自学教程：C++ task_io_accounting_init函数代码示例

//.........这里部分代码省略.........	/*	 * If multiple threads are within copy_process(), then this check	 * triggers too late. This doesn't hurt, the check is only there	 * to stop root fork bombs.	 */	retval = -EAGAIN;	if (nr_threads >= max_threads)		goto bad_fork_cleanup_count;	if (!try_module_get(task_thread_info(p)->exec_domain->module))		goto bad_fork_cleanup_count;	p->did_exec = 0;	delayacct_tsk_init(p);	/* Must remain after dup_task_struct() */	copy_flags(clone_flags, p);	INIT_LIST_HEAD(&p->children);	INIT_LIST_HEAD(&p->sibling);	rcu_copy_process(p);	p->vfork_done = NULL;	spin_lock_init(&p->alloc_lock);	init_sigpending(&p->pending);	p->utime = cputime_zero;	p->stime = cputime_zero;	p->gtime = cputime_zero;	p->utimescaled = cputime_zero;	p->stimescaled = cputime_zero;	p->prev_utime = cputime_zero;	p->prev_stime = cputime_zero;	p->default_timer_slack_ns = current->timer_slack_ns;	task_io_accounting_init(&p->ioac);	acct_clear_integrals(p);	posix_cpu_timers_init(p);	p->lock_depth = -1;		/* -1 = no lock */	do_posix_clock_monotonic_gettime(&p->start_time);	p->real_start_time = p->start_time;	monotonic_to_bootbased(&p->real_start_time);	p->io_context = NULL;	p->audit_context = NULL;	cgroup_fork(p);#ifdef CONFIG_NUMA	p->mempolicy = mpol_dup(p->mempolicy); 	if (IS_ERR(p->mempolicy)) { 		retval = PTR_ERR(p->mempolicy); 		p->mempolicy = NULL; 		goto bad_fork_cleanup_cgroup; 	}	mpol_fix_fork_child_flag(p);#endif#ifdef CONFIG_TRACE_IRQFLAGS	p->irq_events = 0;#ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW	p->hardirqs_enabled = 1;#else	p->hardirqs_enabled = 0;#endif	p->hardirq_enable_ip = 0;	p->hardirq_enable_event = 0;	p->hardirq_disable_ip = _THIS_IP_;	p->hardirq_disable_event = 0;	p->softirqs_enabled = 1;

//.........这里部分代码省略.........	 */	retval = -EAGAIN;	if (nr_threads >= max_threads)		goto bad_fork_cleanup_count;	delayacct_tsk_init(p);	/* Must remain after dup_task_struct() */	p->flags &= ~(PF_SUPERPRIV | PF_WQ_WORKER);	p->flags |= PF_FORKNOEXEC;	INIT_LIST_HEAD(&p->children);	INIT_LIST_HEAD(&p->sibling);	rcu_copy_process(p);	p->vfork_done = NULL;	spin_lock_init(&p->alloc_lock);	init_sigpending(&p->pending);	p->utime = p->stime = p->gtime = 0;	p->utimescaled = p->stimescaled = 0;#ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE	p->prev_cputime.utime = p->prev_cputime.stime = 0;#endif#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN	seqlock_init(&p->vtime_seqlock);	p->vtime_snap = 0;	p->vtime_snap_whence = VTIME_SLEEPING;#endif#if defined(SPLIT_RSS_COUNTING)	memset(&p->rss_stat, 0, sizeof(p->rss_stat));#endif	p->default_timer_slack_ns = current->timer_slack_ns;	task_io_accounting_init(&p->ioac);	acct_clear_integrals(p);	posix_cpu_timers_init(p);	p->start_time = ktime_get_ns();	p->real_start_time = ktime_get_boot_ns();	p->io_context = NULL;	p->audit_context = NULL;	if (clone_flags & CLONE_THREAD)		threadgroup_change_begin(current);	cgroup_fork(p);#ifdef CONFIG_NUMA	p->mempolicy = mpol_dup(p->mempolicy);	if (IS_ERR(p->mempolicy)) {		retval = PTR_ERR(p->mempolicy);		p->mempolicy = NULL;		goto bad_fork_cleanup_threadgroup_lock;	}#endif#ifdef CONFIG_CPUSETS	p->cpuset_mem_spread_rotor = NUMA_NO_NODE;	p->cpuset_slab_spread_rotor = NUMA_NO_NODE;	seqcount_init(&p->mems_allowed_seq);#endif#ifdef CONFIG_TRACE_IRQFLAGS	p->irq_events = 0;	p->hardirqs_enabled = 0;	p->hardirq_enable_ip = 0;	p->hardirq_enable_event = 0;	p->hardirq_disable_ip = _THIS_IP_;	p->hardirq_disable_event = 0;	p->softirqs_enabled = 1;

//.........这里部分代码省略.........		goto bad_fork_cleanup_put_domain;	p->did_exec = 0;	delayacct_tsk_init(p);	/* Must remain after dup_task_struct() */	copy_flags(clone_flags, p);	p->pid = pid_nr(pid);	retval = -EFAULT;	if (clone_flags & CLONE_PARENT_SETTID)		if (put_user(p->pid, parent_tidptr))			goto bad_fork_cleanup_delays_binfmt;	INIT_LIST_HEAD(&p->children);	INIT_LIST_HEAD(&p->sibling);	p->vfork_done = NULL;	spin_lock_init(&p->alloc_lock);	clear_tsk_thread_flag(p, TIF_SIGPENDING);	init_sigpending(&p->pending);	p->utime = cputime_zero;	p->stime = cputime_zero; 	p->sched_time = 0;#ifdef CONFIG_DETECT_SOFTLOCKUP	p->last_switch_count = 0;	p->last_switch_timestamp = 0;#endif#ifdef CONFIG_TASK_XACCT	p->rchar = 0;		/* I/O counter: bytes read */	p->wchar = 0;		/* I/O counter: bytes written */	p->syscr = 0;		/* I/O counter: read syscalls */	p->syscw = 0;		/* I/O counter: write syscalls */#endif	task_io_accounting_init(p);	acct_clear_integrals(p); 	p->it_virt_expires = cputime_zero;	p->it_prof_expires = cputime_zero; 	p->it_sched_expires = 0; 	INIT_LIST_HEAD(&p->cpu_timers[0]); 	INIT_LIST_HEAD(&p->cpu_timers[1]); 	INIT_LIST_HEAD(&p->cpu_timers[2]);	p->lock_depth = -1;		/* -1 = no lock */	do_posix_clock_monotonic_gettime(&p->start_time);#ifdef CONFIG_SECURITY	p->security = NULL;#endif	p->io_context = NULL;	p->audit_context = NULL;	cpuset_fork(p);#ifdef CONFIG_NUMA 	p->mempolicy = mpol_copy(p->mempolicy); 	if (IS_ERR(p->mempolicy)) { 		retval = PTR_ERR(p->mempolicy); 		p->mempolicy = NULL; 		goto bad_fork_cleanup_cpuset; 	}	mpol_fix_fork_child_flag(p);#endif#ifdef CONFIG_TRACE_IRQFLAGS	p->irq_events = 0;#ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW	p->hardirqs_enabled = 1;#else	p->hardirqs_enabled = 0;

static struct task_struct *copy_process(unsigned long clone_flags,					unsigned long stack_start,					struct pt_regs *regs,					unsigned long stack_size,					int __user *child_tidptr,					struct pid *pid,					int trace){	int retval;	struct task_struct *p;	int cgroup_callbacks_done = 0;	if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))		return ERR_PTR(-EINVAL);	if ((clone_flags & CLONE_THREAD) && !(clone_flags & CLONE_SIGHAND))		return ERR_PTR(-EINVAL);	if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM))		return ERR_PTR(-EINVAL);	if ((clone_flags & CLONE_PARENT) &&				current->signal->flags & SIGNAL_UNKILLABLE)		return ERR_PTR(-EINVAL);	retval = security_task_create(clone_flags);	if (retval)		goto fork_out;	retval = -ENOMEM;	p = dup_task_struct(current);	if (!p)		goto fork_out;	ftrace_graph_init_task(p);	rt_mutex_init_task(p);#ifdef CONFIG_PROVE_LOCKING	DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled);	DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);#endif	retval = -EAGAIN;	if (atomic_read(&p->real_cred->user->processes) >=			task_rlimit(p, RLIMIT_NPROC)) {		if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_RESOURCE) &&		    p->real_cred->user != INIT_USER)			goto bad_fork_free;	}	current->flags &= ~PF_NPROC_EXCEEDED;	retval = copy_creds(p, clone_flags);	if (retval < 0)		goto bad_fork_free;	retval = -EAGAIN;	if (nr_threads >= max_threads)		goto bad_fork_cleanup_count;	if (!try_module_get(task_thread_info(p)->exec_domain->module))		goto bad_fork_cleanup_count;	p->did_exec = 0;	delayacct_tsk_init(p);		copy_flags(clone_flags, p);	INIT_LIST_HEAD(&p->children);	INIT_LIST_HEAD(&p->sibling);	rcu_copy_process(p);	p->vfork_done = NULL;	spin_lock_init(&p->alloc_lock);	init_sigpending(&p->pending);	p->utime = p->stime = p->gtime = 0;	p->utimescaled = p->stimescaled = 0;#ifndef CONFIG_VIRT_CPU_ACCOUNTING	p->prev_utime = p->prev_stime = 0;#endif#if defined(SPLIT_RSS_COUNTING)	memset(&p->rss_stat, 0, sizeof(p->rss_stat));#endif	p->default_timer_slack_ns = current->timer_slack_ns;	task_io_accounting_init(&p->ioac);	acct_clear_integrals(p);	posix_cpu_timers_init(p);	do_posix_clock_monotonic_gettime(&p->start_time);	p->real_start_time = p->start_time;	monotonic_to_bootbased(&p->real_start_time);	p->io_context = NULL;	p->audit_context = NULL;	if (clone_flags & CLONE_THREAD)		threadgroup_change_begin(current);	cgroup_fork(p);#ifdef CONFIG_NUMA	p->mempolicy = mpol_dup(p->mempolicy);	if (IS_ERR(p->mempolicy)) {//.........这里部分代码省略.........