1. 塊裝置概念:塊裝置是指隻能以塊為機關進行通路的裝置,塊的大小一般是512個位元組的整數倍。常見的塊裝置包括硬體,SD卡,CD光牒等。</span>
上邊是通過一個編寫好的塊裝置驅動,然後安裝塊裝置驅動以及一些相關操作來體會塊裝置驅動!(此處省略)
2. 塊裝置驅動的系統架構
2.1 系統架構---VFS
VFS是對各種具體檔案系統的一種封裝,使用者程式通路檔案提供統一的接口。
2.2 系統架構---Cache
當使用者發起檔案通路請求的時候,首先回到Disk Cache中尋址檔案是否被緩存了,如果在Cache,則直接從cache中讀取。如果資料不在緩存中,就必須要到具體的檔案系統中讀取資料了。
2.3 Mapping Layer
2.3.1 首先确定檔案系統的block size,然後計算所請求的 資料包含多少個block.
2.3.2 調用具體檔案系統的函數來通路檔案的inode結構,确定所請求的資料在磁盤上的位址。
2.4 Generic Block Layer
Linux核心把塊裝置看做是由若幹個扇區組成的資料空間,上層的讀寫請求在通用塊層被構造成一個或多個bio結構。
2.5 I/O Scheduler Layer I/O排程層負責采用某種算法(如:電梯排程算法)将I/O操作進行排序。
電梯排程算法的基本原則:如果電梯現在朝上運動,如果目前樓層的上方和下方都有請求,則先響應所有上方的請求,然後才向下響應下方的請求;如果電梯向下運動,則剛好相反。
2.6 塊裝置驅動
在塊系統架構的最底層,由塊裝置驅動根據排序好的請求,對硬體進行資料通路。
塊裝置驅動流程分析:
1.6 注冊塊裝置---add_disk
2. 實作讀寫請求函數
2.1 取出一個要處理的請求---blk_fetch_request
2.2 更具請求裡的資訊通路硬體,擷取資料
2.3 利用__blk_end_request_cur判讀請求隊列裡是否還有剩餘的請求要處理,如果有按照1、2來處理
一個最簡單的塊裝置驅動程式:
#include<linux/module.h>
#include<linux/init.h>
#include<linux/blkdev.h>
#include<linux/bio.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>
static int major = 0;
static int sect_size = 512;//定義每個扇區的大小為512位元組
static int nsectors = 1024;//扇區數目
struct blk_dev{
int size;
u8 *data;
struct request_queue *queue;
struct gendisk *gd;
};
struct blk_dev *dev;
static struct block_device_operations blk_ops = {
.owner = THIS_MODULE,
};
//static void blk_transfer(struct blk_dev *dev, unsigned long sector,unsigned long nsect, char *buffer, int write)
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 * sector;
if(write)//如果是寫操作 将使用者空間的資料寫到磁盤上去
memcpy(dev->data + offset, buffer, nbytes);
else
memcpy(buffer, dev->data + offset, nbytes);
}
static void blk_request(struct request_queue *q)
{
struct request *req;//儲存取出的請求
req = blk_fetch_request(q);//從請求隊列中取出一個請求
while(req != NULL)
{
//處理該請求
//操作的起始扇區 請求操作扇區的數目 資料讀出來放到哪裡, 或寫資料來自哪裡
blk_transfer(dev, blk_rq_pos(req), blk_rq_cur_sectors(req), req->buffer, rq_data_dir(req));
//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) )//判讀如果不是最後一個請求
req = blk_fetch_request(q);//再去取一個請求
}
}
void setup_device(void)
{
dev->size = nsectors * sect_size;
dev->data = vmalloc(dev->size);
dev->queue = blk_init_queue(blk_request, NULL);//初始化請求隊列
blk_queue_logical_block_size(dev->queue, sect_size);//設定扇區尺寸
dev->gd = alloc_disk(1);//配置設定塊裝置結構
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);//裝置名為simp_blk0
set_capacity(dev->gd, nsectors);//設定扇區數
add_disk(dev->gd);
}
int blk_init(void)
{
//兩個參數 第一個參數為0表示為動态配置設定裝置号 傳回主裝置号
major = register_blkdev(0, "blk");//注冊塊裝置驅動程式
if( major <= 0 )
{
printk("register blk dev fail!\n");
return -EBUSY;
}
dev = kmalloc(sizeof(struct blk_dev),GFP_KERNEL);
setup_device();
return 0;
}
void blk_exit(void)
{
del_gendisk(dev->gd);
blk_cleanup_queue(dev->queue);
vfree(dev->data);
unregister_blkdev(major, "blk");
kfree(dev);
}
module_init(blk_init);
module_exit(blk_exit);
編譯安裝 格式化成ext3的時候虛拟機直接重新開機了!原來驅動的BUG動不動就把系統搞挂!
這個是可以運作的:
#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);
else
memcpy(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);
makefile:
ifneq ($(KERNELRELEASE),)
obj-m := simple-blk.o
else
KDIR := /lib/modules/2.6.32-279.el6.i686/build
all:
make -C $(KDIR) M=$(PWD) modules
clean:
rm -f *.ko *.o *.mod.o *.mod.c *.symvers
endif
這個塊裝置驅動的測試上面也有步驟!重點是了解塊裝置驅動的大體流程!對塊裝置驅動又個大體印象!
下面來介紹一個和下面即将要出場的flash驅動相關的知識!
MTD
MTD裝置體驗:Flash在嵌入式系統中是必不可少,它是bootloader、linux核心和檔案系統的最佳載體。在linux核心中引入了MTD子系統為NOR FLASH和NAND FLASH裝置提供統一的接口,進而使得FLASH驅動的設計大為簡化。
塊裝置驅動系統架構:
先過一遍流程!額 ,徒手撸驅動代碼這難度還真不是一般大!後邊邊學邊提高吧!