一、概念:Poll是非阻塞IO----輪詢操作
非阻塞 I/O 的應(yīng)用程序常常使用 poll, select, 和 epoll 系統(tǒng)調(diào)用. poll, select 和 epoll 本質(zhì)上有相同的功能: 每個(gè)允許一個(gè)進(jìn)程來決定它是否可讀或者寫一個(gè)或多個(gè)文件而不阻塞.

Tip:select()和poll(),epoll查詢是否可對(duì)設(shè)備進(jìn)行無阻塞的訪問，這幾個(gè)系統(tǒng)調(diào)用最終又會(huì)引發(fā)設(shè)備驅(qū)動(dòng)中的poll()函數(shù)被執(zhí)行

PS:看到這感覺暈了,暫且不理會(huì)
二、使用場(chǎng)景:
它們常常用在必須使用多輸入輸出流的應(yīng)用程序(如調(diào)用read,write字符設(shè)備驅(qū)動(dòng)文件/dev/****)。因?yàn)檫@些調(diào)用也可阻塞進(jìn)程直到任何一個(gè)給定集合的文件描述符可用來讀或?qū)?
三、相關(guān)函數(shù)
1、內(nèi)核函數(shù)
內(nèi)核驅(qū)動(dòng)函數(shù)一)a)poll()函數(shù)原型:

unsigned int (*poll) (struct file *filp, poll_table *wait);

　　作用:調(diào)用poll_wait(),將可能引起設(shè)備文件狀態(tài)變化的等待隊(duì)列頭添加到poll_table.
返回值:返回是否能對(duì)設(shè)備進(jìn)行無阻塞讀寫訪問的掩碼

放回值mask常量及函數(shù)

常量 說明
POLLIN 普通或優(yōu)先級(jí)帶數(shù)據(jù)可讀
POLLRDNORM 普通數(shù)據(jù)可讀
POLLRDBAND 優(yōu)先級(jí)帶數(shù)據(jù)可讀
POLLPRI 高優(yōu)先級(jí)數(shù)據(jù)可讀
POLLOUT 普通數(shù)據(jù)可寫
POLLWRNORM 普通數(shù)據(jù)可寫
POLLWRBAND 優(yōu)先級(jí)帶數(shù)據(jù)可寫
POLLERR 發(fā)生錯(cuò)誤
POLLHUP 發(fā)生掛起
POLLNVAL 描述字不是一個(gè)打開的文件

內(nèi)核驅(qū)動(dòng)函數(shù)二)b)poll_wait()函數(shù)原型：

void poll_wait(struct file *filp, wait_queue_head_t *queue, poll_table *wait);

作用:將可能引起設(shè)備文件狀態(tài)變化的等待隊(duì)列頭添加到poll_table
2、應(yīng)用程序poll函數(shù)

int poll(struct pollfd *fds, nfds_t nfds, int timeout)

a)參數(shù)：
fds 指向 struct pollfd 數(shù)組
nfds 指定 pollfd 數(shù)組元素的個(gè)數(shù)，也就是要監(jiān)測(cè)幾個(gè) pollfd
timeout 時(shí)間參數(shù)，單位ms，1000ms=1s
Tip:fds可以是很多個(gè)文件(如網(wǎng)卡，按鍵)，poll可以論尋fds[n]
b)結(jié)構(gòu)體pollfd
struct pollfd {
int fd;
short events;
short revents;
};

3、總結(jié):從應(yīng)用程序的調(diào)用來看，并不需要理會(huì)內(nèi)核函數(shù)中的參數(shù)poll_table *wait是什么,只需要調(diào)用poll_wait()

四、使用模板
模板一)a)內(nèi)核程序模板

static DECLARE_WAIT_QUEUE_HEAD(waitq);//定義結(jié)構(gòu)體名稱為waitq
poll(struct file *file, poll_table *wait){//返回mask
unsigned int mask = 0;
poll_wait(file, &waitq, wait);
if(...)//可讀
｛
mask |= POLLIN | POLLRDNORM; //標(biāo)識(shí)數(shù)據(jù)可獲得
｝
if(...)//可寫
｛
mask |= POLLOUT | POLLRDNORM; //標(biāo)識(shí)數(shù)據(jù)可寫入
｝
return mask;
}

模板二）b)測(cè)試程序模板

struct pollfd fds[n];
fds[0].fd = fd;
fds[0].events = POLLIN;
poll(fds, n, 5000);

c)再次理解下面幾句
fds 指向 struct pollfd 數(shù)組
nfds 指定 pollfd 數(shù)組元素的個(gè)數(shù)，也就是要監(jiān)測(cè)幾個(gè) pollfd
timeout 時(shí)間參數(shù)，單位ms，1000ms=1s
Tip:fds可以是很多個(gè)文件(如網(wǎng)卡，按鍵)，poll可以論尋fds[n]

實(shí)例一)五、案例jz2440中斷非阻塞驅(qū)動(dòng)實(shí)例

1、 非阻塞內(nèi)核按鍵驅(qū)動(dòng)。

//“irq_drv”,"irq_","irq"
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
static DECLARE_WAIT_QUEUE_HEAD(button_waitq);//定義結(jié)構(gòu)體名稱為button_waitq
static struct class *irq_class;
static struct class_device *irq_class_dev;
static int ev_press = 0;
static unsigned char key_val;
struct pin_desc{
unsigned int pin;
unsigned int key_val;
};
struct pin_desc pins_desc[3] = {
{S3C2410_GPF0, 0x01},
{S3C2410_GPF2, 0x02},
{S3C2410_GPG3, 0x03},
};
static irqreturn_t irq_handle(int irq, void *dev__id){
//printk("irq = %dn", irq);
int pinval;
struct pin_desc *pindesc = (struct pin_desc *)dev__id;
pinval = s3c2410_gpio_getpin(pindesc->pin);
if(!pinval){//按下
key_val = pindesc->key_val;
}else{//松開
key_val = 0x80 | pindesc->key_val;
}
ev_press = 1;
wake_up_interruptible(&button_waitq);
return IRQ_RETVAL(IRQ_HANDLED);//warn:返回IRQ_HANDLED
}
static unsigned irq_drv_poll(struct file *file, poll_table *wait)
{
unsigned int mask = 0;
poll_wait(file, &button_waitq, wait); // 不會(huì)立即休眠
if (ev_press)
mask |= POLLIN | POLLRDNORM;
return mask;
}
static int irq_drv_open(struct inode *inode, struct file *file)
{
printk("irq_dev readn");
// request_irq(unsigned int irq, irq_handler_t handler, unsigned long irqflags, const char * devname, void * dev_id); dev_id隨意
request_irq(IRQ_EINT0, irq_handle, IRQ_TYPE_EDGE_BOTH, "s2", &pins_desc[0]);
request_irq(IRQ_EINT2, irq_handle, IRQ_TYPE_EDGE_BOTH, "s3", &pins_desc[1]);
request_irq(IRQ_EINT11, irq_handle, IRQ_TYPE_EDGE_BOTH, "s4", &pins_desc[2]);
return 0;
}
static ssize_t irq_drv_read (struct file *file, char __user *buf, size_t count, loff_t *ppos){
if(count != 1)return -EINVAL;
wait_event_interruptible(button_waitq, ev_press);//ev_press標(biāo)志(if!(ev_press)),那么一直休眠
copy_to_user(buf, &key_val, 1);//一個(gè) char 0xff
ev_press = 0;
return 1;//warn :return the size of val
}
static ssize_t irq_drv_write(struct file *file, const char __user *buf, size_t count, loff_t * ppos)
{
printk("irq_dev writen");
return 0;
}
static ssize_t irq_drv_release(struct inode *inode, struct file *file){
free_irq(IRQ_EINT0, &pins_desc[0]);
free_irq(IRQ_EINT2, &pins_desc[1]);
free_irq(IRQ_EINT11, &pins_desc[2]);
return 0;
}
static struct file_operations irq_drv_fops = {
.owner = THIS_MODULE, /* 這是一個(gè)宏，推向編譯模塊時(shí)自動(dòng)創(chuàng)建的__this_module變量 */
.open = irq_drv_open,
.write = irq_drv_write,
.read = irq_drv_read,
.release = irq_drv_release,
.poll = irq_drv_poll,
};
int major;
static int irq_drv_init(void)
{
major = register_chrdev(0, "irq_drv", &irq_drv_fops); // 注冊(cè), 告訴內(nèi)核
if (major < 0) {
printk(" cant register major numbern");
return major;
}
irq_class = class_create(THIS_MODULE, "irq_drv");
if (IS_ERR(irq_class))
return PTR_ERR(irq_class);
irq_class_dev = class_device_create(irq_class, NULL, MKDEV(major, 0), NULL, "irq"); /* /dev/xyz */
if (IS_ERR(irq_class_dev))
return PTR_ERR(irq_class_dev);
return 0;
}
static void irq_drv_exit(void)
{
unregister_chrdev(major, "irq_drv"); // 卸載
class_device_unregister(irq_class_dev);
class_destroy(irq_class);
}
module_init(irq_drv_init);
module_exit(irq_drv_exit);
MODULE_LICENSE("GPL");

2、測(cè)試應(yīng)用程序

#include
#include
#include
#include
#include
#include
/* irq
*/
int main(int argc, char **argv)
{
int fd;
unsigned char key_val;
int cnt = 0;
int ret;
struct pollfd fds[1];
fd = open("/dev/irq", O_RDWR);
if (fd < 0)
{
printf("cant open!n");
exit(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, &key_val, 1);
printf("key_Vals = 0x%xn", key_val);
}
}
return 0;
}
Makefile
#myirq.bin
objs := $(patsubst %c, %o, $(shell ls *.c))
myarmgcc := /workspacearm/armlinuxgcc2626/bin/arm-linux-gcc
myirq.bin:$(objs)
$(myarmgcc) -o $@ $^
cp *.bin /opt/fsmini/
%.o:%.c
$(myarmgcc) -c -o $@ $<
clean:
rm -f *.bin *.o

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