调用class_create(),class_device_create()函数编译报错的解决方法

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在代码中加入class_create(),class_device_create()函数，编译时华丽丽得报了一大堆错误：

make -C /usr/src/linux-source-4.4.0   M=/home/ubuntu/Documents/first_drv   modules  make[1]: Entering directory '/usr/src/linux-source-4.4.0'  CC [M]  /home/ubuntu/Documents/first_drv/firstdrv.o/home/ubuntu/Documents/first_drv/firstdrv.c: In function ‘first_drv_init’:/home/ubuntu/Documents/first_drv/firstdrv.c:50:23: error: implicit declaration of function ‘class_device_create’ [-Werror=implicit-function-declaration]  firstdrv_class_dev = class_device_create(firstdrv_class, NULL, MKDEV(major, 0)                       ^/home/ubuntu/Documents/first_drv/firstdrv.c:50:21: warning: assignment makes pointer from integer without a cast [-Wint-conversion]  firstdrv_class_dev = class_device_create(firstdrv_class, NULL, MKDEV(major, 0)                     ^/home/ubuntu/Documents/first_drv/firstdrv.c: In function ‘first_drv_exit’:/home/ubuntu/Documents/first_drv/firstdrv.c:62:2: error: implicit declaration of function ‘class_device_unregister’ [-Werror=implicit-function-declaration]  class_device_unregister(firstdrv_class_dev);  ^cc1: some warnings being treated as errorsscripts/Makefile.build:264: recipe for target '/home/ubuntu/Documents/first_drv/firstdrv.o' failedmake[2]: *** [/home/ubuntu/Documents/first_drv/firstdrv.o] Error 1Makefile:1420: recipe for target '_module_/home/ubuntu/Documents/first_drv' failedmake[1]: *** [_module_/home/ubuntu/Documents/first_drv] Error 2make[1]: Leaving directory '/usr/src/linux-source-4.4.0'Makefile:19: recipe for target 'all' failedmake: *** [all] Error 2

网上搜索后发现是Linux内核版本不同的原因！早期的版本，使用的是上面说的两个函数，但是在2.6.29以后，使用的函数则变成了 class_create()和device_create()，并且要在声明中加入

#include <linux/device.h>

因为定义这些函数是在linux4.4.0/include/linux/device.h里面！
在first_drv_init（）和first_drv_exit（）函数中把class_device_create（）、
class_device_unregister（）函数修改为device_create（）和device_unregister（）后，error消失了，但还是有如下warning：

/home/ubuntu/Documents/first_drv/firstdrv.c:50:21: warning: assignment from incompatible pointer type [-Wincompatible-pointer-types]  firstdrv_class_dev = device_create(firstdrv_class, NULL, MKDEV(major, 0), NULL                     ^/home/ubuntu/Documents/first_drv/firstdrv.c: In function ‘first_drv_exit’:/home/ubuntu/Documents/first_drv/firstdrv.c:62:20: warning: passing argument 1 of ‘device_unregister’ from incompatible pointer type [-Wincompatible-pointer-types]  device_unregister(firstdrv_class_dev);                    ^In file included from /home/ubuntu/Documents/first_drv/firstdrv.c:6:0:include/linux/device.h:988:13: note: expected ‘struct device *’ but argument is of type ‘struct class_device *’ extern void device_unregister(struct device *dev);             ^  Building modules, stage 2.  MODPOST 1 modules  CC      /home/ubuntu/Documents/first_drv/firstdrv.mod.o  LD [M]  /home/ubuntu/Documents/first_drv/firstdrv.komake[1]: Leaving directory '/usr/src/linux-source-4.4.0'

原因是

static struct class_device *firstdrv_class_dev;

这个结构体指针变量的声明也要进行修改，改为

static struct device *firstdrv_class_dev;

完成上述修改后，编译ok啦

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