open系统调用在内核中的流程分析

转自：

http://blog.sina.com.cn/s/blog_523491650100cdd7.html

open系统调用在内核中的流程分析

真是蛮复杂的，我分三步走，力求讲得比较清楚。 以字符设备为例，相对于块设备要简单些。 基于2.6.26的内核 Understand the Linux Kernel 3rd里面其实都讲到了，所以想再深入的话，可以去参考那本书。 一）驱动注册open函数都干了些什么？ register_chrdev -> cdev_add ->  kobj_map file: fs/char_dev.c int register_chrdev(unsigned int major, const char *name,                    const struct file_operations *fops) {        struct char_device_struct *cd;        struct cdev *cdev;        char *s;        int err = -ENOMEM;        cd = __register_chrdev_region(major, 0, 256, name);        if (IS_ERR(cd))                return PTR_ERR(cd);        cdev = cdev_alloc();        if (!cdev)                goto out2;        cdev->owner = fops->owner;        cdev->ops =fops;      // 注意，在后面的 chrdev_open会从cdev再得到 fops ... } file: fs/char_dev.c int cdev_add(struct cdev *p, dev_t dev, unsigned count) {        p->dev = dev;        p->count = count;        return kobj_map(cdev_map, dev, count, NULL, exact_match,exact_lock, p); } file: fs/char_dev.c static struct kobject *exact_match(dev_t dev, int *part, void*data) {        struct cdev *p = data;        return &p->kobj; } file: drivers/base/map.c int kobj_map(struct kobj_map *domain, dev_t dev, unsigned longrange,             struct module *module, kobj_probe_t *probe,             int (*lock)(dev_t, void *), void *data) {        unsigned n = MAJOR(dev + range - 1) - MAJOR(dev) + 1;        unsigned index = MAJOR(dev);        unsigned i;        struct probe *p;        if (n > 255)                n = 255;        p = kmalloc(sizeof(struct probe) * n, GFP_KERNEL);