> On Thu, 20 Jan 2005 04:55:20 -0800, Can Sar > <csar@xxxxxxxxxxxx> wrote: > > Hi, > > > > I wrote my own block device called sbd (using code > from > > http://lwn.net/Articles/58719/) and have currently > only been using one > > device at /dev/sbd0. I get one major number and 16 > minor numbers. From > > my understanding the number of minor numbers is > only important for > > partitions. Minor numbers are NOT used to differentiate or recognize partitions, as you said. Actually there are two device numbers, Major and Minor Numbers for each device file. These numbers are associated with each device file and they have a place in device file's inode. Major number is only important to the kernel. Actually each device driver can handle more than one device of same type or even of different types (normally its of same type, for instance you normally wont find a driver handling HDD, FDD and CD-ROM at the same time, but its possible to write such drivers). As you know system have number of devices and kernel have number of drivers to recognize those devices. When application request some action on device by using a reffernce to device file, kernel reads the major number from the inode of the device file and identifies the corresponding driver to be invoked for it. So major number are used by kernel (not device drivers) to identify which driver it need to invoke to put the device in action. Now coming to minor number of device file. once the driver functions are activated by kernel, its drivers responsibilty to manupulate the right device. As i told one driver can handle more that one device, so driver needs some mechanisum to know which device it needs to manupulate and that it comes to know by using minor number. So its two level identification, one is at kernel level (using major number to identify which driver needs to be invoked) and another at driver level (using minor number which tells which physical devices needs to be manupulated bu driver) > I also want to have other devices > like /dev/sbd1, > > /dev/sbd2, ... be supported will I need another > major number or is > there some way around this? You need not to have a seperate major number allocated for other device files. You can have one major number and different minor numbers for these different device files, as all these devices can be controlled by same driver. Note: Major numbers are limited as they are global thru out the kernel and need to be unique for each driver in kernel. This is the reason that major numbers are registered and allocated globally by linux community guys. You can see the "devices.txt" file in kernel sources Documentation directory to know the already allocated major numbers of different drivers. On other hand minor numbers are local to driver, so u can use them as per your wish in your driver code. cheers !! --gd __________________________________ Do you Yahoo!? The all-new My Yahoo! - What will yours do? http://my.yahoo.com -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
