/**
 * @file syscall.h
 * @brief System call interface.
 *
 * Defines system call numbers and the kernel-side handler. User-mode
 * processes invoke system calls via INT 0x80 with the call number in EAX
 * and arguments in EBX, ECX, EDX, ESI, EDI.
 */

#ifndef SYSCALL_H
#define SYSCALL_H

#include <stdint.h>
#include "isr.h"

/** System call numbers. */
#define SYS_EXIT    0   /**< Exit the process. Arg: exit code in EBX. */
#define SYS_WRITE   1   /**< Write to a file descriptor. fd=EBX, buf=ECX, len=EDX. */
#define SYS_READ    2   /**< Read from a file descriptor. fd=EBX, buf=ECX, len=EDX. */
#define SYS_FORK    3   /**< Fork the current process. */
#define SYS_GETPID  4   /**< Get current process ID. */
#define SYS_YIELD   5   /**< Yield the CPU. */
#define SYS_WAITPID 6   /**< Wait for a child process. pid=EBX. */
#define SYS_EXEC    7   /**< Execute a program. path=EBX, argv=ECX. */
#define SYS_GETENV  8   /**< Get environment variable. key=EBX, buf=ECX, bufsize=EDX. */
#define SYS_SETENV  9   /**< Set environment variable. key=EBX, value=ECX. */
#define SYS_READDIR 10  /**< Read directory entry. path=EBX, idx=ECX, buf=EDX. Returns type or -1. */

/** Total number of system calls. */
#define NUM_SYSCALLS 11

/**
 * Initialize the system call handler.
 * Installs INT 0x80 in the IDT.
 */
void init_syscalls(void);

/**
 * System call dispatcher (called from the INT 0x80 handler).
 *
 * @param regs Register state at the time of the interrupt.
 */
void syscall_handler(registers_t *regs);

#endif /* SYSCALL_H */