Xv6 new system calls addition

[Rahul-069]

Overview

This pull request adds three new system calls to xv6-riscv, enhancing process creation and parent-child process interaction.

System Calls Implemented

1. forkwitharg() – Creates a new process and allows passing an argument from parent to child.
2. getforkarg() – Retrieves the argument passed using forkwitharg().
3. getppid() – Returns the parent process ID of the calling process.

Files Modified

• kernel/syscall.h – Added new syscall identifiers (SYS_forkwitharg, SYS_getforkarg, SYS_getppid)
• kernel/proc.h – Added a new field fork_arg to the struct proc
• kernel/proc.c – Implemented logic for forkwitharg to handle argument passing
• kernel/sysproc.c – Added sys_forkwitharg, sys_getforkarg, sys_getppid syscall handlers
• kernel/defs.h – Declared prototypes for the new system calls
• kernel/syscall.c – Linked new system calls in the syscall table
• user/user.h – Declared the new system calls for user-space programs
• user/usys.pl – Added entries for forkwitharg, getforkarg, and getppid
• user/fork.c – User program demonstrating the use of the new system calls
• Makefile – Added the user program fork to the compilation list

Testing

• Verified functionality using the fork user program.
• All system calls execute correctly under QEMU.
• Existing xv6 functionality remains unaffected.

[djhayman]

Your code seems to have changed the line endings of all the files you touched, and the last new line you added to kernel/defs.h has incorrect indentation. And sys_getppid should not have been added to kernel/defs.h.

But ignoring formatting issues, what problem does sys_getforkarg solve? The int arg variable is already immediately available in the forked child process, your new code doesn't actually add anything new.