聊聊块设备那点事

// inode 结构，省略一些字段
struct inode {
	umode_t			i_mode;
	
	const struct inode_operations	*i_op;
	struct super_block	*i_sb;
	unsigned long		i_ino;

	dev_t			i_rdev;
	loff_t			i_size;

	union {
		const struct file_operations	*i_fop;	
		void (*free_inode)(struct inode *);
	};

	union {
		struct pipe_inode_info	*i_pipe;
		struct block_device	*i_bdev;
		struct cdev		*i_cdev;
		char			*i_link;
		unsigned		i_dir_seq;
	};

} __randomize_layout;


// 字符设备、块设备特殊设备的inode初始化函数
void init_special_inode(struct inode *inode, umode_t mode, dev_t rdev)
{
	inode->i_mode = mode;
	if (S_ISCHR(mode)) {
		inode->i_fop = &def_chr_fops;
		inode->i_rdev = rdev;
	} else if (S_ISBLK(mode)) {
		inode->i_fop = &def_blk_fops;
		inode->i_rdev = rdev;
	} else if (S_ISFIFO(mode))
		inode->i_fop = &pipefifo_fops;
	else if (S_ISSOCK(mode))
		;	/* leave it no_open_fops */
	else
		printk(KERN_DEBUG "init_special_inode: bogus i_mode (%o) for"
				  " inode %s:%lu\n", mode, inode->i_sb->s_id,
				  inode->i_ino);
}
EXPORT_SYMBOL(init_special_inode);

struct block_device {
	// bd_dev保存块设备号
	dev_t			bd_dev;
	// bd_openers表示块设备打开的次数
	int			bd_openers;
	// bd_inode指向bdev伪文件系统的inode，未来会废弃
	struct inode *		bd_inode;	/* will die */
	
	struct super_block *	bd_super;
	struct mutex		bd_mutex;	/* open/close mutex */
	void *			bd_claiming;
	void *			bd_holder;
	int			bd_holders;
	bool			bd_write_holder;
#ifdef CONFIG_SYSFS
	struct list_head	bd_holder_disks;
#endif
	struct block_device *	bd_contains;
	u8			bd_partno;
	// db_part用来表示块设备上的分区
	struct hd_struct *	bd_part;
	/* number of times partitions within this device have been opened. */
	unsigned		bd_part_count;

	spinlock_t		bd_size_lock; /* for bd_inode->i_size updates */
	// bd_disk已经分区的磁盘的抽象层
	struct gendisk *	bd_disk;
	struct backing_dev_info *bd_bdi;

	/* The counter of freeze processes */
	int			bd_fsfreeze_count;
	/* Mutex for freeze */
	struct mutex		bd_fsfreeze_mutex;
} __randomize_layout;

// cfq调度算法
static struct elevator_type iosched_cfq = {
	.ops.sq = {
		// 检查下一新的请求是否与可以和现在的请求合并
		.elevator_merge_fn = 		cfq_merge,
		// 请求合并后调用
		.elevator_merged_fn =		cfq_merged_request,
		// 将两个请求合并为一个请求
		.elevator_merge_req_fn =	cfq_merged_requests,
		.elevator_allow_bio_merge_fn =	cfq_allow_bio_merge,
		.elevator_allow_rq_merge_fn =	cfq_allow_rq_merge,
		.elevator_bio_merged_fn =	cfq_bio_merged,
		// 从给定的队列中选择下一步应该调度执行的请求
		.elevator_dispatch_fn =		cfq_dispatch_requests,
		// 添加请求到队列
		.elevator_add_req_fn =		cfq_insert_request,
		.elevator_activate_req_fn =	cfq_activate_request,
		.elevator_deactivate_req_fn =	cfq_deactivate_request,
		.elevator_completed_req_fn =	cfq_completed_request,
		.elevator_former_req_fn =	elv_rb_former_request,
		.elevator_latter_req_fn =	elv_rb_latter_request,
		.elevator_init_icq_fn =		cfq_init_icq,
		.elevator_exit_icq_fn =		cfq_exit_icq,
		// 创建新请求时调用
		.elevator_set_req_fn =		cfq_set_request,
		// 释放回内存子系统时调用
		.elevator_put_req_fn =		cfq_put_request,
		.elevator_may_queue_fn =	cfq_may_queue,
		// 请求队列初始化时候调用
		.elevator_init_fn =		cfq_init_queue,
		// 请求队列释放时候调用
		.elevator_exit_fn =		cfq_exit_queue,
		.elevator_registered_fn =	cfq_registered_queue,
	},
	.icq_size	=	sizeof(struct cfq_io_cq),
	.icq_align	=	__alignof__(struct cfq_io_cq),
	.elevator_attrs =	cfq_attrs,
	.elevator_name	=	"cfq",
	.elevator_owner =	THIS_MODULE,
};

// deadline调度算法
static struct elevator_type iosched_deadline = {
	.ops.sq = {
		.elevator_merge_fn = 		deadline_merge,
		.elevator_merged_fn =		deadline_merged_request,
		.elevator_merge_req_fn =	deadline_merged_requests,
		.elevator_dispatch_fn =		deadline_dispatch_requests,
		.elevator_completed_req_fn =	deadline_completed_request,
		.elevator_add_req_fn =		deadline_add_request,
		.elevator_former_req_fn =	elv_rb_former_request,
		.elevator_latter_req_fn =	elv_rb_latter_request,
		.elevator_init_fn =		deadline_init_queue,
		.elevator_exit_fn =		deadline_exit_queue,
	},

	.elevator_attrs = deadline_attrs,
	.elevator_name = "deadline",
	.elevator_owner = THIS_MODULE,
};

//  noop 调度算法
static struct elevator_type elevator_noop = {
	.ops.sq = {
		.elevator_merge_req_fn		= noop_merged_requests,
		.elevator_dispatch_fn		= noop_dispatch,
		.elevator_add_req_fn		= noop_add_request,
		.elevator_former_req_fn		= noop_former_request,
		.elevator_latter_req_fn		= noop_latter_request,
		.elevator_init_fn		= noop_init_queue,
		.elevator_exit_fn		= noop_exit_queue,
	},
	.elevator_name = "noop",
	.elevator_owner = THIS_MODULE,
};