IO 上下文 io_context

此结构用于跟踪进程的IO处理，此结构可在多个进程之间共享。

/*
 * I/O subsystem state of the associated processes.  It is refcounted
 * and kmalloc'ed. These could be shared between processes.
 */
struct io_context {
	atomic_long_t refcount;
	atomic_t active_ref;
	atomic_t nr_tasks;

	/* all the fields below are protected by this lock */
	spinlock_t lock;
	unsigned short ioprio;
	/*
	 * For request batching
	 */
	int nr_batch_requests;     /* Number of requests left in the batch */
	unsigned long last_waited; /* Time last woken after wait for request */
	struct radix_tree_root	icq_tree;
	struct io_cq __rcu	*icq_hint;
	struct hlist_head	icq_list;
	struct work_struct release_work;
};

函数create_task_io_context()用于创建io_context

int create_task_io_context(struct task_struct *task, gfp_t gfp_flags, int node)
{
	struct io_context *ioc;
	int ret;

	ioc = kmem_cache_alloc_node(iocontext_cachep, gfp_flags |
 
			
	if (unlikely(!ioc))
		return -ENOMEM;


	/* initialize */
	atomic_long_set(&ioc->refcount, 1);
	atomic_set(&ioc->nr_tasks, 1);
	atomic_set(&ioc->active_ref, 1);
	spin_lock_init(&ioc->lock);
	INIT_RADIX_TREE(&ioc->icq_tree, GFP_ATOMIC | __GFP_HIGH);
	INIT_HLIST_HEAD(&ioc->icq_list);
	INIT_WORK(&ioc->release_work, ioc_release_fn);


	/*
	 * Try to install.  ioc shouldn't be installed if someone else
	 * already did or @task, which isn't %current, is exiting.  Note
	 * that we need to allow ioc creation on exiting %current as exit
	 * path may issue IOs from e.g. exit_files().  The exit path is
	 * responsible for not issuing IO after exit_io_context().
	 */
	task_lock(task);
	if (!task->io_context && (task == current || !(task->flags & PF_EXITING)))
		task->io_context = ioc;
	else
		kmem_cache_free(iocontext_cachep, ioc);


	ret = task->io_context ? 0 : -EBUSY;


	task_unlock(task);


	return ret;
}
 
 
static struct kmem_cache *iocontext_cachep;
 
create_task_io_context()

 
void ioc_release_fn(struct work_struct *work)
 
int __init blk_ioc_init(void)
{
	iocontext_cachep = kmem_cache_create("blkdev_ioc",
			sizeof(struct io_context), 0, SLAB_PANIC, NULL);
	return 0;
}
subsys_initcall(blk_ioc_init);
 

 

 
get_task_io_context

 
	create_task_io_context
 

 
set_task_ioprio:ioprio_set, ext4_fill_super, ext4_remount

 
copy_io:fork