Add an API for easily creating userspace threads in kernelspace.

This change refactors the existing create_thread() function to be more
generic. It replaces almost all of its arguments by a callback that can
be used to extract the thread ID and copy it out to the right place, but
also to perform additional initialization steps, such as setting the
trapframe. This also makes the difference between thr_new() and
thr_create() more clear in my opinion.

This function is going to be used by the CloudABI compatibility layer.

It looks like the OpenSolaris compatibility framework already provides a
function called thread_create(). Rename this function to
do_thread_create() and use a macro to deal with the namespacing
conflict. A similar approach is already used for thread_exit().

MFC after:	1 month

sys/cddl/compat/opensolaris/sys/proc.h

@@ -63,7 +63,7 @@ typedef struct proc	proc_t;
 extern struct proc *zfsproc;
 
 static __inline kthread_t *
-thread_create(caddr_t stk, size_t stksize, void (*proc)(void *), void *arg,
+do_thread_create(caddr_t stk, size_t stksize, void (*proc)(void *), void *arg,
     size_t len, proc_t *pp, int state, pri_t pri)
 {
 	kthread_t *td = NULL;
@@ -88,6 +88,8 @@ thread_create(caddr_t stk, size_t stksize, void (*proc)(void *), void *arg,
 	return (td);
 }
 
+#define	thread_create(stk, stksize, proc, arg, len, pp, state, pri) \
+	do_thread_create(stk, stksize, proc, arg, len, pp, state, pri)
 #define	thread_exit()	kthread_exit()
 
 #endif	/* _KERNEL */

sys/kern/kern_thr.c

@@ -89,29 +89,39 @@ suword_lwpid(void *addr, lwpid_t lwpid)
 #define suword_lwpid	suword
 #endif
 
-static int create_thread(struct thread *td, mcontext_t *ctx,
-			 void (*start_func)(void *), void *arg,
-			 char *stack_base, size_t stack_size,
-			 char *tls_base,
-			 long *child_tid, long *parent_tid,
-			 int flags, struct rtprio *rtp);
-
 /*
  * System call interface.
  */
+
+struct thr_create_initthr_args {
+	ucontext_t ctx;
+	long *tid;
+};
+
+static int
+thr_create_initthr(struct thread *td, void *thunk)
+{
+	struct thr_create_initthr_args *args;
+
+	/* Copy out the child tid. */
+	args = thunk;
+	if (args->tid != NULL && suword_lwpid(args->tid, td->td_tid))
+		return (EFAULT);
+
+	return (set_mcontext(td, &args->ctx.uc_mcontext));
+}
+
 int
 sys_thr_create(struct thread *td, struct thr_create_args *uap)
     /* ucontext_t *ctx, long *id, int flags */
 {
-	ucontext_t ctx;
+	struct thr_create_initthr_args args;
 	int error;
 
-	if ((error = copyin(uap->ctx, &ctx, sizeof(ctx))))
+	if ((error = copyin(uap->ctx, &args.ctx, sizeof(args.ctx))))
 		return (error);
-
-	error = create_thread(td, &ctx.uc_mcontext, NULL, NULL,
-		NULL, 0, NULL, uap->id, NULL, uap->flags, NULL);
-	return (error);
+	args.tid = uap->id;
+	return (thread_create(td, NULL, thr_create_initthr, &args));
 }
 
 int
@@ -129,6 +139,35 @@ sys_thr_new(struct thread *td, struct thr_new_args *uap)
 	return (kern_thr_new(td, &param));
 }
 
+static int
+thr_new_initthr(struct thread *td, void *thunk)
+{
+	stack_t stack;
+	struct thr_param *param;
+
+	/*
+	 * Here we copy out tid to two places, one for child and one
+	 * for parent, because pthread can create a detached thread,
+	 * if parent wants to safely access child tid, it has to provide
+	 * its storage, because child thread may exit quickly and
+	 * memory is freed before parent thread can access it.
+	 */
+	param = thunk;
+	if ((param->child_tid != NULL &&
+	    suword_lwpid(param->child_tid, td->td_tid)) ||
+	    (param->parent_tid != NULL &&
+	    suword_lwpid(param->parent_tid, td->td_tid)))
+		return (EFAULT);
+
+	/* Set up our machine context. */
+	stack.ss_sp = param->stack_base;
+	stack.ss_size = param->stack_size;
+	/* Set upcall address to user thread entry function. */
+	cpu_set_upcall_kse(td, param->start_func, param->arg, &stack);
+	/* Setup user TLS address and TLS pointer register. */
+	return (cpu_set_user_tls(td, param->tls_base));
+}
+
 int
 kern_thr_new(struct thread *td, struct thr_param *param)
 {
@@ -142,22 +181,13 @@ kern_thr_new(struct thread *td, struct thr_param *param)
 			return (error);
 		rtpp = &rtp;
 	}
-	error = create_thread(td, NULL, param->start_func, param->arg,
-		param->stack_base, param->stack_size, param->tls_base,
-		param->child_tid, param->parent_tid, param->flags,
-		rtpp);
-	return (error);
+	return (thread_create(td, rtpp, thr_new_initthr, param));
 }
 
-static int
-create_thread(struct thread *td, mcontext_t *ctx,
-	    void (*start_func)(void *), void *arg,
-	    char *stack_base, size_t stack_size,
-	    char *tls_base,
-	    long *child_tid, long *parent_tid,
-	    int flags, struct rtprio *rtp)
+int
+thread_create(struct thread *td, struct rtprio *rtp,
+    int (*initialize_thread)(struct thread *, void *), void *thunk)
 {
-	stack_t stack;
 	struct thread *newtd;
 	struct proc *p;
 	int error;
@@ -199,24 +229,6 @@ create_thread(struct thread *td, mcontext_t *ctx,
 
 	cpu_set_upcall(newtd, td);
 
-	/*
-	 * Try the copyout as soon as we allocate the td so we don't
-	 * have to tear things down in a failure case below.
-	 * Here we copy out tid to two places, one for child and one
-	 * for parent, because pthread can create a detached thread,
-	 * if parent wants to safely access child tid, it has to provide 
-	 * its storage, because child thread may exit quickly and
-	 * memory is freed before parent thread can access it.
-	 */
-	if ((child_tid != NULL &&
-	    suword_lwpid(child_tid, newtd->td_tid)) ||
-	    (parent_tid != NULL &&
-	    suword_lwpid(parent_tid, newtd->td_tid))) {
-		thread_free(newtd);
-		error = EFAULT;
-		goto fail;
-	}
-
 	bzero(&newtd->td_startzero,
 	    __rangeof(struct thread, td_startzero, td_endzero));
 	bcopy(&td->td_startcopy, &newtd->td_startcopy,
@@ -224,26 +236,11 @@ create_thread(struct thread *td, mcontext_t *ctx,
 	newtd->td_proc = td->td_proc;
 	thread_cow_get(newtd, td);
 
-	if (ctx != NULL) { /* old way to set user context */
-		error = set_mcontext(newtd, ctx);
-		if (error != 0) {
-			thread_cow_free(newtd);
-			thread_free(newtd);
-			goto fail;
-		}
-	} else {
-		/* Set up our machine context. */
-		stack.ss_sp = stack_base;
-		stack.ss_size = stack_size;
-		/* Set upcall address to user thread entry function. */
-		cpu_set_upcall_kse(newtd, start_func, arg, &stack);
-		/* Setup user TLS address and TLS pointer register. */
-		error = cpu_set_user_tls(newtd, tls_base);
-		if (error != 0) {
-			thread_cow_free(newtd);
-			thread_free(newtd);
-			goto fail;
-		}
+	error = initialize_thread(newtd, thunk);
+	if (error != 0) {
+		thread_cow_free(newtd);
+		thread_free(newtd);
+		goto fail;
 	}
 
 	PROC_LOCK(p);

sys/sys/proc.h

@@ -992,6 +992,8 @@ void	thread_cow_get_proc(struct thread *newtd, struct proc *p);
 void	thread_cow_get(struct thread *newtd, struct thread *td);
 void	thread_cow_free(struct thread *td);
 void	thread_cow_update(struct thread *td);
+int	thread_create(struct thread *td, struct rtprio *rtp,
+	    int (*initialize_thread)(struct thread *, void *), void *thunk);
 void	thread_exit(void) __dead2;
 void	thread_free(struct thread *td);
 void	thread_link(struct thread *td, struct proc *p);