Lab 3 System Call Operating System Lab NCHU

Lab 3 System Call Operating System Lab NCHU System & Network Lab

What is a System Call? (1/3) • System call provide the interface between a process and an operation system. – The mechanism used by an application program to request service from the operating system NCHU System & Network Lab

What is a System Call? (2/3) • System calls can be grouped roughly into five major categories： – – – Process control File management Device management Information maintenance Communications NCHU System & Network Lab

What is a System Call? (3/3) NCHU System & Network Lab

How to Add a System Call (1/9) • STAGE 1: Add system call and then make kernel – The implementation of system calls is within the kernel – Thus, if we add a new system call • Kernel is changed • Re-make and re-install the kernel • STAGE 2 : Add a user program and call system call – Test the correction of our new system call NCHU System & Network Lab

How to add a system call(2/9) • STAGE 1: Make Kernel and add system call – 1. Downlaod new Source Code from www. kernel. org to /usr/src. – 2. [root@localhost~ ]#tar -zxvf linux-2. 6. 22. 6 tar. gz // Un-compress and un-archive NCHU System & Network Lab

How to Add a System Call (3/9) – 3. – Edit file /usr/src/ linux-2. 6. 22. 6 /arch/i 386/kernel/syscall_table. S – Put a new system call into system_call_table [root@localhost~ ]#vim /usr/src/ linux-2. 6. 22. 6 /arch/i 386/kernel/syscall_table. S – We will see the code like this in this file: . data ENTRY(sys_call_table). long sys_ni_call /* 0 */ …… – At the bottom of sys_call_table, create a new system call name – For example: • . long sys_myservice /* 324 */ NCHU System & Network Lab

How to Add a System Call(4/9) – 4. – Write the code of the new system call [root@localhost~ ]# vim /usr/src/linux 2. 6. 22. 6/arch/i 386/kernel/myservice. c – We want to print “*******This is my new system call****” #include <linux/linkage. h> #include <linux/kernel. h> asmlinkage int sys_myservice(void) { printk(“****This is my new system call****n”); return 0; } NCHU System & Network Lab

How to Add a System Call (5/9) – 5. – Edit file /usr/src/ linux-2. 6. 22. 6 /arch/i 386/kernel/Makefile – We need to re-make our kernel so that the new system call can be in effect • Add our new system call file into the kernel’s makefile. – Also compiler the code of new system call when compiling the kernel • [root@localhost~ ]# vim /usr/src/linux 2. 6. 22. 6/arch/i 386/kernel/Makefile obj-y += myservice. o NCHU System & Network Lab

How to Add a System Call (6/9) – 6. – build system call 「stub」to allow user program call this system call • [root@localhost~ ]#vim /usr/src/linux-2. 6. 22. 6/include/asm-i 386/unistd. h – The content of this file likes this： … #define __NR_io_destroy 246 #define __NR_io_getevents 247 #define __NR_io_submit 248 #define __NR_io_cancel 249 …. – Add #define __NR_(name) #define __NR_myservice 324 – The number of total system call is added one #define __NR_syscalls 325 NCHU System & Network Lab

How to Add a System Call (7/9) – 7. – Make new kernel contaning the new system call • make mrproper – remove all generated files + config + various backup files • make menuconfig – Use text mode to select what drivers or modules that we want to use. • make modules – Compile modules • make modules_install – Install modules in /lib/modules/linux-2. 6. 22 • make – Compile kernel • make install – Install kernel • [root@localhost~ ]# make modules && make modules_install && make install NCHU System & Network Lab

How to Add a System Call (8/9) • STAGE 2 : Write a new user program to test the system call – 1. – Write a new user program [root@localhost~ ]#vim testsyscall. c #include <linux/unistd. h> #define __NR_myservice 324 _syscall 0(int、myservice); int main () { myservice(); return 0; } NCHU System & Network Lab

How to Add a System Call (9/9) – 2. – Compile this file • [root@localhost~ ]#gcc -Wall testsyscall. c -o testsyscall. o – 3. – It’s show time • [root@localhost~ ]#. /testsyscall. o NCHU System & Network Lab

Reference • Operation system concepts sixth edition • Wikipedia – http: //en. wikipedia. org/wiki/System_call • 鳥哥的 Linux 私房菜 – http: //linux. vbird. org/ • Google – Search key word “system call” NCHU System & Network Lab