【Linux 内核】进程管理 ( 进程相关系统调用源码分析 | fork() 源码 | vfork() 源码 | clone() 源码 | _do_fork() 源码 | do_fork() 源码 )

韩曙亮

发布于 2023-03-30 13:48:14

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发布于 2023-03-30 13:48:14

文章被收录于专栏：韩曙亮的移动开发专栏

文章目录

Linux 进程相关 " 系统调用 " 对应的源码在 linux-5.6.18\kernel\fork.c 源码中 , 下面开始对该源码的相关 " 系统调用 " 进行分析 ;

一、fork 系统调用源码

fork() 系统调用函数 , 最终返回的是 _do_fork() 函数执行结果 ;

#ifdef __ARCH_WANT_SYS_FORK
SYSCALL_DEFINE0(fork)
{
#ifdef CONFIG_MMU
	struct kernel_clone_args args = {
		.exit_signal = SIGCHLD,
	};

	return _do_fork(&args);
#else
	/* can not support in nommu mode */
	return -EINVAL;
#endif
}
#endif

二、vfork 系统调用源码

vfork() 系统调用函数 , 最终返回的是 _do_fork() 函数执行结果 ;

#ifdef __ARCH_WANT_SYS_VFORK
SYSCALL_DEFINE0(vfork)
{
	struct kernel_clone_args args = {
		.flags		= CLONE_VFORK | CLONE_VM,
		.exit_signal	= SIGCHLD,
	};

	return _do_fork(&args);
}
#endif

三、clone 系统调用源码

clone() 系统调用函数 , 最终返回的是 _do_fork() 函数执行结果 ;

#ifdef __ARCH_WANT_SYS_CLONE
#ifdef CONFIG_CLONE_BACKWARDS
SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
		 int __user *, parent_tidptr,
		 unsigned long, tls,
		 int __user *, child_tidptr)
#elif defined(CONFIG_CLONE_BACKWARDS2)
SYSCALL_DEFINE5(clone, unsigned long, newsp, unsigned long, clone_flags,
		 int __user *, parent_tidptr,
		 int __user *, child_tidptr,
		 unsigned long, tls)
#elif defined(CONFIG_CLONE_BACKWARDS3)
SYSCALL_DEFINE6(clone, unsigned long, clone_flags, unsigned long, newsp,
		int, stack_size,
		int __user *, parent_tidptr,
		int __user *, child_tidptr,
		unsigned long, tls)
#else
SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
		 int __user *, parent_tidptr,
		 int __user *, child_tidptr,
		 unsigned long, tls)
#endif
{
	struct kernel_clone_args args = {
		.flags		= (lower_32_bits(clone_flags) & ~CSIGNAL),
		.pidfd		= parent_tidptr,
		.child_tid	= child_tidptr,
		.parent_tid	= parent_tidptr,
		.exit_signal	= (lower_32_bits(clone_flags) & CSIGNAL),
		.stack		= newsp,
		.tls		= tls,
	};

	if (!legacy_clone_args_valid(&args))
		return -EINVAL;

	return _do_fork(&args);
}
#endif

四、_do_fork 函数源码

在 _do_fork() 函数中 , 调用了 copy_process() 函数 ;

/*
 *  Ok, this is the main fork-routine.
 *
 * It copies the process, and if successful kick-starts
 * it and waits for it to finish using the VM if required.
 *
 * args->exit_signal is expected to be checked for sanity by the caller.
 */
long _do_fork(struct kernel_clone_args *args)
{
	u64 clone_flags = args->flags;
	struct completion vfork;
	struct pid *pid;
	struct task_struct *p;
	int trace = 0;
	long nr;

	/*
	 * Determine whether and which event to report to ptracer.  When
	 * called from kernel_thread or CLONE_UNTRACED is explicitly
	 * requested, no event is reported; otherwise, report if the event
	 * for the type of forking is enabled.
	 */
	if (!(clone_flags & CLONE_UNTRACED)) {
		if (clone_flags & CLONE_VFORK)
			trace = PTRACE_EVENT_VFORK;
		else if (args->exit_signal != SIGCHLD)
			trace = PTRACE_EVENT_CLONE;
		else
			trace = PTRACE_EVENT_FORK;

		if (likely(!ptrace_event_enabled(current, trace)))
			trace = 0;
	}

	p = copy_process(NULL, trace, NUMA_NO_NODE, args);
	add_latent_entropy();

	// ...
	return nr;
}

五、do_fork 函数源码

do_fork() 函数有

个参数 ,

unsigned long clone_flags 参数表示创建进程的标志位集合 ;

unsigned long stack_start 参数表示用户空间栈起始地址 ;

unsigned long stack_size 参数表示用户空间栈大小 , 通常为

;

int __user *parent_tidptr 参数表示指向用户空间地址的指针 , 该指针指向父进程的进程号 ;

int __user *child_tidptr 参数表示指向用户空间地址的指针 , 该指针指向子进程的进程号 ;

#ifndef CONFIG_HAVE_COPY_THREAD_TLS
/* For compatibility with architectures that call do_fork directly rather than
 * using the syscall entry points below. */
long do_fork(unsigned long clone_flags,
	      unsigned long stack_start,
	      unsigned long stack_size,
	      int __user *parent_tidptr,
	      int __user *child_tidptr)
{
	struct kernel_clone_args args = {
		.flags		= (lower_32_bits(clone_flags) & ~CSIGNAL),
		.pidfd		= parent_tidptr,
		.child_tid	= child_tidptr,
		.parent_tid	= parent_tidptr,
		.exit_signal	= (lower_32_bits(clone_flags) & CSIGNAL),
		.stack		= stack_start,
		.stack_size	= stack_size,
	};

	if (!legacy_clone_args_valid(&args))
		return -EINVAL;

	return _do_fork(&args);
}
#endif