英语词组
gen
disk
gendisk
之前讲解了字符驱动程序嵌入式linux高级驱动教程 pdf，这期开始讲解块设备驱动程序
字符设备与块设备的区别
字符设备驱动:
当应用层读写(read()/write())字符设备驱动时,是按字节/字符来读写数据的,期间没有任何缓存区,由于数据量小,不能随机读取数据,比如:按钮、LED、鼠标、键盘等
块设备:
块设备是i/o设备中的一类,当我们的应用层对该设备读写时,是按磁道大小来读写数据的,若读写的数据大于磁道的大小,都会须要缓存区,可以随机读写设备的任意位置处的数据嵌入式linux高级驱动教程 pdf，比如硬碟,U盘linux操作系统原理linux软件下载，SD卡。
总结：浅显来讲就是：块设备相当于是多个字符设备组成
块设备结构：重要的结构体定义
buffer_head
struct buffer_head {
unsigned long b_state; /* buffer state bitmap (see above) */
struct buffer_head *b_this_page;/* circular list of page's buffers */
struct page *b_page; /* the page this bh is mapped to */
sector_t b_blocknr; /* start block number */
size_t b_size; /* size of mapping */
char *b_data; /* pointer to data within the page */
struct block_device *b_bdev;
bh_end_io_t *b_end_io; /* I/O completion */
void *b_private; /* reserved for b_end_io */
struct list_head b_assoc_buffers; /* associated with another mapping */
struct address_space *b_assoc_map; /* mapping this buffer is
associated with */
atomic_t b_count; /* users using this buffer_head */
};bio
struct bio {
sector_t bi_sector; /* device address in 512 byte
sectors */
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
*/
unsigned short bi_vcnt; /* how many bio_vec's */
unsigned short bi_idx; /* current index into bvl_vec */
/* Number of segments in this BIO after
* physical address coalescing is performed.
*/
unsigned short bi_phys_segments;
/* Number of segments after physical and DMA remapping
* hardware coalescing is performed.
*/
unsigned short bi_hw_segments;
unsigned int bi_size; /* residual I/O count */
/*
* To keep track of the max hw size, we account for the
* sizes of the first and last virtually mergeable segments
* in this bio
*/
unsigned int bi_hw_front_size;
unsigned int bi_hw_back_size;
unsigned int bi_max_vecs; /* max bvl_vecs we can hold */
struct bio_vec *bi_io_vec; /* the actual vec list */
bio_end_io_t *bi_end_io;
atomic_t bi_cnt; /* pin count */
void *bi_private;
bio_destructor_t *bi_destructor; /* destructor */
};block_device
struct block_device {
dev_t bd_dev; /* not a kdev_t - it's a search key */
struct inode * bd_inode; /* will die */
int bd_openers;
struct mutex bd_mutex; /* open/close mutex */
struct semaphore bd_mount_sem;
struct list_head bd_inodes;
void * bd_holder;
int bd_holders;
#ifdef CONFIG_SYSFS
struct list_head bd_holder_list;
#endif
struct 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 list_head bd_list;
struct backing_dev_info *bd_inode_backing_dev_info;
/*
* 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;
};gendisk
struct gendisk {
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[32]; /* name of major driver */
struct hd_struct **part; /* [indexed by minor] */
int part_uevent_suppress;
struct block_device_operations *fops;
struct request_queue *queue;
void *private_data;
sector_t capacity;
int flags;
struct device *driverfs_dev;
struct kobject kobj;
struct kobject *holder_dir;
struct kobject *slave_dir;
struct timer_rand_state *random;
int policy;
atomic_t sync_io; /* RAID */
unsigned long stamp;
int in_flight;
#ifdef CONFIG_SMP
struct disk_stats *dkstats;
#else
struct disk_stats dkstats;
#endif
struct work_struct async_notify;
};block_device_operations
struct block_device_operations {
int (*open) (struct inode *, struct file *);
int (*release) (struct inode *, struct file *);
int (*ioctl) (struct inode *, struct file *, unsigned, unsigned long);
long (*unlocked_ioctl) (struct file *, unsigned, unsigned long);
long (*compat_ioctl) (struct file *, unsigned, unsigned long);
int (*direct_access) (struct block_device *, sector_t, unsigned long *);
int (*media_changed) (struct gendisk *);
int (*revalidate_disk) (struct gendisk *);
int (*getgeo)(struct block_device *, struct hd_geometry *);
struct module *owner;
};
buffer_head上面重要的成员结构体：
bio上面重要的成员结构体：
备注：typedefvoid(bh_end_io_t)(structbuffer_head*bh,intuptodate);
在块设备操作中重要的函数ll_rw_block
ll_rw_block：low-levelaccesstoblockdevices（块设备低级访问）
函数原型：voidll_rw_block(intrw,intnr,structbuffer_head*bhs[])
其调用过程：
1，ll_rw_block
2，struct buffer_head *bh = bhs[i];
3，submit_bh
4，struct bio *bio; bio = bio_alloc(GFP_NOIO, 1);
5，bio->bi_end_io = end_bio_bh_io_sync;
6，bio_get
7，submit_bio
8，bio_sectors
9，generic_make_request(bio);
10，__generic_make_request(bio);
11，q = bdev_get_queue(bio->bi_bdev);
12，return bdev->bd_disk->queue;
13，blk_partition_remap(bio);
14，ret = q->make_request_fn(q, bio);编撰一个最简单的块设备驱动程序
/* 参考:
* driversblockxd.c
* driversblockz2ram.c
*/
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
static struct gendisk *ramblock_disk;
static request_queue_t *ramblock_queue;
static int major;
static DEFINE_SPINLOCK(ramblock_lock);
#define RAMBLOCK_SIZE (1024*1024)
static unsigned char *ramblock_buf;
static int ramblock_getgeo(struct block_device *bdev, struct hd_geometry *geo)
{
/* 容量=heads*cylinders*sectors*512 */
geo->heads = 2;
geo->cylinders = 32;
geo->sectors = RAMBLOCK_SIZE/2/32/512;
return 0;
}
static struct block_device_operations ramblock_fops = {
.owner = THIS_MODULE,
.getgeo = ramblock_getgeo,
};
static void do_ramblock_request(request_queue_t * q)
{
static int r_cnt = 0;
static int w_cnt = 0;
struct request *req;
//printk("do_ramblock_request %dn", ++cnt);
while ((req = elv_next_request(q)) != NULL) {
/* 数据传输三要素: 源,目的,长度 */
/* 源/目的: */
unsigned long offset = req->sector * 512;
/* 目的/源: */
// req->buffer
/* 长度: */
unsigned long len = req->current_nr_sectors * 512;
if (rq_data_dir(req) == READ)
{
//printk("do_ramblock_request read %dn", ++r_cnt);
memcpy(req->buffer, ramblock_buf+offset, len);
}
else
{
//printk("do_ramblock_request write %dn", ++w_cnt);
memcpy(ramblock_buf+offset, req->buffer, len);
}
end_request(req, 1);
}
}
static int ramblock_init(void)
{
ramblock_disk = alloc_disk(16);
ramblock_queue = blk_init_queue(do_ramblock_request, &ramblock_lock);
ramblock_disk->queue = ramblock_queue;
major = register_blkdev(0, "ramblock");
ramblock_disk->major = major;
ramblock_disk->first_minor = 0;
sprintf(ramblock_disk->disk_name, "ramblock");
ramblock_disk->fops = &ramblock_fops;
set_capacity(ramblock_disk, RAMBLOCK_SIZE / 512);
ramblock_buf = kzalloc(RAMBLOCK_SIZE, GFP_KERNEL);
add_disk(ramblock_disk);
return 0;
}
static void ramblock_exit(void)
{
unregister_blkdev(major, "ramblock");
del_gendisk(ramblock_disk);
put_disk(ramblock_disk);
blk_cleanup_queue(ramblock_queue);
kfree(ramblock_buf);
}
module_init(ramblock_init);
module_exit(ramblock_exit);
MODULE_LICENSE("GPL");
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