inode节点clear操作

inode 节点clear是把节点设置处于一种状态，即

I_FREEING | I_CLEAR

* I_FREEING		Set when inode is about to be freed but still has dirty
 *			pages or buffers attached or the inode itself is still
 *			dirty.
 * I_CLEAR		Added by clear_inode().  In this state the inode is
 *			clean and can be destroyed.  Inode keeps I_FREEING.

void clear_inode(struct inode *inode)
{
	might_sleep();
	/*
	 * We have to cycle tree_lock here because reclaim can be still in the
	 * process of removing the last page (in __delete_from_page_cache())
	 * and we must not free mapping under it.
	 */
	spin_lock_irq(&inode->i_data.tree_lock);
	BUG_ON(inode->i_data.nrpages);
	BUG_ON(inode->i_data.nrexceptional);
	spin_unlock_irq(&inode->i_data.tree_lock);
	BUG_ON(!list_empty(&inode->i_data.private_list));
	BUG_ON(!(inode->i_state & I_FREEING));
	BUG_ON(inode->i_state & I_CLEAR);
	BUG_ON(!list_empty(&inode->i_wb_list));
	/* don't need i_lock here, no concurrent mods to i_state */
	inode->i_state = I_FREEING | I_CLEAR;
}
EXPORT_SYMBOL(clear_inode);