该函数用到的图1中的devlist数组定义如下:
static const struct memdev { const char *name; mode_t mode; const struct file_operations *fops; struct backing_dev_info *dev_info; } devlist[] = { [1] = { "mem", 0, &mem_fops, &directly_mappable_cdev_bdi }, #ifdef CONFIG_DEVKMEM [2] = { "kmem", 0, &kmem_fops, &directly_mappable_cdev_bdi }, #endif [3] = { "null", 0666, &null_fops, NULL }, #ifdef CONFIG_DEVPORT [4] = { "port", 0, &port_fops, NULL }, #endif [5] = { "zero", 0666, &zero_fops, &zero_bdi }, [7] = { "full", 0666, &full_fops, NULL }, [8] = { "random", 0666, &random_fops, NULL }, [9] = { "urandom", 0666, &urandom_fops, NULL }, [11] = { "kmsg", 0, &kmsg_fops, NULL }, #ifdef CONFIG_CRASH_DUMP [12] = { "oldmem", 0, &oldmem_fops, NULL }, #endif }; |
通过上面代码及图1可看出,memory_open实际上实现了一个分配器(根据次设备号区分各个设备,并且选择适当的file_operations),图2说明了打开内存设备时,文件操作是如何改变的。所涉及的函数逐渐反映了设备的具体特性。最初只知道用于打开设备的一般函数,然后由打开与内存相关设备文件的具体函数所替代。接下来根据选择的次设备号,进一步细化函数指针 ,为不同的次设备号最终选定函数指针。
图2:设备驱动程序函数指针的选择过程
本文转载自:http://blog.csdn.net/gqb666/article/details/8805179