块设备驱动（Linux kernel 4.9.x）

主要结构

gendisk结构体：表示一个独立的磁盘设备(或分区)

1.1 定义如下：
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;...};1.2 一组操作gendisk函数/* 分配gendisk */struct gendisk *alloc_disk(int minors);   /* 添加gendisk */void device_add_disk(struct device *parent, struct gendisk *disk); void add_disk(struct gendisk *disk);/* 设置gendisk容量 */void set_capacity(struct gendisk *disk, sector_t size);  /* 释放gendisk */void del_gendisk(struct gendisk *gp);

request、request_queue和bio结构

2.1 request结构体
struct request {struct list_head queuelist;union {struct call_single_data csd;u64 fifo_time;};struct request_queue *q;struct blk_mq_ctx *mq_ctx;int cpu;unsigned cmd_type;unsigned int cmd_flags;       /* op and common flags */req_flags_t rq_flags;unsigned long atomic_flags;/* 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;......struct gendisk *rq_disk;struct hd_struct *part;unsigned long start_time;......unsigned 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;
};2.2 request_queue结构体
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;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;init_rq_fn     *init_rq_fn;exit_rq_fn      *exit_rq_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;.../** 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;....../** 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 work_struct  timeout_work;struct list_head   timeout_list;struct list_head   icq_list;......struct 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*/struct blk_flush_queue  *fq;struct list_head    requeue_list;spinlock_t     requeue_lock;struct delayed_work    requeue_work;struct mutex       sysfs_lock;int          bypass_depth;atomic_t       mq_freeze_depth;......struct rcu_head       rcu_head;wait_queue_head_t  mq_freeze_wq;struct percpu_ref  q_usage_counter;struct list_head    all_q_node;struct blk_mq_tag_set    *tag_set;struct list_head   tag_set_list;struct bio_set     *bio_split;bool         mq_sysfs_init_done;size_t           cmd_size;void           *rq_alloc_data;
};2.3 bio结构体
struct bio {struct bio      *bi_next;   /* request queue link */struct block_device *bi_bdev;int            bi_error;unsigned int       bi_opf;     /* bottom bits req flags,* top bits REQ_OP. Use* accessors.*/unsigned short     bi_flags;   /* status, command, etc */unsigned short        bi_ioprio;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;......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];
};2.4 bio_vec结构体
struct bio_vec {struct page *bv_page;unsigned int   bv_len;unsigned int bv_offset;
};

block_device_operations结构体：类似于字符设备中的file_operations结构体

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 *, bool);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 **, pfn_t *,long);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;const struct pr_ops *pr_ops;
};其中int (*getgeo)(struct block_device *, struct hd_geometry *);是用来获取驱动器的信息，hd_geometry结构体中包含磁头、扇面、柱面等信息。

驱动的注册/注销、加载/卸载函数

注册与注销

int register_blkdev(unsigned int major, const char *name);
int unregister_blkdev(unsigned int major, const char *name);

加载
1）注册块设备;
2）
分配gendisk、初始化(设置)gendisk；
设置gendisk容量；
初始化请求队列、设置队列；
3）添加gendisk。
NOTE: 2)项内容并无前后顺序。
卸载
1）释放gendisk（若有对gendisk的引用，也要释放）；
2）移除请求队列；
3）注销块设备;
NOTE: 以上三步并无前后顺序。
实例：以drivers/block/z2ram.c为例(省略返回值判断)

static int __init z2_init(void)
{int ret;...if (register_blkdev(Z2RAM_MAJOR, DEVICE_NAME))          /* 注册块设备 */goto err;ret = -ENOMEM;z2ram_gendisk = alloc_disk(1);                          /* 分配gendisk */...z2_queue = blk_init_queue(do_z2_request, &z2ram_lock);   /* 初始化请求队列 */...z2ram_gendisk->major = Z2RAM_MAJOR;z2ram_gendisk->first_minor = 0;z2ram_gendisk->fops = &z2_fops;sprintf(z2ram_gendisk->disk_name, "z2ram");z2ram_gendisk->queue = z2_queue;add_disk(z2ram_gendisk);                               /* 添加gendisk */blk_register_region(MKDEV(Z2RAM_MAJOR, 0), Z2MINOR_COUNT, THIS_MODULE,z2_find, NULL, NULL);return 0;...
}static void __exit z2_exit(void)
{int i, j;blk_unregister_region(MKDEV(Z2RAM_MAJOR, 0), Z2MINOR_COUNT);unregister_blkdev(Z2RAM_MAJOR, DEVICE_NAME);      /* 注销块设备 */del_gendisk(z2ram_gendisk);                          /* 释放gendisk */put_disk(z2ram_gendisk);                         /* 释放对gendisk的引用 */blk_cleanup_queue(z2_queue);                     /* 移除请求队列 */......return;
}

块设备的open、release、ioctl等函数

该部分指的是：前面介绍的block_device_operations结构体下指向的函数。

块设备的I/O请求处理

使用请求队列：对于机械的磁盘设备，有助于提高系统的性能。
不使用请求队列：如存储卡、RAM盘等完全可真正随机访问的设备，无法从请求队列逻辑获益的块设备。

实例

Ramdisk：利用内存(RAM)模拟磁盘，数据实际存储在内存中，以块设备的方式访问内存。
/* Ram backed block device driver（drivers/block/brd.c） —不使用请求队列的块设备 */

static struct brd_device *brd_alloc(int i)
{struct brd_device *brd;struct gendisk *disk;brd = kzalloc(sizeof(*brd), GFP_KERNEL);......brd->brd_queue = blk_alloc_queue(GFP_KERNEL);               /* 分配“请求队列” */...blk_queue_make_request(brd->brd_queue, brd_make_request);   /* 绑定“制造请求”函数 */blk_queue_max_hw_sectors(brd->brd_queue, 1024);blk_queue_bounce_limit(brd->brd_queue, BLK_BOUNCE_ANY);blk_queue_physical_block_size(brd->brd_queue, PAGE_SIZE);brd->brd_queue->limits.discard_granularity = PAGE_SIZE;blk_queue_max_discard_sectors(brd->brd_queue, UINT_MAX);brd->brd_queue->limits.discard_zeroes_data = 1;queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, brd->brd_queue);...disk = brd->brd_disk = alloc_disk(max_part);...disk->major     = RAMDISK_MAJOR;disk->first_minor   = i * max_part;disk->fops       = &brd_fops;disk->private_data  = brd;disk->queue       = brd->brd_queue;disk->flags     = GENHD_FL_EXT_DEVT;sprintf(disk->disk_name, "ram%d", i);set_capacity(disk, rd_size * 2);return brd;...
}
/* 加载函数 */
static int __init brd_init(void)
{struct brd_device *brd, *next;int i;......if (register_blkdev(RAMDISK_MAJOR, "ramdisk"))return -EIO;...for (i = 0; i < rd_nr; i++) {brd = brd_alloc(i);...list_add_tail(&brd->brd_list, &brd_devices);}/* point of no return */list_for_each_entry(brd, &brd_devices, brd_list)add_disk(brd->brd_disk);blk_register_region(MKDEV(RAMDISK_MAJOR, 0), 1UL << MINORBITS,THIS_MODULE, brd_probe, NULL, NULL);pr_info("brd: module loaded\n");return 0;
}

IDE(Integrated Drive Electronics)：集成驱动器电路。原名ATA接口，本意为将硬盘控制器与盘体集成在一起的硬盘驱动器。
NOTE：关于IDE的代码均在内核目录drivers/ide/下。

小结

块设备和字符设备的I/O操作区别
1）块设备只能以块为单位进行输入/输出；而字符设备则以字节为单位。
2）块设备对于I/O请求有缓存区，可以选择以什么顺序进行响应；而字符设备则无需缓冲区，直接读写。
—块设备的I/O操作中贯穿“请求”，会排队和组合。
3）块设备可以随机访问（对于磁盘，组织顺序访问有助于提高访问效率）；而字符设备只能顺序读写。
块设备驱动程序
1）驱动的任务—处理请求。I/O调度算法解决请求的排队和整合。
2）驱动的核心—请求处理函数、“制造请求”函数。
3）驱动虽包含block_device_operations结构体(类似于字符设备中的file_operations结构体)，但不再包含读写一类的成员函数。仅包含打开、释放及I/O 控制等与具体读写无关的函数。

Linux驱动开发---块设备驱动相关推荐

Linux驱动开发|块设备驱动
块设备驱动块设备驱动是 Linux 三大驱动类型之一,块设备驱动比字符设备驱动复杂得多,不同类型的存储设备又对应不同的驱动子系统,下面介绍块设备驱动框架及使用一.块设备介绍块设备是针对存储设备的 ...
linux中流设备_[快速上手Linux设备驱动]之块设备驱动流程详解一
[快速上手Linux设备驱动]之块设备驱动流程详解一 walfred已经在[快速上手Linux设备驱动]之我看字符设备驱动一文中详细讲解了linux下字符设备驱动,并紧接着用四篇文章描述了Linux ...
＜Linux开发＞--驱动开发-- 字符设备驱动（3）过程详细记录
<Linux开发>–驱动开发-- 字符设备驱动(3) 过程详细记录驱动开发是建立再系统之上的,前面作者也记录了系统移植的过程记录,如果有兴趣,可进入博主的主页查看相关文章,这里就不添加链 ...
Linux 设备驱动开发 —— platform设备驱动应用实例解析
前面我们已经学习了platform设备的理论知识Linux 设备驱动开发 -- platform 设备驱动 ,下面将通过一个实例来深入我们的学习. 一.platform 驱动的工作过程 platfor ...
STM32MP157驱动开发——蜂鸣器设备驱动
STM32MP157驱动开发--蜂鸣器设备驱动 0.相关知识一.驱动程序开发 1.设备树修改 2.启动程序编写 3.测试程序编写二.编译及运行测试 0.相关知识蜂鸣器常用于计算机.打印机.报 ...
STM32MP157驱动开发——platform设备驱动(中)
STM32MP157驱动开发--platform设备驱动(中) 0.前言一.platform设备模块--设备信息解析二.platform驱动模块--加载设备三.测试App 四.编译及运行相关文 ...
STM32MP157驱动开发——USB设备驱动
STM32MP157驱动开发--USB设备驱动一.简介 1.电气属性 2.USB OTG 3.STM32MP1 USB 接口简介 4.Type-C 电气属性二.USB HOST 驱动开发 1.US ...
Linux 设备驱动开发 —— platform 设备驱动
一.platform总线.设备与驱动在Linux 2.6 的设备驱动模型中,关心总线.设备和驱动3个实体,总线将设备和驱动绑定.在系统每注册一个设备的时候,会寻找与之匹配的驱动:相反 ...
十六、Linux驱动之块设备驱动
1. 基本概念块设备是Linux三大设备之一,其驱动模型主要针对磁盘,Flash等存储类设备,块设备(blockdevice)是一种具有一定结构的随机存取设备,对这种设备的读写是按块(所以叫块设备) ...

Linux驱动开发---块设备驱动

块设备驱动（Linux kernel 4.9.x）

主要结构

驱动的注册/注销、加载/卸载函数

块设备的open、release、ioctl等函数

块设备的I/O请求处理

实例

小结

Linux驱动开发---块设备驱动相关推荐

最新文章

热门文章