Hi,
my previous post with open method seems to be wrong.
On Sun, Feb 22, 2009 at 8:11 PM, 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
Minor number couldn't be bigger like 255. I think this cause a problem
with opening.
I change to e.g. : 149 and works fine without open method.
Please check.
I think also udev should check max. values for minor and major numbers.
I don't use udev but I set entry in device table and then get error when run
makedevs with minor 300. Seems makedevs works properly.
>
> 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,
> };
>
> 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");
>
> }
>
> Regards,
> Kevin
>
> --
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>
>
good luck,
Marek
--
as simple as primitive as possible
----------------------------------------------
Marek Beliško - open-nandra
Ruská Nová Ves 219
08005 Prešov
Slovakia
http://open-nandra.com
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