Linux-Flash驱动(1)-块设备系统架构

本文主要是介绍Linux-Flash驱动(1)-块设备系统架构，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

1、块设备的体验

块设备快速体验：块设备是指只能以块为单位进行访问的设备，块大小一般是512个字节的整数倍。常见的块设备包括硬件，SD卡，光盘等。有同学会说，加入我需要通过硬盘访问1个字节的数据，难道无法访问吗？注意这里的512个字节是指对硬件设备的最小访问单元，对应用层访问数据的大小没有限制。

下面开始体验一下块设备：

将下面的代码保存后并编写模块的Makefile(参考前几课的代码)。

#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/init.h>#include <linux/sched.h>
#include <linux/kernel.h> /* printk() */
#include <linux/slab.h>   /* kmalloc() */
#include <linux/fs.h>   /* everything... */
#include <linux/errno.h> /* error codes */
#include <linux/timer.h>
#include <linux/types.h> /* size_t */
#include <linux/fcntl.h> /* O_ACCMODE */
#include <linux/hdreg.h> /* HDIO_GETGEO */
#include <linux/kdev_t.h>
#include <linux/vmalloc.h>
#include <linux/genhd.h>
#include <linux/blkdev.h>
#include <linux/buffer_head.h> /* invalidate_bdev */
#include <linux/bio.h>MODULE_LICENSE("Dual BSD/GPL");static int major = 0;static int sect_size = 512;static int nsectors = 1024; /*
* The internal representation of our device.
*/
struct blk_dev{int size;                        /* Device size in sectors */u8 *data;                        /* The data array */struct request_queue *queue;     /* The device request queue */struct gendisk *gd;              /* The gendisk structure */
};struct blk_dev *dev;/*
* Handle an I/O request, in sectors.
*/
static void blk_transfer(struct blk_dev *dev, unsigned long sector,unsigned long nsect, char *buffer, int write)
{
unsigned long offset = sector*sect_size;
unsigned long nbytes = nsect*sect_size;if ((offset + nbytes) > dev->size) {printk (KERN_NOTICE "Beyond-end write (%ld %ld)\n", offset, nbytes);return;
}
if (write)memcpy(dev->data + offset, buffer, nbytes);
elsememcpy(buffer, dev->data + offset, nbytes);
}/*
* The simple form of the request function.
*/
static void blk_request(struct request_queue *q)
{
struct request *req;req = blk_fetch_request(q);
while (req != NULL) {struct blk_dev *dev = req->rq_disk->private_data;blk_transfer(dev, blk_rq_pos(req), blk_rq_cur_sectors(req), req->buffer, rq_data_dir(req));if(!__blk_end_request_cur(req, 0)) {req = blk_fetch_request(q);}
}
}/*
* Transfer a single BIO.
*/
static int blk_xfer_bio(struct blk_dev *dev, struct bio *bio)
{
int i;
struct bio_vec *bvec;
sector_t sector = bio->bi_sector;/* Do each segment independently. */
bio_for_each_segment(bvec, bio, i) {char *buffer = __bio_kmap_atomic(bio, i, KM_USER0);blk_transfer(dev, sector, bio_cur_bytes(bio)>>9 /* in sectors */, buffer, bio_data_dir(bio) == WRITE);sector += bio_cur_bytes(bio)>>9; /* in sectors */__bio_kunmap_atomic(bio, KM_USER0);
}
return 0; /* Always "succeed" */
}/*
* Transfer a full request.
*/
static int blk_xfer_request(struct blk_dev *dev, struct request *req)
{
struct bio *bio;
int nsect = 0;__rq_for_each_bio(bio, req) {blk_xfer_bio(dev, bio);nsect += bio->bi_size/sect_size;
}
return nsect;
}/*
* The device operations structure.
*/
static struct block_device_operations blk_ops = {
.owner            = THIS_MODULE,
};/*
* Set up our internal device.
*/
static void setup_device()
{
/*
* Get some memory.
*/
dev->size = nsectors*sect_size;
dev->data = vmalloc(dev->size);
if (dev->data == NULL) {printk (KERN_NOTICE "vmalloc failure.\n");return;
}dev->queue = blk_init_queue(blk_request, NULL);if (dev->queue == NULL)goto out_vfree;blk_queue_logical_block_size(dev->queue, sect_size);
dev->queue->queuedata = dev;
/*
* And the gendisk structure.
*/
dev->gd = alloc_disk(1);
if (! dev->gd) {printk (KERN_NOTICE "alloc_disk failure\n");goto out_vfree;
}
dev->gd->major = major;
dev->gd->first_minor = 0;
dev->gd->fops = &blk_ops;
dev->gd->queue = dev->queue;
dev->gd->private_data = dev;
sprintf (dev->gd->disk_name, "simp_blk%d", 0);
set_capacity(dev->gd, nsectors*(sect_size/sect_size));
add_disk(dev->gd);
return;out_vfree:
if (dev->data)vfree(dev->data);
}static int __init blk_init(void)
{
/*
* Get registered.
*/
major = register_blkdev(major, "blk");
if (major <= 0) {printk(KERN_WARNING "blk: unable to get major number\n");return -EBUSY;
}dev = kmalloc(sizeof(struct blk_dev), GFP_KERNEL);
if (dev == NULL)goto out_unregister;setup_device();return 0;out_unregister:
unregister_blkdev(major, "sbd");
return -ENOMEM;
}static void blk_exit(void)
{if (dev->gd) {del_gendisk(dev->gd);put_disk(dev->gd);}if (dev->queue)blk_cleanup_queue(dev->queue);if (dev->data)vfree(dev->data);unregister_blkdev(major, "blk");
kfree(dev);
}module_init(blk_init);
module_exit(blk_exit);

编译并安装：

#make

#insmod simple-blk.ko

查看驱动文件：

#ls /dev/simp_blkdev0

可以看到这个设备是b开头的，代表block，块设备，然后把它初始化为ext3文件系统
#mkfs.ext3 /dev/simp_blk0

把快设备挂载到指定目录，比如新建一个/mnt/blk目录，然后挂载：
#mkdir –p /mnt/blk
#mount /dev/simp_blk0 /mnt/blk

对这个目录进行读写，在拷贝过程中会有警告，提示空间不足：
#cp /etc/init.d/* /mnt/blk

查看这个块设备，
#ls /mnt/blk

卸载这个设备
#umount /mnt/blk

再次查看，里面的文件应该没有了：
#ls /mnt/blk