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_tbd_dev; /* not a kdev_t - it's a search key */intbd_openers;struct inode *bd_inode;/* will die */struct super_block *bd_super;struct mutexbd_mutex;/* open/close mutex */struct list_headbd_inodes;void *bd_claiming;void *bd_holder;intbd_holders;boolbd_write_holder;#ifdef CONFIG_SYSFSstruct list_headbd_holder_disks;#endifstruct block_device *bd_contains;unsignedbd_block_size;struct hd_struct *bd_part;/* number of times partitions within this device have been opened. */unsignedbd_part_count;intbd_invalidated;struct gendisk *bd_disk;struct request_queue * bd_queue;struct list_headbd_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 longbd_private;/* The counter of freeze processes */intbd_fsfreeze_count;/* Mutex for freeze */struct mutexbd_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_headqueue_head;struct request*last_merge;struct elevator_queue*elevator;intnr_rqs[2];/* # allocated [a]sync rqs */intnr_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_listroot_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 intnr_queues;/* hw dispatch queues */struct blk_mq_hw_ctx**queue_hw_ctx;unsigned intnr_hw_queues;/* * Dispatch queue sorting */sector_tend_sector;struct request*boundary_rq;/* * Delayed queue handling */struct delayed_workdelay_work;struct backing_dev_infobacking_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 longqueue_flags;/* * ida allocated id for this queue. Used to index queues from * ioctx. */intid;/* * queue needs bounce pages for pages above this limit */gfp_tbounce_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;intrpm_status;unsigned intnr_pending;#endif/* * queue settings */unsigned longnr_requests;/* Max # of requests */unsigned intnr_congestion_on;unsigned intnr_congestion_off;unsigned intnr_batching;unsigned intdma_drain_size;void*dma_drain_buffer;unsigned intdma_pad_mask;unsigned intdma_alignment;struct blk_queue_tag*queue_tags;struct list_headtag_busy_list;unsigned intnr_sorted;unsigned intin_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 intrequest_fn_active;unsigned intrq_timeout;struct timer_listtimeout;struct list_headtimeout_list;struct list_headicq_list;#ifdef CONFIG_BLK_CGROUPDECLARE_BITMAP(blkcg_pols, BLKCG_MAX_POLS);struct blkcg_gq*root_blkg;struct list_headblkg_list;#endifstruct queue_limitslimits;/* * sg stuff */unsigned intsg_timeout;unsigned intsg_reserved_size;intnode;#ifdef CONFIG_BLK_DEV_IO_TRACEstruct blk_trace*blk_trace;#endif/* * for flush operations */unsigned intflush_flags;unsigned intflush_not_queueable:1;struct blk_flush_queue*fq;struct list_headrequeue_list;spinlock_trequeue_lock;struct work_structrequeue_work;struct mutexsysfs_lock;intbypass_depth;intmq_freeze_depth;#if defined(CONFIG_BLK_DEV_BSG)bsg_job_fn*bsg_job_fn;intbsg_job_size;struct bsg_class_device bsg_dev;#endif#ifdef CONFIG_BLK_DEV_THROTTLING/* Throttle data */struct throtl_data *td;#endifstruct rcu_headrcu_head;wait_queue_head_tmq_freeze_wq;struct percpu_refmq_usage_counter;struct list_headall_q_node;struct blk_mq_tag_set*tag_set;struct list_headtag_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 intseq;struct list_headlist;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 longbi_flags;/* status, command, etc */unsigned longbi_rw;/* bottom bits READ/WRITE, * top bits priority */struct bvec_iterbi_iter;/* Number of segments in this BIO after * physical address coalescing is performed. */unsigned intbi_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 intbi_seg_front_size;unsigned intbi_seg_back_size;atomic_tbi_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 shortbi_vcnt;/* how many bio_vec's *//* * Everything starting with bi_max_vecs will be preserved by bio_reset() */unsigned shortbi_max_vecs;/* max bvl_vecs we can hold */atomic_tbi_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_vecbi_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_tbi_sector;/* device address in 512 byte sectors */unsigned intbi_size;/* residual I/O count */unsigned intbi_idx;/* current index into bvl_vec */unsigned int bi_bvec_done;/* number of bytes completed in current 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 intbv_len;unsigned intbv_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_MINOR3/* 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
# lsramdisk.ko## insmod ramdisk.koramdisk initramdisk major = 254ramdisk openramdisk release## ls -l /dev/ramdiskbrw-rw---- 1 root root 254, 0 Jan 1 00:13 /dev/ramdisk## rmmod ramdisk.koramdisk exit## ls -l /dev/ramdiskls: /dev/ramdisk: No such file or directory## insmod ramdisk.koramdisk initramdisk major = 254ramdisk openramdisk release## rmmod ramdisk.koramdisk exit## insmod ramdisk.koramdisk initramdisk major = 254ramdisk openramdisk release# ls -l /dev/ramdiskbrw-rw---- 1 root root 254, 0 Jan 1 00:14 /dev/ramdisk## fdisk -lDisk /dev/mmcblk0: 15 GB, 15931539456 bytes, 31116288 sectors1936 cylinders, 255 heads, 63 sectors/trackUnits: sectors of 1 * 512 = 512 bytesDevice ramdisk openBoot StartCHS EndCHS Stramdisk releaseartLBA EndLBA Sectors Sizramdisk opene Id Type/dev/mmcblk0p1 0,13ramdisk release0,3 1023,254,63 8192 31116287 31108096 14.8G c Win95 FAT32 (LBA)Disk /dev/mmcblk1: 7456 MB, 7818182656 bytes, 15269888 sectors238592 cylinders, 4 heads, 16 sectors/trackUnits: 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 LinuxDisk /dev/mmcblk1boot1: 4 MB, 4194304 bytes, 8192 sectors128 cylinders, 4 heads, 16 sectors/trackUnits: sectors of 1 * 512 = 512 bytesDisk /dev/mmcblk1boot1 doesn't contain a valid partition tableDisk /dev/mmcblk1boot0: 4 MB, 4194304 bytes, 8192 sectors128 cylinders, 4 heads, 16 sectors/trackUnits: sectors of 1 * 512 = 512 bytesDisk /dev/mmcblk1boot0 doesn't contain a valid partition tableDisk /dev/ramdisk: 2 MB, 2097152 bytes, 4096 sectors32 cylinders, 2 heads, 64 sectors/trackUnits: 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_MINOR3/* 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
# lsramdisk.ko# insmod ramdisk.koramdisk initramdisk major = 254ramdisk openramdisk release# ls -l /dev/ramdiskbrw-rw---- 1 root root 254, 0 Jan 1 00:51 /dev/ramdisk## rmmod ramdisk.koramdisk exit## ls -l /dev/ramdiskls: /dev/ramdisk: No such file or directory## insmod ramdisk.koramdisk initramdisk major = 254ramdisk openramdisk release## ls -l /dev/ramdiskbrw-rw---- 1 root root 254, 0 Jan 1 00:51 /dev/ramdisk## rmmod ramdisk.koramdisk exit## random: nonblocking pool is initialized# ls -l /dev/ramdiskls: /dev/ramdisk: No such file or directory#### insmod ramdisk.koramdisk initramdisk major = 254ramdisk openramdisk release## fdisk -lDisk /dev/mmcblk0: 15 GB, 15931539456 bytes, 31116288 sectors1936 cylinders, 255 heads, 63 sectors/trackUnits: sectors of 1 * 512 = 512 bytesDevice Boot StartCHS EndCHS Sramdisk opentartLBA EndLBA Sectors Siramdisk releaseze Id Type/dev/mmcblk0p1 0,1ramdisk open30,3 1023,254,63 8192 31116287 31108096 14.8G c Wiramdisk releasen95 FAT32 (LBA)Disk /dev/mmcblk1: 7456 MB, 7818182656 bytes, 15269888 sectors238592 cylinders, 4 heads, 16 sectors/trackUnits: 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 LinuxDisk /dev/mmcblk1boot1: 4 MB, 4194304 bytes, 8192 sectors128 cylinders, 4 heads, 16 sectors/trackUnits: sectors of 1 * 512 = 512 bytesDisk /dev/mmcblk1boot1 doesn't contain a valid partition tableDisk /dev/mmcblk1boot0: 4 MB, 4194304 bytes, 8192 sectors128 cylinders, 4 heads, 16 sectors/trackUnits: sectors of 1 * 512 = 512 bytesDisk /dev/mmcblk1boot0 doesn't contain a valid partition tableDisk /dev/ramdisk: 2 MB, 2097152 bytes, 4096 sectors32 cylinders, 2 heads, 64 sectors/trackUnits: sectors of 1 * 512 = 512 bytesDisk /dev/ramdisk doesn't contain a valid partition table#