参考：【块设备】通用块层 struct bio 详解 | zzm (aliez22.github.io)

一、Linux 中块设备驱动框架

二、块设备基本概念

1、扇区的概念来自硬件，扇区是硬件最小操作单位。

2、块的概念来自文件系统，是文件系统数据处理的最小单位。

3、段的概念来自操作系统，是内核对内存管理机制的最小单位。

4、页的概念来自操作系统，是内核内存映射管理的最小单位。

三、磁盘分区相关概念

硬盘分区的相关概念（主分区，扩展分区，逻辑分区，MBR，DBR） - 假程序猿 - 博客园 (cnblogs.com)

四、块设备驱动框架中几个重要对象

1、逻辑块设备

struct block_device {dev_t			bd_dev;  /* not a kdev_t - it's a search key */int			bd_openers;struct inode *		bd_inode;	/* will die */struct super_block *	bd_super;struct mutex		bd_mutex;	/* open/close mutex */struct list_head	bd_inodes;void *			bd_claiming;void *			bd_holder;int			bd_holders;bool			bd_write_holder;
#ifdef CONFIG_SYSFSstruct list_head	bd_holder_disks;
#endifstruct block_device *	bd_contains;unsigned		bd_block_size;struct hd_struct *	bd_part;/* number of times partitions within this device have been opened. */unsigned		bd_part_count;int			bd_invalidated;struct gendisk *	bd_disk;struct request_queue *  bd_queue;struct list_head	bd_list;/** Private data.  You must have bd_claim'ed the block_device* to use this.  NOTE:  bd_claim allows an owner to claim* the same device multiple times, the owner must take special* care to not mess up bd_private for that case.*/unsigned long		bd_private;/* The counter of freeze processes */int			bd_fsfreeze_count;/* Mutex for freeze */struct mutex		bd_fsfreeze_mutex;
};

1、块设备注册

/*** register_blkdev - register a new block device** @major: the requested major device number [1..255]. If @major=0, try to*         allocate any unused major number.* @name: the name of the new block device as a zero terminated string** The @name must be unique within the system.** The return value depends on the @major input parameter.*  - if a major device number was requested in range [1..255] then the*    function returns zero on success, or a negative error code*  - if any unused major number was requested with @major=0 parameter*    then the return value is the allocated major number in range*    [1..255] or a negative error code otherwise*/
int register_blkdev(unsigned int major, const char *name)

2、块设备注销

void unregister_blkdev(unsigned int major, const char *name)

2、实际块设备

struct gendisk {/* major, first_minor and minors are input parameters only,* don't use directly.  Use disk_devt() and disk_max_parts().*/int major;			/* major number of driver */int first_minor;int minors;                     /* maximum number of minors, =1 for* disks that can't be partitioned. */char disk_name[DISK_NAME_LEN];	/* name of major driver */char *(*devnode)(struct gendisk *gd, umode_t *mode);unsigned int events;		/* supported events */unsigned int async_events;	/* async events, subset of all *//* Array of pointers to partitions indexed by partno.* Protected with matching bdev lock but stat and other* non-critical accesses use RCU.  Always access through* helpers.*/struct disk_part_tbl __rcu *part_tbl;struct hd_struct part0;const struct block_device_operations *fops;struct request_queue *queue;void *private_data;int flags;struct device *driverfs_dev;  // FIXME: removestruct kobject *slave_dir;struct timer_rand_state *random;atomic_t sync_io;		/* RAID */struct disk_events *ev;
#ifdef  CONFIG_BLK_DEV_INTEGRITYstruct blk_integrity *integrity;
#endifint node_id;
};

1、申请 gendisk

struct gendisk *alloc_disk(int minors)

2、删除 gendisk

void del_gendisk(struct gendisk *disk)

3、将 gendisk 添加到内核

void add_disk(struct gendisk *disk)

4、设置 gendisk 容量

void set_capacity(struct gendisk *disk, sector_t size)

5、调整 gendisk 引用计数

truct kobject *get_disk(struct gendisk *disk)
void put_disk(struct gendisk *disk)

3、block_device 和 gendisk 区别

struct block_device：用来描述一个块设备或者块设备的一个分区。与文件系统关系密切。

struct gendisk：描述整个块设备的特性。块设备驱动程序的主要操作对象。

对于一个包含多个分区的块设备，struct block_device 结构有多个，而 struct gendisk 结构只有一个。

4、块设备操作集

struct block_device_operations {int (*open) (struct block_device *, fmode_t);void (*release) (struct gendisk *, fmode_t);int (*rw_page)(struct block_device *, sector_t, struct page *, int rw);int (*ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);int (*compat_ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);long (*direct_access)(struct block_device *, sector_t,void **, unsigned long *pfn, long size);unsigned int (*check_events) (struct gendisk *disk,unsigned int clearing);/* ->media_changed() is DEPRECATED, use ->check_events() instead */int (*media_changed) (struct gendisk *);void (*unlock_native_capacity) (struct gendisk *);int (*revalidate_disk) (struct gendisk *);int (*getgeo)(struct block_device *, struct hd_geometry *);/* this callback is with swap_lock and sometimes page table lock held */void (*swap_slot_free_notify) (struct block_device *, unsigned long);struct module *owner;
};

5、请求队列

struct request_queue {/** Together with queue_head for cacheline sharing*/struct list_head	queue_head;struct request		*last_merge;struct elevator_queue	*elevator;int			nr_rqs[2];	/* # allocated [a]sync rqs */int			nr_rqs_elvpriv;	/* # allocated rqs w/ elvpriv *//** If blkcg is not used, @q->root_rl serves all requests.  If blkcg* is used, root blkg allocates from @q->root_rl and all other* blkgs from their own blkg->rl.  Which one to use should be* determined using bio_request_list().*/struct request_list	root_rl;request_fn_proc		*request_fn;make_request_fn		*make_request_fn;prep_rq_fn		*prep_rq_fn;unprep_rq_fn		*unprep_rq_fn;merge_bvec_fn		*merge_bvec_fn;softirq_done_fn		*softirq_done_fn;rq_timed_out_fn		*rq_timed_out_fn;dma_drain_needed_fn	*dma_drain_needed;lld_busy_fn		*lld_busy_fn;struct blk_mq_ops	*mq_ops;unsigned int		*mq_map;/* sw queues */struct blk_mq_ctx __percpu	*queue_ctx;unsigned int		nr_queues;/* hw dispatch queues */struct blk_mq_hw_ctx	**queue_hw_ctx;unsigned int		nr_hw_queues;/** Dispatch queue sorting*/sector_t		end_sector;struct request		*boundary_rq;/** Delayed queue handling*/struct delayed_work	delay_work;struct backing_dev_info	backing_dev_info;/** The queue owner gets to use this for whatever they like.* ll_rw_blk doesn't touch it.*/void			*queuedata;/** various queue flags, see QUEUE_* below*/unsigned long		queue_flags;/** ida allocated id for this queue.  Used to index queues from* ioctx.*/int			id;/** queue needs bounce pages for pages above this limit*/gfp_t			bounce_gfp;/** protects queue structures from reentrancy. ->__queue_lock should* _never_ be used directly, it is queue private. always use* ->queue_lock.*/spinlock_t		__queue_lock;spinlock_t		*queue_lock;/** queue kobject*/struct kobject kobj;/** mq queue kobject*/struct kobject mq_kobj;#ifdef CONFIG_PMstruct device		*dev;int			rpm_status;unsigned int		nr_pending;
#endif/** queue settings*/unsigned long		nr_requests;	/* Max # of requests */unsigned int		nr_congestion_on;unsigned int		nr_congestion_off;unsigned int		nr_batching;unsigned int		dma_drain_size;void			*dma_drain_buffer;unsigned int		dma_pad_mask;unsigned int		dma_alignment;struct blk_queue_tag	*queue_tags;struct list_head	tag_busy_list;unsigned int		nr_sorted;unsigned int		in_flight[2];/** Number of active block driver functions for which blk_drain_queue()* must wait. Must be incremented around functions that unlock the* queue_lock internally, e.g. scsi_request_fn().*/unsigned int		request_fn_active;unsigned int		rq_timeout;struct timer_list	timeout;struct list_head	timeout_list;struct list_head	icq_list;
#ifdef CONFIG_BLK_CGROUPDECLARE_BITMAP		(blkcg_pols, BLKCG_MAX_POLS);struct blkcg_gq		*root_blkg;struct list_head	blkg_list;
#endifstruct queue_limits	limits;/** sg stuff*/unsigned int		sg_timeout;unsigned int		sg_reserved_size;int			node;
#ifdef CONFIG_BLK_DEV_IO_TRACEstruct blk_trace	*blk_trace;
#endif/** for flush operations*/unsigned int		flush_flags;unsigned int		flush_not_queueable:1;struct blk_flush_queue	*fq;struct list_head	requeue_list;spinlock_t		requeue_lock;struct work_struct	requeue_work;struct mutex		sysfs_lock;int			bypass_depth;int			mq_freeze_depth;#if defined(CONFIG_BLK_DEV_BSG)bsg_job_fn		*bsg_job_fn;int			bsg_job_size;struct bsg_class_device bsg_dev;
#endif#ifdef CONFIG_BLK_DEV_THROTTLING/* Throttle data */struct throtl_data *td;
#endifstruct rcu_head		rcu_head;wait_queue_head_t	mq_freeze_wq;struct percpu_ref	mq_usage_counter;struct list_head	all_q_node;struct blk_mq_tag_set	*tag_set;struct list_head	tag_set_list;
};

request_queue 对象表示针对一个 gendisk 对象的所有请求的队列。

1、初始化请求队列

struct request_queue *blk_init_queue(request_fn_proc *, spinlock_t *);

2、删除请求队列

void blk_cleanup_queue(struct request_queue *);

3、制造请求函数

void blk_queue_make_request(struct request_queue *, make_request_fn *);

6、请求项

/** Try to put the fields that are referenced together in the same cacheline.** If you modify this structure, make sure to update blk_rq_init() and* especially blk_mq_rq_ctx_init() to take care of the added fields.*/
struct request {struct list_head queuelist;union {struct call_single_data csd;unsigned long fifo_time;};struct request_queue *q;struct blk_mq_ctx *mq_ctx;u64 cmd_flags;enum rq_cmd_type_bits cmd_type;unsigned long atomic_flags;int cpu;/* the following two fields are internal, NEVER access directly */unsigned int __data_len;	/* total data len */sector_t __sector;		/* sector cursor */struct bio *bio;struct bio *biotail;/** The hash is used inside the scheduler, and killed once the* request reaches the dispatch list. The ipi_list is only used* to queue the request for softirq completion, which is long* after the request has been unhashed (and even removed from* the dispatch list).*/union {struct hlist_node hash;	/* merge hash */struct list_head ipi_list;};/** The rb_node is only used inside the io scheduler, requests* are pruned when moved to the dispatch queue. So let the* completion_data share space with the rb_node.*/union {struct rb_node rb_node;	/* sort/lookup */void *completion_data;};/** Three pointers are available for the IO schedulers, if they need* more they have to dynamically allocate it.  Flush requests are* never put on the IO scheduler. So let the flush fields share* space with the elevator data.*/union {struct {struct io_cq		*icq;void			*priv[2];} elv;struct {unsigned int		seq;struct list_head	list;rq_end_io_fn		*saved_end_io;} flush;};struct gendisk *rq_disk;struct hd_struct *part;unsigned long start_time;
#ifdef CONFIG_BLK_CGROUPstruct request_list *rl;		/* rl this rq is alloced from */unsigned long long start_time_ns;unsigned long long io_start_time_ns;    /* when passed to hardware */
#endif/* Number of scatter-gather DMA addr+len pairs after* physical address coalescing is performed.*/unsigned short nr_phys_segments;
#if defined(CONFIG_BLK_DEV_INTEGRITY)unsigned short nr_integrity_segments;
#endifunsigned short ioprio;void *special;		/* opaque pointer available for LLD use */int tag;int errors;/** when request is used as a packet command carrier*/unsigned char __cmd[BLK_MAX_CDB];unsigned char *cmd;unsigned short cmd_len;unsigned int extra_len;	/* length of alignment and padding */unsigned int sense_len;unsigned int resid_len;	/* residual count */void *sense;unsigned long deadline;struct list_head timeout_list;unsigned int timeout;int retries;/** completion callback.*/rq_end_io_fn *end_io;void *end_io_data;/* for bidi */struct request *next_rq;
};

1、获取请求

struct request *blk_peek_request(struct request_queue *q);

2、开启请求

void blk_start_request(struct request *req)

3、获取、开启请求

struct request *blk_fetch_request(struct request_queue *q)

7、bio

/** main unit of I/O for the block layer and lower layers (ie drivers and* stacking drivers)*/
struct bio {struct bio		*bi_next;	/* request queue link */struct block_device	*bi_bdev;unsigned long		bi_flags;	/* status, command, etc */unsigned long		bi_rw;		/* bottom bits READ/WRITE,* top bits priority*/struct bvec_iter	bi_iter;/* Number of segments in this BIO after* physical address coalescing is performed.*/unsigned int		bi_phys_segments;/** To keep track of the max segment size, we account for the* sizes of the first and last mergeable segments in this bio.*/unsigned int		bi_seg_front_size;unsigned int		bi_seg_back_size;atomic_t		bi_remaining;bio_end_io_t		*bi_end_io;void			*bi_private;
#ifdef CONFIG_BLK_CGROUP/** Optional ioc and css associated with this bio.  Put on bio* release.  Read comment on top of bio_associate_current().*/struct io_context	*bi_ioc;struct cgroup_subsys_state *bi_css;
#endifunion {
#if defined(CONFIG_BLK_DEV_INTEGRITY)struct bio_integrity_payload *bi_integrity; /* data integrity */
#endif};unsigned short		bi_vcnt;	/* how many bio_vec's *//** Everything starting with bi_max_vecs will be preserved by bio_reset()*/unsigned short		bi_max_vecs;	/* max bvl_vecs we can hold */atomic_t		bi_cnt;		/* pin count */struct bio_vec		*bi_io_vec;	/* the actual vec list */struct bio_set		*bi_pool;/** We can inline a number of vecs at the end of the bio, to avoid* double allocations for a small number of bio_vecs. This member* MUST obviously be kept at the very end of the bio.*/struct bio_vec		bi_inline_vecs[0];
};

1、遍历 bio

#define __rq_for_each_bio(_bio, rq)

2、遍历 bio 中所有段

#define bio_for_each_segment(bvl, bio, iter)

3、通知 bio 处理结束

bvoid bio_endio(struct bio *bio, int error)

8、硬件信息(bvec_iter)

struct bvec_iter {sector_t		bi_sector;	/* device address in 512 bytesectors */unsigned int		bi_size;	/* residual I/O count */unsigned int		bi_idx;		/* current index into bvl_vec */unsigned int            bi_bvec_done;	/* number of bytes completed incurrent bvec */
};

9、bio_vec

/** was unsigned short, but we might as well be ready for > 64kB I/O pages*/
struct bio_vec {struct page	*bv_page;unsigned int	bv_len;unsigned int	bv_offset;
};

10、bio逻辑架构

11、request_queue、request和bio关系

五、内存模拟硬盘驱动编写(使用内核请求队列)

参考：drivers\block\z2ram.c。

1、编写思路

1、从 RAM 中分配内存。

2、注册逻辑块设备，为应用层提供操作对象。

3、初始化请求队列。

4、添加、初始化实际块设备，为驱动提供操作对象。

5、通过注册的请求队列函数进行数据传输（可以使用内核提供，也可以自己进行构造）。

2、驱动实现

#include "linux/init.h"
#include "linux/module.h"
#include "linux/slab.h"
#include "linux/spinlock_types.h"
#include "linux/fs.h"
#include "linux/genhd.h"
#include "linux/hdreg.h"
#include "linux/blkdev.h"#define RAMDISK_SIZE	(2 * 1024 * 1024) 	/* 容量大小为2MB */
#define RAMDISK_NAME	"ramdisk"			/* 名字 */
#define RADMISK_MINOR	3					/* 表示有三个磁盘分区！不是次设备号为3！ */typedef struct{unsigned char *ramdiskbuf;	/* ramdisk内存空间,用于模拟块设备 */spinlock_t lock;			/* 自旋锁 */int major;					/* 主设备号 */struct request_queue *queue;/* 请求队列 */struct gendisk *gendisk; 	/* gendisk */
}newchrdev_t;
newchrdev_t newchrdev;/** @description		: 打开块设备* @param - dev 	: 块设备* @param - mode 	: 打开模式* @return 			: 0 成功;其他 失败*/
int ramdisk_open(struct block_device *dev, fmode_t mode)
{printk("ramdisk open\r\n");return 0;
}/** @description		: 释放块设备* @param - disk 	: gendisk* @param - mode 	: 模式* @return 			: 0 成功;其他 失败*/
void ramdisk_release(struct gendisk *disk, fmode_t mode)
{printk("ramdisk release\r\n");
}/** @description		: 获取磁盘信息* @param - dev 	: 块设备* @param - geo 	: 模式* @return 			: 0 成功;其他 失败*/
int ramdisk_getgeo(struct block_device *dev, struct hd_geometry *geo)
{/* 这是相对于机械硬盘的概念 */geo->heads = 2;			/* 磁头 */geo->cylinders = 32;	/* 柱面 */geo->sectors = RAMDISK_SIZE / (2 * 32 *512); /* 一个磁道上的扇区数量 */return 0;
}/* * 块设备操作函数 */
static struct block_device_operations ramdisk_fops =
{.owner	 = THIS_MODULE,.open	 = ramdisk_open,.release = ramdisk_release,.getgeo  = ramdisk_getgeo,
};/** @description	: 处理传输过程* @param-req 	: 请求* @return 		: 无*/
static void ramdisk_transfer(struct request *req)
{	unsigned long start = blk_rq_pos(req) << 9;  	/* blk_rq_pos获取到的是扇区地址，左移9位转换为字节地址 */unsigned long len  = blk_rq_cur_bytes(req);		/* 大小   *//* bio中的数据缓冲区* 读：从磁盘读取到的数据存放到buffer中* 写：buffer保存这要写入磁盘的数据*/void *buffer = bio_data(req->bio);		if(rq_data_dir(req) == READ) 		/* 读数据 *//* 不同块设备，具体操作不同，RAM才可以使用memcpy进行处理 */memcpy(buffer, newchrdev.ramdiskbuf + start, len);else if(rq_data_dir(req) == WRITE) 	/* 写数据 */memcpy(newchrdev.ramdiskbuf + start, buffer, len);}/** @description	: 请求处理函数* @param-q 	: 请求队列* @return 		: 无*/
void ramdisk_request_fn(struct request_queue *q)
{int err = 0;struct request *req;/* 循环处理请求队列中的每个请求 */req = blk_fetch_request(q);while(req != NULL) {/* 针对请求做具体的传输处理 */ramdisk_transfer(req);/* 判断是否为最后一个请求，如果不是的话就获取下一个请求* 循环处理完请求队列中的所有请求。*/if (!__blk_end_request_cur(req, err))req = blk_fetch_request(q);}
}/** @description	: 驱动出口函数* @param 		: 无* @return 		: 无*/
static int __init ramdisk_init(void)
{int ret = 0;printk("ramdisk init\r\n");/* 1、申请用于ramdisk内存 */newchrdev.ramdiskbuf = kzalloc(RAMDISK_SIZE, GFP_KERNEL);if(newchrdev.ramdiskbuf == NULL) {ret = -EINVAL;goto ram_fail;}/* 2、初始化自旋锁 */spin_lock_init(&newchrdev.lock);/* 3、注册块设备(逻辑块设备：为应用层提供一个操作对象) */newchrdev.major = register_blkdev(0, RAMDISK_NAME); /* 由系统自动分配主设备号 */if(newchrdev.major < 0) {goto register_blkdev_fail;}  printk("ramdisk major = %d\r\n", newchrdev.major);/* 4、分配并初始化gendisk */newchrdev.gendisk = alloc_disk(RADMISK_MINOR);if(!newchrdev.gendisk) {ret = -EINVAL;goto gendisk_alloc_fail;}/* 5、分配并初始化请求队列 */newchrdev.queue = blk_init_queue(ramdisk_request_fn, &newchrdev.lock);if(!newchrdev.queue) {ret = EINVAL;goto blk_init_fail;}/* 6、添加(注册)disk* (1)、关联逻辑块设备和物理块设备* (2)、为物理块设备添加操作集和请求队列* (3)、为物理块设备设置属性*/newchrdev.gendisk->major = newchrdev.major;		/* 主设备号 */newchrdev.gendisk->first_minor = 0;			/* 第一个次设备号(起始次设备号) */newchrdev.gendisk->fops = &ramdisk_fops; 		/* 操作函数 */newchrdev.gendisk->private_data = &newchrdev;	/* 私有数据 */newchrdev.gendisk->queue = newchrdev.queue;		/* 请求队列 */sprintf(newchrdev.gendisk->disk_name, RAMDISK_NAME); /* 名字 */set_capacity(newchrdev.gendisk, RAMDISK_SIZE/512);	/* 设备容量(单位为扇区) */add_disk(newchrdev.gendisk);return 0;
blk_init_fail:put_disk(newchrdev.gendisk);//del_gendisk(ramdisk.gendisk);
gendisk_alloc_fail:unregister_blkdev(newchrdev.major, RAMDISK_NAME);
register_blkdev_fail:kfree(newchrdev.ramdiskbuf); /* 释放内存 */
ram_fail:return ret;
}/** @description	: 驱动出口函数* @param 		: 无* @return 		: 无*/
static void __exit ramdisk_exit(void)
{printk("ramdisk exit\r\n");/* 释放gendisk */del_gendisk(newchrdev.gendisk);put_disk(newchrdev.gendisk);/* 清除请求队列 */blk_cleanup_queue(newchrdev.queue);/* 注销块设备 */unregister_blkdev(newchrdev.major, RAMDISK_NAME);/* 释放内存 */kfree(newchrdev.ramdiskbuf); 
}module_init(ramdisk_init);
module_exit(ramdisk_exit);
MODULE_LICENSE("GPL");

3、测试

# ls
ramdisk.ko
#
# insmod ramdisk.ko
ramdisk init
ramdisk major = 254
ramdisk open
ramdisk release
#
# ls -l /dev/ramdisk
brw-rw----    1 root     root      254,   0 Jan  1 00:13 /dev/ramdisk
#
# rmmod ramdisk.ko
ramdisk exit
#
# ls -l /dev/ramdisk
ls: /dev/ramdisk: No such file or directory
#
# insmod ramdisk.ko
ramdisk init
ramdisk major = 254
ramdisk open
ramdisk release
#
# rmmod ramdisk.ko
ramdisk exit
#
# insmod ramdisk.ko
ramdisk init
ramdisk major = 254
ramdisk open
ramdisk release
# ls -l /dev/ramdisk
brw-rw----    1 root     root      254,   0 Jan  1 00:14 /dev/ramdisk
#
# fdisk -l
Disk /dev/mmcblk0: 15 GB, 15931539456 bytes, 31116288 sectors
1936 cylinders, 255 heads, 63 sectors/track
Units: sectors of 1 * 512 = 512 bytesDevice       ramdisk open
Boot StartCHS    EndCHS        Stramdisk release
artLBA     EndLBA    Sectors  Sizramdisk open
e Id Type
/dev/mmcblk0p1    0,13ramdisk release
0,3     1023,254,63       8192   31116287   31108096 14.8G  c Win95 FAT32 (LBA)
Disk /dev/mmcblk1: 7456 MB, 7818182656 bytes, 15269888 sectors
238592 cylinders, 4 heads, 16 sectors/track
Units: sectors of 1 * 512 = 512 bytesDevice       Boot StartCHS    EndCHS        StartLBA     EndLBA    Sectors  Size Id Type
/dev/mmcblk1p1 *  0,32,33     4,52,48           2048      67583      65536 32.0M  c Win95 FAT32 (LBA)
/dev/mmcblk1p2    4,52,49     950,129,11       67584   15269887   15202304 7423M 83 Linux
Disk /dev/mmcblk1boot1: 4 MB, 4194304 bytes, 8192 sectors
128 cylinders, 4 heads, 16 sectors/track
Units: sectors of 1 * 512 = 512 bytesDisk /dev/mmcblk1boot1 doesn't contain a valid partition table
Disk /dev/mmcblk1boot0: 4 MB, 4194304 bytes, 8192 sectors
128 cylinders, 4 heads, 16 sectors/track
Units: sectors of 1 * 512 = 512 bytesDisk /dev/mmcblk1boot0 doesn't contain a valid partition table
Disk /dev/ramdisk: 2 MB, 2097152 bytes, 4096 sectors
32 cylinders, 2 heads, 64 sectors/track
Units: sectors of 1 * 512 = 512 bytesDisk /dev/ramdisk doesn't contain a valid partition table
#

六、内存模拟硬盘驱动编写(自定义请求队列)

参考：drivers\block\zram\zram_drv.c。

1、编写思路

1、从 RAM 中分配内存。

2、注册逻辑块设备，为应用层提供操作对象。

3、设置“制造请求”函数。

4、添加、初始化实际块设备，为驱动提供操作对象。

5、通过注册的请求队列函数进行数据传输（可以使用内核提供，也可以自己进行构造）。

2、驱动实现

#include "linux/init.h"
#include "linux/module.h"
#include "linux/slab.h"
#include "linux/spinlock_types.h"
#include "linux/fs.h"
#include "linux/genhd.h"
#include "linux/hdreg.h"
#include "linux/blkdev.h"#define RAMDISK_SIZE	(2 * 1024 * 1024) 	/* 容量大小为2MB */
#define RAMDISK_NAME	"ramdisk"			/* 名字 */
#define RADMISK_MINOR	3					/* 表示有三个磁盘分区！不是次设备号为3！ */typedef struct{unsigned char *ramdiskbuf;	/* ramdisk内存空间,用于模拟块设备 */spinlock_t lock;			/* 自旋锁 */int major;					/* 主设备号 */struct request_queue *queue;/* 请求队列 */struct gendisk *gendisk; 	/* gendisk */
}newchrdev_t;
newchrdev_t newchrdev;/** @description		: 打开块设备* @param - dev 	: 块设备* @param - mode 	: 打开模式* @return 			: 0 成功;其他 失败*/
int ramdisk_open(struct block_device *dev, fmode_t mode)
{printk("ramdisk open\r\n");return 0;
}/** @description		: 释放块设备* @param - disk 	: gendisk* @param - mode 	: 模式* @return 			: 0 成功;其他 失败*/
void ramdisk_release(struct gendisk *disk, fmode_t mode)
{printk("ramdisk release\r\n");
}/** @description		: 获取磁盘信息* @param - dev 	: 块设备* @param - geo 	: 模式* @return 			: 0 成功;其他 失败*/
int ramdisk_getgeo(struct block_device *dev, struct hd_geometry *geo)
{/* 这是相对于机械硬盘的概念 */geo->heads = 2;			/* 磁头 */geo->cylinders = 32;	/* 柱面 */geo->sectors = RAMDISK_SIZE / (2 * 32 *512); /* 一个磁道上的扇区数量 */return 0;
}/* * 块设备操作函数 */
static struct block_device_operations ramdisk_fops =
{.owner	 = THIS_MODULE,.open	 = ramdisk_open,.release = ramdisk_release,.getgeo  = ramdisk_getgeo,
};#if 0
/** @description	: 处理传输过程* @param-req 	: 请求* @return 		: 无*/
static void ramdisk_transfer(struct request *req)
{	unsigned long start = blk_rq_pos(req) << 9;  	/* blk_rq_pos获取到的是扇区地址，左移9位转换为字节地址 */unsigned long len  = blk_rq_cur_bytes(req);		/* 大小   *//* bio中的数据缓冲区* 读：从磁盘读取到的数据存放到buffer中* 写：buffer保存这要写入磁盘的数据*/void *buffer = bio_data(req->bio);		if(rq_data_dir(req) == READ) 		/* 读数据 *//* 不同块设备，具体操作不同，RAM才可以使用memcpy进行处理 */memcpy(buffer, newchrdev.ramdiskbuf + start, len);else if(rq_data_dir(req) == WRITE) 	/* 写数据 */memcpy(newchrdev.ramdiskbuf + start, buffer, len);}/** @description	: 请求处理函数* @param-q 	: 请求队列* @return 		: 无*/
void ramdisk_request_fn(struct request_queue *q)
{int err = 0;struct request *req;/* 循环处理请求队列中的每个请求 */req = blk_fetch_request(q);while(req != NULL) {/* 针对请求做具体的传输处理 */ramdisk_transfer(req);/* 判断是否为最后一个请求，如果不是的话就获取下一个请求* 循环处理完请求队列中的所有请求。*/if (!__blk_end_request_cur(req, err))req = blk_fetch_request(q);}
}
#endif/** @description	: “制造请求”函数* @param-q 	: 请求队列* @return 		: 无*/
void ramdisk_make_request_fn(struct request_queue *q, struct bio *bio)
{int offset;struct bio_vec bvec;struct bvec_iter iter;unsigned long len = 0;offset = (bio->bi_iter.bi_sector) << 9;	/* 获取要操作的设备的偏移地址 *//* 处理bio中的每个段 */bio_for_each_segment(bvec, bio, iter){char *ptr = page_address(bvec.bv_page) + bvec.bv_offset;len = bvec.bv_len;if(bio_data_dir(bio) == READ)	/* 读数据 *//* 不同块设备，具体操作不同，RAM才可以使用memcpy进行处理 */memcpy(ptr, newchrdev.ramdiskbuf + offset, len);else if(bio_data_dir(bio) == WRITE)	/* 写数据 */memcpy(newchrdev.ramdiskbuf + offset, ptr, len);offset += len;}set_bit(BIO_UPTODATE, &bio->bi_flags);bio_endio(bio, 0);
}/** @description	: 驱动出口函数* @param 		: 无* @return 		: 无*/
static int __init ramdisk_init(void)
{int ret = 0;printk("ramdisk init\r\n");/* 1、申请用于ramdisk内存 */newchrdev.ramdiskbuf = kzalloc(RAMDISK_SIZE, GFP_KERNEL);if(newchrdev.ramdiskbuf == NULL) {ret = -EINVAL;goto ram_fail;}/* 2、初始化自旋锁 */spin_lock_init(&newchrdev.lock);/* 3、注册块设备(逻辑块设备：为应用层提供一个操作对象) */newchrdev.major = register_blkdev(0, RAMDISK_NAME); /* 由系统自动分配主设备号 */if(newchrdev.major < 0) {goto register_blkdev_fail;}  printk("ramdisk major = %d\r\n", newchrdev.major);/* 4、分配并初始化gendisk */newchrdev.gendisk = alloc_disk(RADMISK_MINOR);if(!newchrdev.gendisk) {ret = -EINVAL;goto gendisk_alloc_fail;}/* 5、分配并初始化请求队列 */
#if 0newchrdev.queue = blk_init_queue(ramdisk_request_fn, &newchrdev.lock);if(!newchrdev.queue) {ret = EINVAL;goto blk_init_fail;}
#endifnewchrdev.queue = blk_alloc_queue(GFP_KERNEL);if(!newchrdev.queue){ret = -EINVAL;goto blk_allo_fail;}/* 6、设置“制造请求”函数 */blk_queue_make_request(newchrdev.queue, ramdisk_make_request_fn);/* 7、添加(注册)disk* (1)、关联逻辑块设备和物理块设备* (2)、为物理块设备添加操作集和请求队列* (3)、为物理块设备设置属性*/newchrdev.gendisk->major = newchrdev.major;		/* 主设备号 */newchrdev.gendisk->first_minor = 0;			/* 第一个次设备号(起始次设备号) */newchrdev.gendisk->fops = &ramdisk_fops; 		/* 操作函数 */newchrdev.gendisk->private_data = &newchrdev;	/* 私有数据 */newchrdev.gendisk->queue = newchrdev.queue;		/* 请求队列 */sprintf(newchrdev.gendisk->disk_name, RAMDISK_NAME); /* 名字 */set_capacity(newchrdev.gendisk, RAMDISK_SIZE/512);	/* 设备容量(单位为扇区) */add_disk(newchrdev.gendisk);return 0;
blk_allo_fail:put_disk(newchrdev.gendisk);//del_gendisk(ramdisk.gendisk);
gendisk_alloc_fail:unregister_blkdev(newchrdev.major, RAMDISK_NAME);
register_blkdev_fail:kfree(newchrdev.ramdiskbuf); /* 释放内存 */
ram_fail:return ret;
}/** @description	: 驱动出口函数* @param 		: 无* @return 		: 无*/
static void __exit ramdisk_exit(void)
{printk("ramdisk exit\r\n");/* 释放gendisk */del_gendisk(newchrdev.gendisk);put_disk(newchrdev.gendisk);/* 清除请求队列 */blk_cleanup_queue(newchrdev.queue);/* 注销块设备 */unregister_blkdev(newchrdev.major, RAMDISK_NAME);/* 释放内存 */kfree(newchrdev.ramdiskbuf); 
}module_init(ramdisk_init);
module_exit(ramdisk_exit);
MODULE_LICENSE("GPL");

3、测试

# ls
ramdisk.ko
# insmod ramdisk.ko
ramdisk init
ramdisk major = 254
ramdisk open
ramdisk release
# ls -l /dev/ramdisk
brw-rw----    1 root     root      254,   0 Jan  1 00:51 /dev/ramdisk
#
# rmmod ramdisk.ko
ramdisk exit
#
# ls -l /dev/ramdisk
ls: /dev/ramdisk: No such file or directory
#
# insmod ramdisk.ko
ramdisk init
ramdisk major = 254
ramdisk open
ramdisk release
#
# ls -l /dev/ramdisk
brw-rw----    1 root     root      254,   0 Jan  1 00:51 /dev/ramdisk
#
# rmmod ramdisk.ko
ramdisk exit
#
# random: nonblocking pool is initialized
# ls -l /dev/ramdisk
ls: /dev/ramdisk: No such file or directory
#
#
#
# insmod ramdisk.ko
ramdisk init
ramdisk major = 254
ramdisk open
ramdisk release
#
# fdisk -l
Disk /dev/mmcblk0: 15 GB, 15931539456 bytes, 31116288 sectors
1936 cylinders, 255 heads, 63 sectors/track
Units: sectors of 1 * 512 = 512 bytesDevice       Boot StartCHS    EndCHS        Sramdisk open
tartLBA     EndLBA    Sectors  Siramdisk release
ze Id Type
/dev/mmcblk0p1    0,1ramdisk open
30,3     1023,254,63       8192   31116287   31108096 14.8G  c Wiramdisk release
n95 FAT32 (LBA)
Disk /dev/mmcblk1: 7456 MB, 7818182656 bytes, 15269888 sectors
238592 cylinders, 4 heads, 16 sectors/track
Units: sectors of 1 * 512 = 512 bytesDevice       Boot StartCHS    EndCHS        StartLBA     EndLBA    Sectors  Size Id Type
/dev/mmcblk1p1 *  0,32,33     4,52,48           2048      67583      65536 32.0M  c Win95 FAT32 (LBA)
/dev/mmcblk1p2    4,52,49     950,129,11       67584   15269887   15202304 7423M 83 Linux
Disk /dev/mmcblk1boot1: 4 MB, 4194304 bytes, 8192 sectors
128 cylinders, 4 heads, 16 sectors/track
Units: sectors of 1 * 512 = 512 bytesDisk /dev/mmcblk1boot1 doesn't contain a valid partition table
Disk /dev/mmcblk1boot0: 4 MB, 4194304 bytes, 8192 sectors
128 cylinders, 4 heads, 16 sectors/track
Units: sectors of 1 * 512 = 512 bytesDisk /dev/mmcblk1boot0 doesn't contain a valid partition table
Disk /dev/ramdisk: 2 MB, 2097152 bytes, 4096 sectors
32 cylinders, 2 heads, 64 sectors/track
Units: sectors of 1 * 512 = 512 bytesDisk /dev/ramdisk doesn't contain a valid partition table
#