内核：linux -2.6.22.6
从代码的角度来看，poll机制是通过应用程序调用poll() 函数,poll()函数的使用方法可以通过man poll进行查看，可仿照最终程序中进行改写，这里不做重复说明。配合驱动函数中相对应的drv_poll() 函数配套使用的。函数执行的入口当然是应用程序中的poll()函数，接着进入内核中的sys_poll() 函数，poll机制的函数在路经：linux/fs/select.c下，原代码如下：
我要评论739 asmlinkage long sys_poll(struct pollfd __user *ufds, unsigned int nfds,
740 long timeout_msecs)
741 {
742 s64 timeout_jiffies;
743
744 if (timeout_msecs > 0) {
745 #if HZ > 1000
746 /* We can only overflow if HZ > 1000 */
747 if (timeout_msecs / 1000 > (s64)0x7fffffffffffffffULL / (s64)HZ)
748 timeout_jiffies = -1;
749 else
750 #endif
751 timeout_jiffies = msecs_to_jiffies(timeout_msecs);
752 } else {
753 /* Infinite (< 0) or no (0) timeout */
754 timeout_jiffies = timeout_msecs;
755 }
756
757 return do_sys_poll(ufds, nfds, &timeout_jiffies);
758 }可以看出除了return中使用的do_sys_poll()函数，其他全都是初始化时间。所以进一步对**do_sys_poll()**函数进行分析，部分原代码如下：
653 int do_sys_poll(struct pollfd __user *ufds, unsigned int nfds, s64 *timeout){
....
670 poll_initwait(&table); // 初始化table
......
709 fdcount = do_poll(nfds, head, &table, timeout);710 // 真正执行poll函数
......
737 }首先初始化table通过阅读代码可以看出table主要设置的是将table->qproc设置成__pollwait模式。
另一步骤进入do_poll函数，do_poll()函数原代码如下：
582 static int do_poll(unsigned int nfds, struct poll_list *list,
583 struct poll_wqueues *wait, s64 *timeout)
584 {
585 int count = 0;
586 poll_table* pt = &wait->pt;
587
588 /* Optimise the no-wait case */
589 if (!(*timeout))
590 pt = NULL;
591
592 for (;;) {
593 struct poll_list *walk;
594 long __timeout;
595
596 set_current_state(TASK_INTERRUPTIBLE);
597 for (walk = list; walk != NULL; walk = walk->next) {
598 struct pollfd * pfd, * pfd_end;
599
600 pfd = walk->entries;
601 pfd_end = pfd + walk->len;
602 for (; pfd != pfd_end; pfd++) {
603 /*
604 * Fish for events. If we found one, record it
605 * and kill the poll_table, so we don't
606 * needlessly register any other waiters after
607 * this. They'll get immediately deregistered
608 * when we break out and return.
609 */
610 if (do_pollfd(pfd, pt)) {
611 count++;
612 pt = NULL;
613 }
614 }
615 }
616 /*
617 * All waiters have already been registered, so don't provide
618 * a poll_table to them on the next loop iteration.
619 */
620 pt = NULL;
621 if (count || !*timeout || signal_pending(current))
622 break;
623 count = wait->error;
624 if (count)
625 break;
626
627 if (*timeout < 0) {
628 /* Wait indefinitely */
629 __timeout = MAX_SCHEDULE_TIMEOUT;
630 } else if (unlikely(*timeout >= (s64)MAX_SCHEDULE_TIMEOUT-1)) {
631 /*
632 * Wait for longer than MAX_SCHEDULE_TIMEOUT. Do it in
633 * a loop
634 */
635 __timeout = MAX_SCHEDULE_TIMEOUT - 1;
636 *timeout -= __timeout;
637 } else {
638 __timeout = *timeout;
639 *timeout = 0;
640 }
641
642 __timeout = schedule_timeout(__timeout);
643 if (*timeout >= 0)
644 *timeout += __timeout;
645 }
646 __set_current_state(TASK_RUNNING);
647 return count;
648 }通过分析将其简写为：
for(;;){
if(do_pollfd(pfd, pt)){ // do_pollfd调用我们的drv_poll函数，以及挂载队列，此函数在接下去分析
count++; //如果由我们的drv_poll函数返回值为1，时间发生
pt = NULL;
}
if(count || *timeout || signal_pending(current)) //计数count不为0 或者 超时 或者 有信号在等待处理
break; //不休眠
_timeout = schedule_timeout(__timeout); // 休眠
}接着分析do_pollfd函数，函数原代码如下所示：
555 static inline unsigned int do_pollfd(struct pollfd *pollfd, poll_table *pwait)
556 {
557 unsigned int mask;
558 int fd;
559
560 mask = 0;
561 fd = pollfd->fd;
562 if (fd >= 0) {
563 int fput_needed;
564 struct file * file;
565
566 file = fget_light(fd, &fput_needed);
567 mask = POLLNVAL;
568 if (file != NULL) {
569 mask = DEFAULT_POLLMASK;
570 if (file->f_op && file->f_op->poll)
571 mask = file->f_op->poll(file, pwait); //执行驱动函数中的drv_poll函数
572 /* Mask out unneeded events. */
573 mask &= pollfd->events | POLLERR | POLLHUP;
574 fput_light(file, fput_needed);
575 }
576 }
577 pollfd->revents = mask;
578
579 return mask; //返回mask
580 }由do_poll函数中的分析可以大致看出来do_pollfd函数的作用就是在判断某一条件是否满足，来使count++。所以进一步就涉及到了drv_poll的返回值mask。
接着编写驱动函数中的drv_poll函数
unsigned int botton_drv_poll(struct file *fd, struct poll_table_struct *wait)
{
unsigned int mask = 0;
poll_wait(fd, &button_waitq, wait); // 不会立即休眠 只是加入等待队列
if (ev_press) //若发生中断 返回值mask = 1
mask |= POLLIN | POLLRDNORM;
return mask; //若不发生中断返回值 mask = 0
}其中主要函数为poll_wait，这个函数主要干的事情是：把当前进程添加到wait参数指定的等待列表(button_waitq)中。需要注意的是这个函数是不会引起阻塞的，真正引起休眠的是do_poll中的schedule_timeout。
所以该函数主要完成的是判断是否发生中断。若发生中断返回1，未发生中断的话返回0。
结合sys_poll()函数可以看出来，若返回值为1则发生中断唤醒，若返回值为0则为超时唤醒。
总的来说，poll加上之前的中断函数，休眠的条件有两个：
但是值得注意的是，进入read的条件为：由于中断被唤醒，所以进入休眠的条件不得到满足（ev_press =1)，所以总的来说只有一个中断起作用，相对应的唤醒有两个方式：
这两种中断对应于两个返回值，以及两种处理方式。
对于整个poll处理过程可以由一下的伪代码表示：
app: poll(fds, 1, 5000)；
kernal： sys_poll()
do_sys_poll(..., timeout_jiffies)
poll_initwait(&table)
init_poll_funcptr(&pwq->pt, __pollwait)
table->qproc = __pollwait // 初始化
do_poll(nfds, head, &table, timeout)
for(;;){
for(输入文件数组){ //如果任意一个满足条件count则不为0
if(do_pollfd(pfd, pt)){ dopollfd()>>> mask = file->f_op->poll(file, pwait)
>>>__pollwait(file, &button_waitq, p)
count++; //若驱动函数drv_poll的返回值为1条件发生
pt = NULL;
}
}
if(count || !*timeout || signal_pending(current))
break; // 如果发生中断或者时间超时则 不休眠
__timeout = schedule_timeout(__timeout); //休眠
}
因此基于poll函数功能，设计整个程序大体的流程如下图所示：
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/delay.h>
#include <asm/uaccess.h>
#include <asm/irq.h>
#include <asm/io.h>
#include <asm/arch/regs-gpio.h>
#include <asm/hardware.h>
#include <linux/device.h>
#include <linux/kdev_t.h>
#include <linux/compiler.h>
#include <linux/err.h>
#include <linux/irqreturn.h>
//#include <asm/arch-s3c2410/irqs.h>
#include <linux/irq.h>
#include <asm/arch-s3c2410/regs-gpio.h>
#include <linux/poll.h>
#define DEV_NAME "button_drv" // device name
static struct class *buttondrv_class;
static struct class_device *buttondrv_class_dev;
static DECLARE_WAIT_QUEUE_HEAD(button_waitq);
/* 中断事件标志, 中断服务程序将它置1，third_drv_read将它清0 */
static volatile int ev_press = 0;
/* 键值: 按下时, 0x01, 0x02, 0x03, 0x04 */
/* 键值: 松开时, 0x81, 0x82, 0x83, 0x84 */
static unsigned char key_val;
volatile unsigned long *gpfcon = NULL;
volatile unsigned long *gpfdat = NULL;
volatile unsigned long *gpgcon = NULL;
volatile unsigned long *gpgdat = NULL;
struct pin_desc{
volatile unsigned long *key_Register;
int key_pin;
int key_num;
};
struct pin_desc pins_desc[4] = {
{0x01, 0, 1},
{0x02, 2, 2},
{0x03, 3, 3},
{0x04, 11, 4},
};
static irqreturn_t button_irq(int irq, void *dev_id)
{
struct pin_desc *pindesc = (struct pin_desc *)dev_id;
key_val = ((*(pindesc -> key_Register)) & (1<<(pindesc -> key_pin))) ? 0 : 1;
if(key_val)
{
// printk("%d", pindesc -> key_num);
}
printk("%d ",key_val);
printk("%d\n",pindesc->key_num);
ev_press = 1; /* 表示中断发生了 */
wake_up_interruptible(&button_waitq); /* 唤醒休眠的进程 */
return IRQ_HANDLED;
}
static int button_drv_open(struct inode *inode, struct file *file)
{
pins_desc[0].key_Register = gpfdat;
pins_desc[1].key_Register = gpfdat;
pins_desc[2].key_Register = gpgdat;
pins_desc[3].key_Register = gpgdat;
request_irq(IRQ_EINT0, button_irq, IRQT_BOTHEDGE, "S2", &pins_desc[0]);
request_irq(IRQ_EINT2, button_irq, IRQT_BOTHEDGE, "S3", &pins_desc[1]);
request_irq(IRQ_EINT11, button_irq, IRQT_BOTHEDGE, "S4", &pins_desc[2]);
request_irq(IRQ_EINT19, button_irq, IRQT_BOTHEDGE, "S5", &pins_desc[3]);
return 0;
}
ssize_t button_drv_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
{
if(size == -1)
return -EINVAL;
/* 如果没有按键动作, 休眠 */
wait_event_interruptible(button_waitq, ev_press);
/* 如果有按键动作, 返回键值 */
copy_to_user(buf, &key_val, 1);
ev_press = 0;
return 1;
}
static int EINTkey_close(struct inode *inode, struct file *file)
{
// FREE IRQ
free_irq(IRQ_EINT0, &pins_desc[0]);
free_irq(IRQ_EINT2, &pins_desc[1]);
free_irq(IRQ_EINT11, &pins_desc[2]);
free_irq(IRQ_EINT19, &pins_desc[3]);
return 0;
}
unsigned int botton_drv_poll(struct file *fd, struct poll_table_struct *wait)
{
unsigned int mask = 0;
poll_wait(fd, &button_waitq, wait); // 不会立即休眠
if (ev_press)
mask |= POLLIN | POLLRDNORM;
return mask;
}
static struct file_operations button_drv_fops = {
.owner = THIS_MODULE, /* 这是一个宏，推向编译模块时自动创建的__this_module变量 */
.open = button_drv_open,
.read = button_drv_read,
.release = EINTkey_close,
.poll = botton_drv_poll,
};
int major;
static int button_drv_init(void)
{
major = register_chrdev(0, DEV_NAME, &button_drv_fops); // 注册, 告诉内核// register chrdev. to major (major, "drv name", file operations);
buttondrv_class = class_create(THIS_MODULE, "buttondrv");
if(IS_ERR(buttondrv_class))
{
printk( "ERROR creat key class");
}
buttondrv_class_dev = class_device_create(buttondrv_class, NULL, MKDEV(major, 0), NULL, "buttons"); /* /dev/xyz */
if(buttondrv_class_dev == NULL)
{
printk("ERROR creat dev");
}
gpfcon = (volatile unsigned long *)ioremap(0x56000050, 16); //remap button GPFCPN
gpfdat = gpfcon + 1; //remap button GPFDAT
gpgcon = (volatile unsigned long *)ioremap(0x56000060, 16); //remap button GPGCPN
gpgdat = gpgcon + 1; //remap button GPGDAT
return 0;
}
static void button_drv_exit(void)
{
unregister_chrdev(major, DEV_NAME); // 卸载
class_device_unregister(buttondrv_class_dev);
class_destroy(buttondrv_class);
iounmap(gpgcon);
iounmap(gpfcon); // unmap virtual address
}
module_init(button_drv_init); //When install drv, system will find init function
module_exit(button_drv_exit); // Uinstall drv
MODULE_LICENSE("GPL");#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <poll.h>
// button_drv
int main(int argc, char **argv)
{
int ret; // poll use
int fd; //
unsigned char button_val;
fd = open("/dev/buttons", O_RDWR);
if (fd < 0)
printf("can't open!\n");
if(argc != 1) {
printf("error parterner\n");
printf("%s\n",argv[0]);
return 0;
}
struct pollfd fds[1];
fds[0].fd = fd;
fds[0].events = POLLIN;
while(1){
ret = poll(fds, 1, 5000);
if(ret == 0)
printf("time out \n");
else
read(fd, button_val, sizeof(button_val));
}
return 0;
}本文地址：https://blog.csdn.net/qq_41668705/article/details/107155989
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