[patch 07/12] syslets: x86, add create_async_thread() method

[Ingo Molnar <mingo@elte.hu>]

From: Ingo Molnar <mingo@elte.hu>

add the create_async_thread() way of creating kernel threads:
these threads first execute a kernel function and when they
return from it they execute user-space.

An architecture must implement this interface before it can turn
CONFIG_ASYNC_SUPPORT on.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
---
 arch/i386/kernel/entry.S     |   25 +++++++++++++++++++++++++
 arch/i386/kernel/process.c   |   31 +++++++++++++++++++++++++++++++
 include/asm-i386/processor.h |   17 +++++++++++++++++
 include/asm-i386/unistd.h    |   10 ++++++++++
 4 files changed, 83 insertions(+)

Index: linux/arch/i386/kernel/entry.S
===================================================================
--- linux.orig/arch/i386/kernel/entry.S
+++ linux/arch/i386/kernel/entry.S
@@ -1034,6 +1034,31 @@ ENTRY(kernel_thread_helper)
 	CFI_ENDPROC
 ENDPROC(kernel_thread_helper)
 
+ENTRY(async_thread_helper)
+	CFI_STARTPROC
+	/*
+	 * Allocate space on the stack for pt-regs.
+	 * sizeof(struct pt_regs) == 64, and we've got 8 bytes on the
+	 * kernel stack already:
+	 */
+	subl $64-8, %esp
+	CFI_ADJUST_CFA_OFFSET 64-8
+	movl %edx,%eax
+	push %edx
+	CFI_ADJUST_CFA_OFFSET 4
+	call *%ebx
+	addl $4, %esp
+	CFI_ADJUST_CFA_OFFSET -4
+
+	movl %eax, PT_EAX(%esp)
+
+	GET_THREAD_INFO(%ebp)
+
+	jmp syscall_exit
+	CFI_ENDPROC
+ENDPROC(async_thread_helper)
+
+
 .section .rodata,"a"
 #include "syscall_table.S"
 
Index: linux/arch/i386/kernel/process.c
===================================================================
--- linux.orig/arch/i386/kernel/process.c
+++ linux/arch/i386/kernel/process.c
@@ -355,6 +355,37 @@ int kernel_thread(int (*fn)(void *), voi
 EXPORT_SYMBOL(kernel_thread);
 
 /*
+ * This gets run with %ebx containing the
+ * function to call, and %edx containing
+ * the "args".
+ */
+extern void async_thread_helper(void);
+
+/*
+ * Create an async thread
+ */
+int create_async_thread(long (*fn)(void *), void * arg, unsigned long flags)
+{
+	struct pt_regs regs;
+
+	memset(&regs, 0, sizeof(regs));
+
+	regs.ebx = (unsigned long) fn;
+	regs.edx = (unsigned long) arg;
+
+	regs.xds = __USER_DS;
+	regs.xes = __USER_DS;
+	regs.xfs = __KERNEL_PDA;
+	regs.orig_eax = -1;
+	regs.eip = (unsigned long) async_thread_helper;
+	regs.xcs = __KERNEL_CS | get_kernel_rpl();
+	regs.eflags = X86_EFLAGS_IF | X86_EFLAGS_SF | X86_EFLAGS_PF | 0x2;
+
+	/* Ok, create the new task.. */
+	return do_fork(flags, 0, &regs, 0, NULL, NULL);
+}
+
+/*
  * Free current thread data structures etc..
  */
 void exit_thread(void)
Index: linux/include/asm-i386/processor.h
===================================================================
--- linux.orig/include/asm-i386/processor.h
+++ linux/include/asm-i386/processor.h
@@ -472,6 +472,11 @@ extern void prepare_to_copy(struct task_
  */
 extern int kernel_thread(int (*fn)(void *), void * arg, unsigned long flags);
 
+/*
+ * create an async thread:
+ */
+extern int create_async_thread(long (*fn)(void *), void * arg, unsigned long flags);
+
 extern unsigned long thread_saved_pc(struct task_struct *tsk);
 void show_trace(struct task_struct *task, struct pt_regs *regs, unsigned long *stack);
 
@@ -504,6 +509,18 @@ unsigned long get_wchan(struct task_stru
 #define KSTK_EIP(task) (task_pt_regs(task)->eip)
 #define KSTK_ESP(task) (task_pt_regs(task)->esp)
 
+/*
+ * Register access methods for async syscall support.
+ *
+ * Note, task_stack_reg() must not be an lvalue, hence this macro:
+ */
+#define task_stack_reg(t)			\
+		({ unsigned long __esp = task_pt_regs(t)->esp; __esp; })
+#define set_task_stack_reg(t, new_stack)	\
+		do { task_pt_regs(t)->esp = (new_stack); } while (0)
+#define task_ip_reg(t)				task_pt_regs(t)->eip
+#define task_ret_reg(t)				task_pt_regs(t)->eax
+
 
 struct microcode_header {
 	unsigned int hdrver;
Index: linux/include/asm-i386/unistd.h
===================================================================
--- linux.orig/include/asm-i386/unistd.h
+++ linux/include/asm-i386/unistd.h
@@ -1,6 +1,8 @@
 #ifndef _ASM_I386_UNISTD_H_
 #define _ASM_I386_UNISTD_H_
 
+#include <linux/linkage.h>
+
 /*
  * This file contains the system call numbers.
  */
@@ -330,6 +332,14 @@
 
 #define NR_syscalls 320
 
+#ifndef __ASSEMBLY__
+
+typedef asmlinkage long (*syscall_fn_t)(long, long, long, long, long, long);
+
+extern syscall_fn_t sys_call_table[NR_syscalls];
+
+#endif
+
 #define __ARCH_WANT_IPC_PARSE_VERSION
 #define __ARCH_WANT_OLD_READDIR
 #define __ARCH_WANT_OLD_STAT