Note: Introduction

####Traps

• Invoking the kernel from user code
• Done by system calls
• Handled as part of the program that caused it

####Interrupts

• A request from an external device for a response from the processor.
• Handled independently of any user program

####Address space

• Stack
• going down
• going up
• Dynamic
• BSS(block started by symbol)
• Data
• Text

####Process Management

• fork()
• wait(&ReturnCode)
• exit(n)
• 1. process calls exit- zombie state(PID and return value preserved)
  2. parent process calls wait- released(all traces disappear)
• parent terminates before the child PID 1 inherits the children of terminated processes

####Exec(s)

• creates a new process to replace the program with a new one
• execl(name of file, name of program, command-line arguments terminating with 0)
• What if the size doesn’t match up? The new process image will have different address spaces for text, data, BSS, Dynamic and Stack according to the new process.

####File Descriptors

• How many file descriptor table? Each process have different file descriptor table residing in the shell

• Both file descriptors refer to the same context info

    close(1);
    close(2);
    dup(1);
  

####Pipe

int p[2];
pipe(p);
// p[0] for read
// p[1] for write

####Links

• Hard link: link system call or ln
• Symbol link: symlink system call or ln -s

####execve

execve(const char *path, char *const argv[], char*const envp[]);

• path is the path to the program
• argv
  • The first element in argv is the name of the executed program(eg: last component of path, or whatever)
  • The rest elements in args are argumentlist, terminated by NULL
• envp
  • Environment pointer, null-terminated
  • see environ(7)

####Bear in mind: some realations

• Every time you malloc, you have to free
• Every time you open, think about close