sysfile.c

#include "types.h"
#include "stat.h"
#include "param.h"
#include "mmu.h"
#include "proc.h"
#include "defs.h"
#include "x86.h"
#include "traps.h"
#include "syscall.h"
#include "spinlock.h"
#include "buf.h"
#include "fs.h"
#include "fsvar.h"
#include "file.h"
#include "fcntl.h"

// Fetch the nth word-sized system call argument as a file descriptor
// and return both the descriptor and the corresponding struct file.
static int
argfd(int argno, int *pfd, struct file **pf)
{
  int fd;
  struct file *f;

  if(argint(argno, &fd) < 0)
    return -1;
  if(fd < 0 || fd >= NOFILE || (f=cp->ofile[fd]) == 0)
    return -1;
  if(pfd)
    *pfd = fd;
  if(pf)
    *pf = f;
  return 0;
}

// Allocate a file descriptor for the given file.
// Takes over file reference from caller on success.
static int
fdalloc(struct file *f)
{
  int fd;

  for(fd = 0; fd < NOFILE; fd++){
    if(cp->ofile[fd] == 0){
      cp->ofile[fd] = f;
      return fd;
    }
  }
  return -1;
}

int
sys_read(void)
{
  struct file *f;
  int n;
  char *cp;

  if(argfd(0, 0, &f) < 0 || argint(2, &n) < 0 || argptr(1, &cp, n) < 0)
    return -1;
  return fileread(f, cp, n);
}

int
sys_write(void)
{
  struct file *f;
  int n;
  char *cp;