Build A New Kernel and Add New System Calls in A Linux OS jlchou@csie.nctu.edu.tw C.L. Chou

Goals Learn how to build a new Linux kernel Learn how to add new system calls

Build A New Linux Kernel

Reference Refer to relative documents on Internet Use “how to build a linux kernel” as key words for search engine. E.g. http://www.digitalhermit.com/linux/Kernel-Build-HOWTO.html

Note for Kernel Configuration File system support RAM disk support may need to be checked when configuring the kernel. Device Drivers  Block devices  RAM disk support Network devices’ drivers have to be checked according to what kinds of network devices equipped on your PC.

Note for Kernel Compilation and Installation Basic installation steps: %make xconfig/menuconfig %make dep %make clean %make bzImage %make modules %make modules_install %make install Automatically copy kernel image, copy system.map, create initial ramdisk, modify grub.conf, etc.

Add New System Calls

Reference Refer to relative documents on Internet Use “how to add a system call” as key words for search engine. E.g. http://fossil.wpi.edu/docs/howto_add_systemcall.html

Added or Modified Kernel Files The version of example kernel is 2.6.11.1 Files added or modified in the kernel: arch/i386/kernel/syscall_table.S (split from entry.S) include/asm/unistd.h include/linux/myservice.h include/net/myvariable.h net/ipv4/myservice.c init/main.c net/ipv4/tcp.c

Functionalities of added system calls mysetflag() Turn on/off a kernel flag to start/stop counting the number of invoking tcp_sendmsg() in the kernel. mygetdata() Obtain the number of invoking tcp_sendmsg() recorded in the kernel.

arch/i386/kernel/syscall_table.S Modified file Search key words: sys_mysetflag sys_mygetdata

include/asm/unistd.h Modified file Search key words: mysetflag mygetdata #define NR_syscalls 313 313 is the total number of system calls.

include/linux/myservice.h Added file The header file of net/ipv4/myservice.c

include/net/myvariable.h Added file Declaration of two global variables and one data structure which are used in kernel.

net/ipv4/myservice.c Added file Define two system call functions and one initialization function. sys_mysetflag() sys_mygetdata() myvariable_init()

init/main.c Modified file Search key word: myvariable_init (twice)

net/ipv4/tcp.c Modified file Search key words: myflag (twice) tcp_sendmsg_call_count (twice)

User-level Example Program Files myservice_user.h myservice_user.c Compiling myservice_user.c gcc –o myservice_user myservice_user.c

Demo Date: 4/24 (Mon.), 4/25(Tues.) at EC215 Steps: Run the user-level program. Run any application that creates a TCP connection to send data packets. ssh ftp http

Downloading FTP Site IP: 140.113.214.77 Port: 21 Login: homework Password: homework Files: Build A New Kernel and Add New System Calls.ptt linux-2.6.16.1.tar.gz myservice_user.tar.gz