[patch 07/13] syslets: x86, add create_async_thread() method

Ingo Molnar
2007-02-21T21:21:08Z

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 | 5 +++++
3 files changed, 61 insertions(+)

Index: linux/arch/i386/kernel/entry.S
===================================================================
--- linux.orig/arch/i386/kernel/entry.S
+++ linux/arch/i386/kernel/entry.S
@@ -996,6 +996,31 @@ 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
+ 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
@@ -352,6 +352,37 @@ 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(int (*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.xgs = __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(int (*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);