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2013-01-29T15:00:19.483
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I think the story should starts from what happened when you type: <pre><code>mknod /dev/c83 c 8 3 </code></pre> it will call ext2_mknod("/dev", "c83", CHAR, DEV(8, 3)), most file systems implement mknod as a wrapper of init_special_inode: <pre><code>void init_special_inode(struct inode *inode, umode_t mode, dev_t rdev) { inode->i_mode = mode; if (S_ISCHR(mode)) { inode->i_fop = &def_chr_fops; inode->i_rdev = rdev; } else if (S_ISBLK(mode)) { inode->i_fop = &def_blk_fops; inode->i_rdev = rdev; } else if (S_ISFIFO(mode)) inode->i_fop = &def_fifo_fops; else if (S_ISSOCK(mode)) inode->i_fop = &bad_sock_fops; else printk(KERN_DEBUG "init_special_inode: bogus i_mode (%o)\n", mode); } </code></pre> when you finally call open("/dev/c83"), it will goes into function def_chr_fops.chrdev_open, which will replace the fops for file "/dev/c83" with the fops your registered in cdev_init(): <pre><code>int chrdev_open(struct inode * inode, struct file * filp) { struct cdev *p; ... p = inode->i_cdev; ... filp->f_op = fops_get(p->ops); ... if (filp->f_op->open) { lock_kernel(); ret = filp->f_op->open(inode,filp); unlock_kernel(); } ... return ret; } </code></pre> after that, every system call such as read/write/close goes directly to functions pointers registered in cdev_init()! so, for your first question: <ol> <li>yes, as you see in chrdev_open().</li> <li>yes, since the fops of devices is really same as the one registered in cdev_init</li> <li> plays a importance role in open(), since open() use pairs to find the correct device drivers. but after that, other file operations, such as read/write/close(), don't take part in again, everything goes through function pointers in fops resolved in open().</li> </ol>
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1. POThe role of major and minor numbers in device driver
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