驅(qū)動之路-高級字符設備驅(qū)動程序

高級字符設備驅(qū)動在簡單字符驅(qū)動的基礎(chǔ)上添加ioctl方法、阻塞非阻塞讀寫、poll方法、和自動創(chuàng)建設備文件的功能。

一、重要知識點

1.ioctl

ioctl命令：使用4個字段定義一個ioctl命令，包括

type: 幻數(shù)，一般使用一個字符定義，在內(nèi)核中唯一。

number: 序數(shù)。

direction: 數(shù)據(jù)傳輸方向，當不涉及數(shù)據(jù)傳輸時，此字段無效。

size: 所涉及用戶數(shù)據(jù)的大小，當不涉及數(shù)據(jù)傳輸時，此字段無效。

_IOC_NONE

_IOC_READ

_IOC_WRITE

“方向”字段的可能值。“讀”和“寫”是不同的位，可以用“OR”在一起指定讀寫。

_IOC(dir, type, size)

_IO(type,nr)

_IOR(type, nr, size)

_IOW(type, nr, size)

用于生產(chǎn)ioctl命令的宏

_IOC_DIR(cmd)

_IOC_TYPE(cmd)

_IOC_NR(cmd)

_IOC_SIZE(cmd)

用于解碼ioctl命令的宏

intaccess_ok(int type, const void *addr, unsigned long size)

這個函數(shù)驗證指向用戶空間的指針是否可用，如果允許訪問，access_ok返回非0值。

int put_user(datum, ptr)

int get_user(local, ptr)

int __put_user(datum, ptr)

int __get_user(local, ptr)

用于向（或從）用戶空間保存（或獲取）單個數(shù)據(jù)項的宏。傳送的字節(jié)數(shù)目由sizeof(*ptr)決定。前兩個要先調(diào)用access_ok,后兩個（__put_user和__get_user）則假設access_ok已經(jīng)被調(diào)用過了。

2.阻塞型I/O

typedef struct {/*…..*/} wait_queue_head_t

void init_waitqueue_head(wait_queue_head_t*queue)

DECLARE_WAIT_QUEUE_HEAD(queue)

預先定義的Linux內(nèi)核等待隊列類型。wait_queue_head_t類型必須顯示地初始化，初始化方法可以在運行時調(diào)用init_waitqueue_head,或在編譯時DECLARE_WAIT_QUEUE_HEAD。

void wait_event((wait_queue_head_t q, intcondition)

int wait_event_interruptible(wait_queue_head_tq, int condition)

int wait_event_timeout(wait_queue_head_t q,int condition, int time)

int wait_event_interruptible_timeout(wait_queue_head_tq, int condition, int time)

使進程在指定的隊列上休眠，直到給定的condition值為真。

void wake_up(struct wait_queue **q)

void wake_up_interruptible(structwait_queue **q)

這些函數(shù)喚醒休眠在隊列q上的進程。_interruptible形式的函數(shù)只能喚醒可中斷的進程。在實踐中約定做法是在使用wait_event時用wake_up,而在使用wait_event_interruptible時使用wake_up_interruptible。

3.poll方法

poll方法分兩步處理，第一步調(diào)用poll_wait指定等待隊列，第二步返回是否可操作的掩碼。

POLLIN表示設備可讀的掩碼，POLLRDORM表示數(shù)據(jù)可讀的掩碼。POLLOUT表示設備可寫的掩碼，POLLWRNORM表示數(shù)據(jù)可讀的掩碼。一般同時返回POLLIN和POLLRDORM或者POLLOUT和POLLWRNORM。

4.select系統(tǒng)調(diào)用

原型為intselect(int mafdp1, fd_set *restrict readfds, fd_set *restrict writefds, fd_set*restrict exceptfds, struct timeval *restrict tvptr)

返回值：就緒的描述符數(shù)，若超時則返回0，若出錯則返回-1

void FD_ISSET(int fd, fd_set *fdset)

void FD_CLR(int fd, fd_set *fdset)

void FD_SET(int fd, fd_set *fdset)

void FD_ZERO(fd_set *fdset)

調(diào)用FD_ZERO將一個指定的fd_set變量的所有位設置為0。調(diào)用FD_SET設置一個fd_set變量指定位。調(diào)用FD_CLR則將一指定位清除。最后，調(diào)用FD_ISSET測試一指定位是否設置。

5.自動創(chuàng)建設備文件

struct class *class_create(struct module*owner, const char *name)

struct device *device_create(struct class*class, struct device *parent, dev_t devt, const char *fmt, ...)??????????

通過這兩個函數(shù)可以專門用來創(chuàng)建一個字符設備文件節(jié)點，class_create 第一個參數(shù)指定所有者，第二參數(shù)指定類得名字。class_device_create第一個參數(shù)指定第一個參數(shù)指定所要創(chuàng)建的設備所從屬的類，第二個參數(shù)是這個設備的父設備，如果沒有就指定為NULL，第三個參數(shù)是設備號，第四個參數(shù)是設備名稱。

二、驅(qū)動代碼

#include???

#define?MEMDEV_MAJOR?251??

#define?MEMDEV_NUM?2??

#define?MEMDEV_SIZE?1024??

//定義設備IOCTL命令??

#define?MEMDEV_IOC_MAGIC?'k'??

#define?MEMDEV_IOC_NR?2??

#define?MEMDEV_IOC_PRINT_IO(MEMDEV_IOC_MAGIC,?0)??

#define?MEMDEV_IOC_RD_IOR(MEMDEV_IOC_MAGIC,?1,?int)??

#define?MEMDEV_IOC_WT_IOW(MEMDEV_IOC_MAGIC,?2,?char)??

struct?mem_dev??

{??

unsignedint?size;??

char*data;??

structsemaphore?sem;??

wait_queue_head_t??inque;??

};??

static?int?mem_major?=?MEMDEV_MAJOR;??

struct?cdev?mem_cdev;??

struct?mem_dev?*mem_devp;??

bool?havedata?=?false;??

static?int?mem_open(struct?inode?*inode,struct?file?*filp)??

{??

structmem_dev?*dev;??

unsignedint?num;??

printk("mem_open.\n");??

num=?MINOR(inode->i_rdev);//獲得次設備號??

if(num>?(MEMDEV_NUM?-1))??????????//檢查次設備號有效性??

return-ENODEV;??

dev=?&mem_devp[num];??

filp->private_data=?dev;?//將設備結(jié)構(gòu)保存為私有數(shù)據(jù)??

return0;??

}??

static?int?mem_release(struct?inode?*inode,struct?file?*filp)??

{??

printk("mem_release.\n");??

return0;??

}??

static?ssize_t?mem_read(struct?file?*filp,char?__user?*buf,?size_t?size,?loff_t?*ppos)??

{??

intret?=?0;??

structmem_dev?*dev;??

unsignedlong?p;??

unsignedlong?count;??

printk("mem_read.\n");??

dev=?filp->private_data;//獲得設備結(jié)構(gòu)??

count=?size;??

p=?*ppos;??

//檢查偏移量和數(shù)據(jù)大小的有效性??

if(p>?MEMDEV_SIZE)??

return0;??

if(count>?(MEMDEV_SIZE-p))??

count=?MEMDEV_SIZE?-?p;??

if(down_interruptible(&dev->sem))//鎖定互斥信號量??

return-ERESTARTSYS;??

while(!havedata)??

{??

up(&dev->sem);??

if(filp->f_flags&?O_NONBLOCK)??

return-EAGAIN;??

printk("readyto?go?sleep");??

if(wait_event_interruptible(dev->inque,havedata))//等待數(shù)據(jù)??

return-ERESTARTSYS;??

if(down_interruptible(&dev->sem))??

return-ERESTARTSYS;??

}??

//讀取數(shù)據(jù)到用戶空間??

if(copy_to_user(buf,dev->data+p,?count)){??

ret=?-EFAULT;??

printk("copyfrom?user?failed\n");??

}??

else{??

*ppos+=?count;??

ret=?count;??

printk("read%ld?bytes?from?dev\n",?count);??

havedata=?false;//數(shù)據(jù)已經(jīng)讀出??

}??

up(&dev->sem);//解鎖互斥信號量??

returnret;??

}??

static?ssize_t?mem_write(struct?file?*filp,const?char?__user?*buf,?size_t?size,?loff_t?*ppos)//注意：第二個參數(shù)和read方法不同??

{??

intret?=?0;??

structmem_dev?*dev;??

unsignedlong?p;??

unsignedlong?count;??

printk("mem_write.\n");??

dev=?filp->private_data;??

count=?size;??

p=?*ppos;??

if(p>?MEMDEV_SIZE)??

return0;??

if(count>?(MEMDEV_SIZE-p))??

count=?MEMDEV_SIZE?-?p;??

if(down_interruptible(&dev->sem))//鎖定互斥信號量??

return-ERESTARTSYS;??

if(copy_from_user(dev->data+p,buf,?count)){??

ret=?-EFAULT;??

printk("copyfrom?user?failed\n");??

}??

else{??

*ppos+=?count;??

ret=?count;??

printk("write%ld?bytes?to?dev\n",?count);??

havedata=?true;??

wake_up_interruptible(&dev->inque);//喚醒等待數(shù)據(jù)的隊列??

}??

up(&dev->sem);//解鎖互斥信號量??

returnret;??

}??

static?loff_t?mem_llseek(struct?file?*filp,loff_t?offset,?int?whence)??

{??

intnewpos;??

printk("mem_llseek.\n");??

switch(whence)??

{??

case0://從文件頭開始??

newpos=?offset;??

break;??

case1://從文件當前位置開始??

newpos=?filp->f_pos?+?offset;??

break;??

case2://從文件末尾開始??

newpos=?MEMDEV_SIZE?-?1?+?offset;??

break;??

default:??

return-EINVAL;??

}??

if((newpos<0)||?(newpos>(MEMDEV_SIZE?-?1)))??

return-EINVAL;??

filp->f_pos=?newpos;??

returnnewpos;??

}??

static?int?mem_ioctl(struct?inode?*inode,struct?file?*filp,?unsigned?int?cmd,?unsigned?long?arg)??

{??

interr?=?0,?ret?=?0;??

intioarg?=?0;??

charrdarg?=?'0';??

//參數(shù)檢查??

if(_IOC_TYPE(cmd)!=?MEMDEV_IOC_MAGIC)//參數(shù)類型檢查??

return-ENOTTY;??

if(_IOC_NR(cmd)>?MEMDEV_IOC_NR)//參數(shù)命令號檢查??

return-ENOTTY;??

//用戶空間指針有效性檢查??

if(_IOC_DIR(cmd)&?_IOC_READ)??

err=?!access_ok(VERIFY_WRITE,?(void?__user?*)arg,?_IOC_SIZE(cmd));??

elseif(_IOC_DIR(cmd)?&?_IOC_WRITE)??

err=?!access_ok(VERIFY_WRITE,?(void?__user?*)arg,?_IOC_SIZE(cmd));??

if(err)??

return-ENOTTY;??

//根據(jù)命令執(zhí)行操作??

switch(cmd)??

{??

case?MEMDEV_IOC_PRINT:??

printk("memdevioctl?print?excuting...\n");??

break;??

caseMEMDEV_IOC_RD:??

ioarg=?1024;??

ret??=?__put_user(ioarg,?(int?*)arg);//用戶空間向內(nèi)核空間獲得數(shù)據(jù)??

printk("memdevioctl?read?excuting...?\n");??

break;??

caseMEMDEV_IOC_WT:??

ret=?__get_user(rdarg,?(char?*)arg);//用戶空間向內(nèi)核空間傳輸數(shù)據(jù)??

printk("memdevioctl?write?excuting...?arg:%c\n",?rdarg);??

break;??

default:??

return-ENOTTY;??

}??

returnret;??

}??

static?unsigned?int?mem_poll(struct?file*filp,?poll_table?*wait)??

{??

structmem_dev?*dev;??

unsignedint?mask?=?0;??

dev=?filp->private_data;??

if(down_interruptible(&dev->sem))//鎖定互斥信號量??

return-ERESTARTSYS;??

poll_wait(filp,&dev->inque,?wait);??

if(havedata)??

mask|=?POLLIN?|?POLLRDNORM;//返回可讀掩碼??

up(&dev->sem);//釋放信號量??

returnmask;??

}??

static?const?struct?file_operationsmem_fops?=?{??

.owner=?THIS_MODULE,??

.open=?mem_open,??

.write=?mem_write,??

.read=?mem_read,??

.release=?mem_release,??

.llseek=?mem_llseek,??

.ioctl=?mem_ioctl,??

.poll=?mem_poll,??

};??

static?int?__init?memdev_init(void)??

{??

intresult;??

interr;??

inti;??

structclass?*memdev_class;??

//申請設備號??

dev_tdevno?=?MKDEV(mem_major,?0);??

if(mem_major)??

result=?register_chrdev_region(devno,?MEMDEV_NUM,?"memdev");//注意靜態(tài)申請的dev_t參數(shù)和動態(tài)dev_t參數(shù)的區(qū)別??

else{??????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????//靜態(tài)直接傳變量，動態(tài)傳變量指針??

result=?alloc_chrdev_region(&devno,?0,?MEMDEV_NUM,?"memdev");??

mem_major=?MAJOR(devno);??

}??

if(result

printk("can'tget?major?devno:%d\n",?mem_major);??

returnresult;??

}??

//注冊設備驅(qū)動??

cdev_init(&mem_cdev,&mem_fops);??

mem_cdev.owner=?THIS_MODULE;??

err=?cdev_add(&mem_cdev,?MKDEV(mem_major,?0),?MEMDEV_NUM);//如果有N個設備就要添加N個設備號??

if(err)??

printk("add?cdev?faild,err?is%d\n",?err);??

//分配設備內(nèi)存??

mem_devp=?kmalloc(MEMDEV_NUM*(sizeof(struct?mem_dev)),?GFP_KERNEL);??

if(!mem_devp){??

result?=?-?ENOMEM;??

goto?fail_malloc;??

}??

memset(mem_devp,0,?MEMDEV_NUM*(sizeof(struct?mem_dev)));??

for(i=0;i

mem_devp[i].size=?MEMDEV_SIZE;??

mem_devp[i].data=?kmalloc(MEMDEV_SIZE,?GFP_KERNEL);??

memset(mem_devp[i].data,0,?MEMDEV_SIZE);??

init_MUTEX(&mem_devp[i].sem);//初始化互斥鎖??

//初始化等待隊列??

init_waitqueue_head(&mem_devp[i].inque);??

}??

//自動創(chuàng)建設備文件??

memdev_class=?class_create(THIS_MODULE,?"memdev_driver");??

device_create(memdev_class,NULL,?MKDEV(mem_major,?0),?NULL,?"memdev0");??

returnresult;??

fail_malloc:??

unregister_chrdev_region(MKDEV(mem_major,0),?MEMDEV_NUM);??

returnresult;??

}??

static?void?memdev_exit(void)??

{??

cdev_del(&mem_cdev);??

unregister_chrdev_region(MKDEV(mem_major,0),?MEMDEV_NUM);//注意釋放的設備號個數(shù)一定要和申請的設備號個數(shù)保存一致??

//否則會導致設備號資源流失??

printk("memdev_exit\n");??

}??

module_init(memdev_init);??

module_exit(memdev_exit);??

MODULE_AUTHOR("Y-Kee");??

MODULE_LICENSE("GPL");??

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