LKMs：Loadable Kernel Modules

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Loadable Kernel Modules

1. ● LKMs (Loadable Kernel Modules)
2. ● Pre-compiled binary pieces
3. ● Each piece is called “module”
4. ● Can be loaded at runtime
5. ● Extend the functionality of the system
6. ● Enforce modularity
7. ○ Easy to develop, debug and maintain
8. ○ No need to rebuild the kernel
9. ● Can save memory (load only the necessary)

What are LKMs used for

1. ● Everything that is not required in the core
2. ● 6 main categories
3. ○ Device drivers
4. ○ File system drivers
5. ■ Implementation of a specific file system
6. ○ System calls
7. ○ Network stack
8. ■ Interprets a network protocol
9. ○ TTY line disciplines
10. ○ Executable interpreters for the supported formats

Character Device Driver

1. ● Read or Write a byte at a time
2. ● Accessed by a stream of bytes
3. ● Usually permit only sequential access
4. ● Implement: open, close, read, write
5. ● Similar to regular files
6. ● Examples:
7. ○ /dev/console
8. ○ /dev/ttyS0

Block Device Driver

1. ● Read or Write block-size multiples
2. ● Permit random access
3. ● Accessed in the /dev/
4. ● File systems can be mount on top
5. ● Handle I/O operations
6. ● Differ with the char module in the way the manage data inside the kernel
7. ● Different interface to the kernel than char modules

Network Drivers

1. ● Handle any network transaction made
2. ● Transfer packets of data
3. ● Independent of a specific protocol
4. ● Reception and Transmission instead of Read/Write
5. ● Usually the interface is a hardware device but it can also be software like the loopback
6. ○ loopback is used to communicate with the servers that run in the same node, debugging etc.
7. ● They are not mapped to the file system; they are identified by a name

Praktikum Kernel Programming
University of Hamburg
Scientific Computing
Winter semester 2014/2015