
+	if (*mod) {
+		if (!strong_try_module_get(*mod)) {
+			*mod = NULL;
+			return -EINVAL;
+		}
+	}
+	return 0;
+}
+EXPORT_SYMBOL_GPL(module_get_byname);
+ 
 #ifdef CONFIG_SMP
 /* Number of blocks used and allocated. */
 static unsigned int pcpu_num_used, pcpu_num_allocated;


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