字符设备常用代码段

---头文件

#include <linux/module.h>
#include <linux/types.h>
#include <linux/fs.h>
#include <linux/error.h>
#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/cdev.h>
#include <asm/io.h>
#include <asm/system.h>
#include <asm/uaccess.h>

---设备号的申请

static int mem_major = MEMDEV_MAJOR;

int result;
dev_t devno = MKDEV(mem_major, 0);

if (mem_major)
    result = register_chrdev_region(devno, 1, "chrdev");
else
{
    //该处的chrdev的名字显示在/proc/devices里面，跟/dev中的设备节点木有关系，他们通过主设备号关联
    result = alloc_chrdev_region(&devno, 0, 1, "chrdev");
    mem_major = MAJOR(devno);
    printk("Major-->%d\n", mem_major);
}

if (result < 0)
    return result;

---利用private

/* 对于存在多个次设备的情况下filp->private_data就能发挥特殊作用 */
int mem_open(struct inode *inode, struct file *filp)
{
    struct mem_dev *dev;
    int num = MINOR(inode->i_rdev);//或者num = iminor(inode);
    if (num >= MEMDEV_NR_DEVS)
        return -ENODEV;
    dev = &mem_devp[num];

    filp->private_data = dev;
}

---设备的初始化、注册和注销

struct cdev cdev;
cdev_init(&cdev, &mem_fops);
cdev.owner = THIS_MODULE;
//cdev.ops = &mem_fops;
//或者用下面的代码
struct cdev *cdev = cdev_alloc();
cdev->ops = &mem_fops;

cdev_add(&cdev, MKDEV(mem_major, 0), MEMDEV_NR_DEVS);

cdev_del(&cdev);
unregister_chrdev_region(MKDEV(mem_major, 0), MEMDEV_NR_DEVS);

---创建、注销设备文件

//手动创建设备节点
mknod filename type major minor
//自动生成设备节点
//2.6.12
#ifdef CONFIG_DEVFS_FS
devfs_mk_cdev(devno, S_IFCHR|S_IRUGO|S_IWUSR, "globalmem");
#endif
//2.6.32
struct class *my_class;
my_class = class_create(THIS_MODULE, "my_class");
if (IS_ERR(my_class))
    return -1;
device_create(my_class, NULL, MKDEV(globalmem_major, 0), NULL, "globalmemdev");
//自动注销设备节点
device_destroy(my_class, MKDEV(globalmem_major, 0));
class_destroy(my_class);

--poll模板

static unsigned int xxx_poll(struct file *filp, poll_tabel *wait)
{
    unsigned int mask = 0;
    struct xxx_dev *dev = filp->private_data;

    poll_wait(filp, &dev->r_wait, wait);
    poll_wait(filp, &dev->w_wait, wait);

    if (...)
    {
        mask |= POLLIN | POLLRDNORM;
    }

    if (xxx)
    {
        mask |= POLLOUT | POLLWRNORM;
    }

    ...
    return mask;
}

--应用层select
需要注意的是：读写集都要添加(否则，可能会有问题)，根据需要选择while语句里面的if分支。

fd_set rfds, wfds;
while(1)
{
    FD_ZERO(&rfds);
    FD_ZERO(&wfds);
    FD_SET(fd, &rfds);
    FD_SET(fd, &wfds);

    select(fd + 1, &rfds, &wfds, NULL, NULL);
    if (FD_ISSET(fd, &rfds))
    {
        if (size = read(fd, buf_r, 10) < 10)
        {
            xxx;
        }
        else
            xxx;
    }

    if (FD_ISSET(fd, &wfds))
    {

    }
}

---tasklet和工作队列

//tasklet
void xxx_do_tasklet(unsigned long);
DECLARE_TASKLET(xxx_tasklet, xxx_do_tasklet, 0);

/*中断底半部*/
void xxx_do_tasklet(unsigned long)
{
}

/*中断顶半部*/
irqreturn_t xx_interrupt(int irq, void *dev_id, struct pt_regs *regs)
{
    ...
    tasklet_schedule(&xxx_tasklet);
    ...
}

//工作队列
struct work_struct xxx_wq;
void xxx_do_work(unsigned long);

/*中断底半部*/
void xxx_do_work(unsigned long)
{
}

/*中断顶半部*/
irqreturn_t xx_interrupt(int irq, void *dev_id, struct pt_regs *regs)
{
    ...
    schedule_work(&xxx_wq);
    ...
}

int __init xxx_init(void)
{
...
    INIT_WORK(&xxx_wq, (void(*)(void*))xxx_do_work, NULL);
...
}