Hey Alexandru Juncu Thank you for your help again. Sorry about that mistake, I just didn't notice the forward address when using quick reply. It won't happen again. Best. 2012/2/12 Alexandru Juncu <alex.juncu@rosedu.org>:
2012/2/12 hz hanks <hankshz@gmail.com>:
Hey Alexandru Juncu
Thank you so much! You are so helpful for me.
As far as I'm concerned, the point that confuses me is the definition of ONE device driver. For example, I would consider a file of some source codes, that manipulate the GPIO and use misc_register to register as miscdevice, as one device driver. However, I know that it will share the major device number 10 with other device drivers such as AD/DA. So how kernel works like that? In other words, how kernel works with major/minor device number? For example, will the kernel allocate some specific resources to drivers with major number 4 because it knows those drivers are for Serial ports. How about the minor number, will the kernel care about that?
Hello!
First of all, you should always reply to the list, because when there are 100 people rather than one, you have a bigger chance of getting an answer.
Is hard to define ONE device driver. Linux is a monolithic kernel. It's one big code. But linux is also modular and you can have dynamically loaded modules. But it's very flexible... you can have a module (a .ko file) that is a driver for two devices (not going to find this, but it could happend).
You usually have one .ko for one device driver for one device. This would mean one major. For example, a device driver for all the SATA devices.
[0] http://en.wikipedia.org/wiki/Monolithic_kernel
Thank you again!
2012/2/12 Alexandru Juncu <alex.juncu@rosedu.org>:
2012/2/12 hz hanks <hankshz@gmail.com>:
Hi, all
I have a question about major/minor device number. I know that one can use int register_chrdev_region(dev_t from, unsigned count, const char *name); to register a driver with a unique pair of major/minor device number. But what's the difference between two drivers: in one case they have same major device number but different minor device number; on another case they have different major device number but same minor device number. When I searched the Internet, it said that major device number is to identify the driver while the minor device number is to identify specific hardware. But I'm still confused because it seems legal to share the major device number with different drivers.
Please help meļ¼Thank you!
Hello!
I would redirect you to the /dev fs to do a long listing of its contents and notice the pattern. Devices with the same major, are usually handled by the same device driver. If that device driver needs to handle several devices, it uses an array of minors.
Example:
crw-rw---- 1 root dialout 4, 64 2011-12-12 16:25 ttyS0 crw-rw---- 1 root dialout 4, 65 2011-12-12 16:25 ttyS1 crw-rw---- 1 root dialout 4, 66 2011-12-12 16:25 ttyS2 crw-rw---- 1 root dialout 4, 67 2011-12-12 16:25 ttyS3
Notice that all the Serial ports have the same major (4) but different minors (64-67). If you do a "cat /proc/devices" you will notice that the major 4 is registered by ttyS device driver. "ttyS" is the name variable in the register_chrdev_region call.
A device driver can register zero, one ore more majors. And for each of that major, it can a number of minors (the count parameter in register_chrdev_region).
Two devices having the same minor but different majors is just a coincidence, they have nothing in common. It's just an obvious thing because a major has more minors so there will be more minors that majors.
Hope this helps.