yes . we can have .
The minor number is used only by the driver itself to differentiate which device it's operating on, just in case the driver handles more than one device.
(or)
one driver can control more than one device .minor will be used to distinguish the one device from other devices .
mknod is a command which used create the device file (or) node in Linux file system.
In unix or linux we will represent everything as a file .
syntax: mknod Name { b | c } Major Minor
Name : name of the device file
{ b | c } : type of device (ex; char or block device)
Major : Major number of the device file
Minor : Minor number of the device file
ex : $ mknod /dev/rama c 12 5
MKDEV(int major, int minor);
It's an integer number mainly used to provide the association between the device driver and device file . this number is used by kernel .
(or)
The major number tells you which driver handles which device file.
if you have the major and minor numbers and need to turn them into a dev_t, use:
register_chrdev_region works well if you know ahead of time exactly which device numbers you want. Often, however, you will not know which major numbers your device will use; there is a constant effort within the Linux kernel development community to move over to the use of dynamically-allocated device numbers.
allocation : init function of a module
freeing : cleanup function of a module
register_chrdev_region() function will statically allocate device numbers. which is declared in <linux/fs.h>
int register_chrdev_region(dev_t first, unsigned int count, char *name);
Return values : In case of success "0" will return , In case of failure "-1 or negative value " will return
Here
In 2 ways we can allocate device numbers
void unregister_chrdev_region(dev_t first, unsigned int count);
To obtain the major or minor number of a dev_t, use:
MAJOR(dev_t dev); // to obtain major number
MINOR(dev_t dev); // to obtain minor number
int major=MAJOR(dev_t dev);
int minor =MINOR(dev_t dev);
alloc_chrdev_region()will dynamically allocate device numbers.
int alloc_chrdev_region(dev_t *dev, unsigned int firstminor,
unsigned int count, char *name);
Here
Some major device numbers are statically assigned to the most common devices. A list of those devices can be found in Documentation/devices.txt within the kernel source tree.
The disadvantage of dynamic assignment is that you can't create the device nodes in advance, because the major number assigned to your module will vary.
This is used to hold device numbers—both the major and minor parts.