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So you can make a device file with a command, mknod or mknod, the name of the file, then either a c or a b for character or block, and then a number which will be known as the major device number and another number known as the minor.
Description. The mknod command makes a directory entry and corresponding i-node for a special file. The first parameter is the name of the entry device. Select a name that is descriptive of the device.
In order to prevent kernel modules loading during boot, the module name must be added to a configuration file for the "modprobe" utility. This file must reside in /etc/modprobe. d . Ensure the module is not configured to get loaded in either /etc/modprobe.
The classic way to register a char device driver is with: int register_chrdev(unsigned int major, const char *name, struct file_operations *fops); Here, major is the major number of interest, name is the name of the driver (it appears in /proc/devices), and fops is the default file_operations structure.
I am attempting to develop Linux device drivers and as my first attempt I am trying to develop a char device driver that has the following file options,
struct file_operations fops{
.open=open_fun,
.release=release_fun,
.write=write_fun,
.read=read_fun,
};
When I load the driver using insmod, I see that /proc/devices lists the driver under char devices but I can't find it in /dev. A Google search suggested use of mknod to create a deivce in /dev and associate it with the driver's major and minor. However, an attempt to do so resulted in "Permission denied" error even when done as a super user.
What should I do to make the device appear in /dev when the kernel module is loaded? I tried both the older (register_chrdev) and the newer version (cdev_init & cdev_add) of registering the device but none of them works.
Thanks,
Mir
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