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