how to create device node for dynamically allocated major number

appas · 09-30-2004, 07:52 AM

Hi all,
I am writing a char driver for which the major number is not statically assigned.
i pass zero as argument for 'register_chrdev' so that major number is dynamically generated.
But now I do not know how to create the device node since i the major number is not known.
Could someone help me how to get the major number to create device node.
I did not find any information in /proc/devices after loading the driver.

Hko · 09-30-2004, 09:12 AM

I know next-to-nothing about kernel-programming, but I doubt it's actually possible to have dynamic major devie numbers.

AFAIK the new devfs is made to overcome this limitation, but I assume it does not have anything to do with major number etc. like with the "old" device-driver system.

Or am I wrong about this?

appas · 10-01-2004, 03:53 AM

Hi Hko,
It is certainly possible to dynamically allocate a major number while registering the driver. This can be done by passing zero as the argument for 'register_chr_dev' function which was confirmed in my driver by printing the return value of 'register_chr_dev'.
I do not know anything about devfs and i will look into that.

Hko · 10-01-2004, 04:15 AM

Quote:

Originally posted by appas
It is certainly possible to dynamically allocate a major number while registering the driver. This can be done by passing zero as the argument for 'register_chr_dev' function which was confirmed in my driver by printing the return value of 'register_chr_dev'.

OK. Learned something new here. Thanks.
I didn't know, and I didn't expect it, because how would you know which major number to use for the /dev node? Which is exactly your question...

appas · 10-01-2004, 09:09 AM

Hi all,
First of all, sorry for the misleading statement i used in the thread starting

Quote:

" I did not find any information in /proc/devices after loading the driver."

After loading the module, /proc/devices contains information about the major number and device.
Now i can get the major number for the device and then execute "mknod" to create the device.

kadissie · 11-01-2004, 09:37 AM

According to the Linux LKM programming guide you should use the mknod system call. Try "man 2 mknod" for more info.

Don't forget to delete the file when you cleanup!

R.