kthread abstraction, take two

This is a new version of the ktread abstraction which incorporates suggestions by Andi Kleen, Jeff Garzik and Andrew Morton.

The changes are:

- kthread_start now takes a void * for the user-data, so it doesn't have to be part of struct kthread.
- the main method of struct kthread now returns an integers, if it is negative, the thread will be stopped.
- kthread_main no more does the scheduling, it has to be done by the mainloop now.

The API is now:

int kthread_start(struct kthread *kth, void *data)

Startup a new kernel thread as described by 'kth' (details below). Wait until it has finished initialization.

void kthread_stop(struct kthread *kth)

Stop the kernel thread described by 'kth'. Wait until is has finished.

int kthread_running(struct kthread *kth)

Return 1 if the kernel thread described by 'kth' is running.

The 'kthread' structure contains all information for this thread. Two fields _must_ be initialized:

const char *name;

Name of the thread.

int (*main)(struct kthread *, void);

Mainloop of the thread. This loop is repeated until the thread is stopped. Stopping is done by either kthread_stop or a negative return value of this method. This routine has to release the timeslice after finishing! (i.e. call schedule() or yield()).

Others may be filled out if needed:

int (*init)(struct kthread *, void *);

Initialize thread before the mainloop is called.

void (*cleanup)(struct kthread *, void *);

Cleanup after the mainloop is done.

void *data;

Opaque data for the thread's use

Patch for 2.5.4-pre5 is below.

Christoph

--

diff -uNr -Xdontdiff ../master/linux-2.5.4-pre5/include/linux/kthread.h linux/include/linux/kthread.h
@@ -0,0 +1,22 @@
+#ifndef _LINUX_KTHREAD_H
+#define _LINUX_KTHREAD_H
+
+struct task_struct;
+
+struct kthread {
+	const char *name;
+	struct task_struct *task;
+	struct completion done;
+#define KTH_RUNNING	1
+#define KTH_SHUTDOWN	2
+	long state;
+	int (*init)(struct kthread *, void *);
+	void (*cleanup)(struct kthread *, void *);
+	int (*main)(struct kthread *, void *);
+};
+
+extern int kthread_start(struct kthread *, void *);
+extern void kthread_stop(struct kthread *);
+extern int kthread_running(struct kthread *);
+
+#endif /* _LINUX_KTHREAD_H */

diff -uNr -Xdontdiff ../master/linux-2.5.4-pre5/kernel/Makefile linux/kernel/Makefile
@@ -10,12 +10,12 @@
 O_TARGET := kernel.o
 
 export-objs = signal.o sys.o kmod.o context.o ksyms.o pm.o exec_domain.o \
-		printk.o 
+		printk.o kthread.o
 
 obj-y     = sched.o dma.o fork.o exec_domain.o panic.o printk.o \
 	    module.o exit.o itimer.o info.o time.o softirq.o resource.o \
 	    sysctl.o acct.o capability.o ptrace.o timer.o user.o \
-	    signal.o sys.o kmod.o context.o 
+	    signal.o sys.o kmod.o context.o kthread.o
 
 obj-$(CONFIG_UID16) += uid16.o
 obj-$(CONFIG_MODULES) += ksyms.o

Nice. I like it.

Would you consider converting a few places in the kernel to use kthread, just as an example to show people what a sample implementation would look like?

Jeff

Jeff Garzik      | "I went through my candy like hot oatmeal
Building 1024    |  through an internally-buttered weasel."
MandrakeSoft     |             - goats.com

Hi!

Could you convert some kernel thread to the new interface to show how it simplifies things?
Pavel

(about SSSCA) "I don't say this lightly.  However, I really think that the U.S.
no longer is classifiable as a democracy, but rather as a plutocracy." --hpa