块设备驱动学习笔记(二)——实例模板
vmem_disk驱动
此驱动大体分成三个部分：加载、卸载模块，block_device_operations结构体中各方法的实现，I/O请求处理函数
前两部分相对容易理解，现帖出最后一部分。
static void vmem_disk_transfer(struct vmem_disk_dev *dev,unsigned long sector,unsigned long nsector,char *buffer,int write)
{
unsigned long offset=sector*KERNEL_SECTOR_SIZE;
unsigned long nbytes=nsect*KERNEL_SECTOR_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);
}
//以上是实际操作块设备的代码，但不知为何采用memcpy（）这个函数。
static void vmem_disk_request(struct request_queue *q)
{
struct request *req;
while((req=elv_next_request(q))!=NULL){
struct vmem_disk_dev *dev=req->rq_disk->private_data;
if(!blk_fs_request(req)){
printk(KERN_NOTICE “Skip non-fd request\n”);
end_request(req,0);
continue;
}
vmem_disk_transfer(dev,req->sector,req->current_nr_sectors,req->buffer,rq_data_dir(req));
end_request(req,1);
}
}
/*以上函数为request_mode=RM_SIMPLE时，请求队列绑定的处理函数。处理函数调用的vmem_disk_transfer所用到的参数，皆由request提供。elv_next_request()函数是从队列中取出一个要处理的请求*/
static int vmem_disk_xfer_bio(struct vmem_disk_dev *dev,struct bio *bio)
{
int i;
struct bio_vec *bec;
sector_t sector=bio->bi_sector;
bio_for_each_segment(bvec,bio,i){
char *buffer = __bio_kmap_atomic(bio,i,KM_USER0);
vmem_disk_transfer(dev,sector,bio_cur_sectors(bio),buffer,bio_data_dir(bio)==WRITE);
sector += bio_cur_sectors(bio);
__bio_kunmap_atomic(bio,KM_USER0);
}
return 0;
}
/*以上函数由“制造请求函数”调用，从实际效果看相当于拥有了一个实际request产生的结果。因为调用绑定“制造请求”函数的初衷是不使用请求。而请求是由上层bio经块层转化而来的。所有就只能使用bio来确定物理结构相关的操作地址。__bio_kmap_atomic()函数返回一个bio第i个缓冲区的虚拟地址，至于为什么char 类型，真是有点费解。接下来调用的vmem_disk_transfer所用到的参数皆由bio结构来提供*/
static int mem_disk_xfer_request(struct vmem_disk_dev *dev,struct request *req)
{
struct req_iterator iter;
int nsect=0;
struct bio_vec *bvec;
rq_for_each_segment(bvec,req,iter){
char *buffer=_bio_kmap_atomic(iter.bio,iter.i,KM_USER0);
sector_t sector =iter.bio->bi_sector;
vmem_disk_transfer(dev,sector,bio_cur_sectors(iter.bio),buffer,bio_data_dir(iter.bio)==WRITE);
sector +=bio_cur_sectors(iter.bio);
__bio_kunmap_atomic(iter.bio,KM_USER0);
nsec +=iter.bio->bi_size/KERNEL_SECTOR_SIZE;
}
return nsect;
}
/*以上函数处理过程和vmem_disk_xfer_bio的处理过程很相似。只是多引入了一个结构struct req_iterator, 然后在vmem_disk_transfer的各参数前加上一个iter的前缀。此函数是在request_mode=RM_FULL时调用的，至于为什么多加一个结构体就功能强大一些，待解决。*/
static void vmem_disk_full_request(struct request_queue *q)
{
struct request *req;
int sectors_xferred;
struct vmem_disk_dev *dev =q->queuedata;
while((req=elv_next_request(q))!=NULL){
if(!blk_fs_request(req){
printk(KERN “skip non-fs request\n”);
end_request(req,0);
continue;
}
sectors_sferred=vmem_disk_xfer_request(dev,req);
end_request(req,1):
}
}
static int vmem_disk_make_request(struct request_queue *q,struct bio *bio)
{
struct vmem_disk_dev *dev=q->queuedata;
int status;
status=vmem_disk_xfer_bio(dev,bio);
bio_endio(bio,status);
return 0;
}