On Mon, Feb 23, 2009 at 3:11 AM, Kevin Wilson <wkevils@xxxxxxxxx> wrote:
> Hello,
>
> Following is a simple kernel module of 40 lines which only registers a
> misc device. I insmod the module and it is ok; the return value of
> misc_register() is 0.
> ls -al /dev/mymodule
> gives:
> crw-rw---- 1 root root 10, 300 22-02-09 20:58 /dev/mymodule
> which is ok.
> However, when I try, from a user space program, to open the device,
> by calling open("/dev/mymodule", O_RDONLY) , I get an error.
> The error I get when running the user space program is:
> open: No such device or address
>
> I would appreciate if anyone has an idea why is it so. The kernel
> module and the user space
> program are below.
>
> kernel module:
> #define MY_MINOR 300
>
> static long my_ioctl(struct file *filp, unsigned int cmd, unsigned long data)
> {
> return 0;
> }
>
> struct file_operations mymodule_fops =
> {
> .owner = THIS_MODULE,
> .unlocked_ioctl = my_ioctl,
> .compat_ioctl = my_ioctl,
> };
it seemed your file_operations may be correct (without the traditional
open()) interface, as I noticed that drivers/char/toshiba.c is also
declared thus:
static const struct file_operations tosh_fops = {
.owner = THIS_MODULE,
.ioctl = tosh_ioctl,
};
But then it also puzzled me, because ioctl() in user space required a
open file descriptor as the first parameter, which is derived from
open() (as specified from "man ioctl"). so then how is the open()
from userspace passed down to kernel?
>
> static struct miscdevice my_dev = {
> MY_MINOR,
> "mymodule",
> &mymodule_fops,
> };
>
> static int __init mymodule_init(void)
> {
> int ret;
> mymodule_fops.owner = THIS_MODULE;
> ret = misc_register(&my_dev);
> printk("ret = %d\n",ret);
> if (ret)
> return -1;
> return 0;
> }
>
> static void __exit mymodule_exit(void)
> {
> misc_deregister(&my_dev);
> }
> module_init(mymodule_init)
> module_exit(mymodule_exit)
> -----------------
>
>
> The user space program:
>
> int main()
> {
> int fd;
>
> fd = open("/dev/mymodule", O_RDONLY);
> if (fd == -1) {
> perror("open");
> exit(1);
> }
> printf("open succeeded\n");
>
> }
>
putting aside my open doubts....i think the problem u have is got to
do with udev not setup properly:
search in google:
http://www.google.com/search?q=%22open%3A+No+such+device+or+address%22+udev&btnG=Google+Search
or more specifically (which started with your error):
http://www.ip-phone-forum.de/showthread.php?p=695114
I certainly don't understand any German....but from "You made my
day!", i know it is happy ending.
--
Regards,
Peter Teoh
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