Character Device Modules

Character device modules are KLDs that create or install a character device. In FreeBSD, a character device is the interface for accessing a specific device within the kernel. For example, data is read from and written to the system console via the character device /dev/console.

Note

In Chapter 4 you'll be writing rootkits that hack the existing character devices on the system. Thus, this section serves as a primer.

There are three items that are unique to each character device module: a cdevsw structure, the character device functions, and a device registration routine. We'll discuss each in turn below.

The cdevsw Structure

A character device is defined by its entries in a character device switch table, struct cdevsw, which ...

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