Managing and Developing Dynamically Loadable Kernel Modules

Developing Dynamically Loadable Kernel Modules

Chapter 12560

4. Execute the following command to generate the dlclass driver: make.

The make (1) command examines the local Makefile and generates

the dlclass driver according to the rules in the Makefile. It

compiles dlclass.c into mod.o. It then installs and conﬁgures the

driver. The make command also loads the driver and extracts the

dynamically assigned major number used to create device special ﬁle

/dev/dlclass.

You can read a message from dlclass by executing the following

command: cat /dev/dlclass. The following message prints on your

computer screen: “Reading from loadable WSIO driver ‘dlclass’.”

You can write a message to dlclass by executing a command such as

echo Hello Hello > /dev/dlclass. To see the output, execute the

following command: dmesg | tail. The system responds as follows:

dlclass> OPEN -- write buffer size = 40

dlclass> ’Hello Hello’

dlclass> CLOSE

But if you write a message more than 40 characters, (cp master

/dev/dlclass, for example), the write() system call will fail because

dlclass cannot remember such a long word. You can change the

maximum length of the message by using kmtune -s to set the tunable

parameter dlclass_bufsz to a higher value.

NOTE When dlclass is unloaded (kmadmin -U dlclass), you can auto load

dlclass by executing a command such as cat /dev/dlclass.