[PATCH 2/6] typesafe: kthread_create and kthread_run

[Rusty Russell <rusty@rustcorp.com.au>]

Simple statement expression with a temporary variable does the
typechecking for us: that the kthread function matches the data type.

If the function doesn't match, we get:

	warning: initialization from incompatible pointer type

It's actually slightly over-strict, since you can hand void * data to
any function callback type, but there's only one such case in the kernel
anyway.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
---
 include/linux/kthread.h |   30 +++++++++++++++++++++++++++---
 kernel/kthread.c        |   29 +++++------------------------
 2 files changed, 32 insertions(+), 27 deletions(-)

diff -r 110aa94129d0 include/linux/kthread.h
--- a/include/linux/kthread.h	Fri Jan 18 10:32:31 2008 +1100
+++ b/include/linux/kthread.h	Fri Jan 18 11:31:49 2008 +1100
@@ -4,9 +4,33 @@
 #include <linux/err.h>
 #include <linux/sched.h>
 
-struct task_struct *kthread_create(int (*threadfn)(void *data),
-				   void *data,
-				   const char namefmt[], ...);
+/**
+ * kthread_create - create a kthread.
+ * @threadfn: the function to run until signal_pending(current).
+ * @data: data ptr for @threadfn.
+ * @namefmt: printf-style name for the thread.
+ *
+ * Description: This helper function creates and names a kernel
+ * thread.  The thread will be stopped: use wake_up_process() to start
+ * it.  See also kthread_run(), kthread_create_on_cpu().
+ *
+ * When woken, the thread will run @threadfn() with @data as its
+ * argument. @threadfn() can either call do_exit() directly if it is a
+ * standalone thread for which noone will call kthread_stop(), or
+ * return when 'kthread_should_stop()' is true (which means
+ * kthread_stop() has been called).  The return value should be zero
+ * or a negative error number; it will be passed to kthread_stop().
+ *
+ * Returns a task_struct or ERR_PTR(-ENOMEM).
+ */
+#define kthread_create(threadfn, data, namefmt...) ({		\
+	int (*_threadfn)(typeof(data)) = (threadfn);		\
+	__kthread_create((void *)_threadfn, (data), namefmt);	\
+})
+
+struct task_struct *__kthread_create(int (*threadfn)(void *data),
+				     void *data,
+				     const char namefmt[], ...);
 
 /**
  * kthread_run - create and wake a thread.
diff -r 110aa94129d0 kernel/kthread.c
--- a/kernel/kthread.c	Fri Jan 18 10:32:31 2008 +1100
+++ b/kernel/kthread.c	Fri Jan 18 11:31:49 2008 +1100
@@ -102,29 +102,10 @@ static void create_kthread(struct kthrea
 	complete(&create->done);
 }
 
-/**
- * kthread_create - create a kthread.
- * @threadfn: the function to run until signal_pending(current).
- * @data: data ptr for @threadfn.
- * @namefmt: printf-style name for the thread.
- *
- * Description: This helper function creates and names a kernel
- * thread.  The thread will be stopped: use wake_up_process() to start
- * it.  See also kthread_run(), kthread_create_on_cpu().
- *
- * When woken, the thread will run @threadfn() with @data as its
- * argument. @threadfn() can either call do_exit() directly if it is a
- * standalone thread for which noone will call kthread_stop(), or
- * return when 'kthread_should_stop()' is true (which means
- * kthread_stop() has been called).  The return value should be zero
- * or a negative error number; it will be passed to kthread_stop().
- *
- * Returns a task_struct or ERR_PTR(-ENOMEM).
- */
-struct task_struct *kthread_create(int (*threadfn)(void *data),
-				   void *data,
-				   const char namefmt[],
-				   ...)
+struct task_struct *__kthread_create(int (*threadfn)(void *data),
+				     void *data,
+				     const char namefmt[],
+				     ...)
 {
 	struct kthread_create_info create;
 
@@ -149,7 +130,7 @@ struct task_struct *kthread_create(int (
 	}
 	return create.result;
 }
-EXPORT_SYMBOL(kthread_create);
+EXPORT_SYMBOL(__kthread_create);
 
 /**
  * kthread_bind - bind a just-created kthread to a cpu.