Code that handles interrupts, on the other hand, is asynchronous with respect to processes and is not related to any particular process. This code attempts to register three fictitious facilities. Four FIFO first-in-first-out devices, which act like pipes. If, on the other hand, you are just trying to write a device driver for your own device, and you don’t want to muck with the kernel internals, the text should be modularized enough to fit your needs as well. What would be a good source for those example files used in LDD book? The reason is that the script must be run by the superuser, so newly created special files are owned by root.

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Modules are strongly tied to the data structures and function prototypes defined in a particular kernel version; the interface seen by a module can change significantly from one kernel version to the next. Also is the link to their source code. Note, however, that there is a slow but steady drift toward frame-buffer-based graphics environments, where the X server acts only as a server based on a real kernel-space device driver for actual graphic manipulation.

Each computer platform has its peculiarities, and kernel designers are free to exploit all the peculiarities to achieve better performance in the target object file. The above line is not how a traditional makefile looks, after all.

With debugging and concurrency management skills in place, we move to advanced features of char drivers, such as blocking operations, the use of selectand the important ioctl call; these topics are the subject of Chapter 6. Here, first is the beginning device number of the range you would like to allocate. If the two issues are addressed by different parts of the program, or even by different programs altogether, the software package is much easier to develop and to adapt to particular needs.


First of all, the incredible patience of Federica, who went as far as letting me review the first edition during our honeymoon, with a laptop in the tent.

Bear in mind that your module’s code has to be recompiled for each version of the kernel that it is linked to—at least, in the absence of modversions, not covered here as they are more for distribution makers than developers. Errors are signaled by a negative return value. The return value, if nonnegative, represents the number of bytes successfully written. Though it may appear strange to say that a driver is “flexible,” we like this word because it emphasizes that the role of a device driver is providing mechanismnot policy.

Developers experimenting with new devjce, however, want to be running the latest development release. It must deviice included by a module source. Those who run odd-numbered versions of the kernel are usually skilled enough to dig in the code without the need for a textbook, which is another reason why we don’t talk about development kernels here.

The printk function is defined in the Linux kernel and made available to modules; it behaves similarly to the standard C library function printf.

Essentially, the double underscore says to the programmer: This code attempts to register three fictitious facilities. But ld3 copyrights on the kernel are held by many developers, and not all of them agree that kernel modules are not derived products. The kernel builds a structured filesystem on top of unstructured hardware, and the resulting file abstraction is heavily used throughout the whole system.

Where drivers are concerned, the same separation of sevice and policy applies.

Linux Device Drivers, 3rd Edition

Chapter 14 is a bottom-up look at the device model infrastructure, starting with the kobject type and working up from there. Also, for everyone who has ever sent me bug reports, critiqued my code, and flamed me for doing stupid things, you have all taught me so much about how to be a better programmer and, throughout it all, made me feel very welcome to be part of this community.


Sometimes, however, some policy decisions must be made.

The permission bits default so that only root has linyx access, while anyone can get read access. So far, we have reserved som e device numbers for our use, but we have not yet connected any of our driver’s operations to those numbers.

Come along; we can always use the help. It is possible to configure the kernel to allow “forced” removal of modules, even when they appear to be busy.

examples / Linux Device Drivers 3rd Edition · GitLab

As a device lunux writer, you should be aware of situations in which some types of device access could adversely affect the system as a whole and should provide adequate controls. So your code must be prepared to be called as soon as it completes its first registration. It is not strictly necessary, but your module really should specify which license applies to its code. Often, the module can continue to operate after a registration failure, with degraded functionality if necessary.

These markers work by causing the relevant objects to be placed in a special ELF section in the executable file. This organization is meant to allow you to test the software on your own computer as far as possible without the need to plug external hardware into the machine.

Once that task is taken care of, you’ll be ready to start playing with kernel modules.