creat.c

#include "stdio.h"
#include "filesys.h"
int creat(unsigned int user_id, char *filename, unsigned short mode)
{
  unsigned int di_ith, di_ino;
  struct inode *inode;
  int i, j, k, user_p;

  for (user_p = 0; user_p < USERNUM; user_p++)
    if (user[user_p].u_uid == user_id)
    {
      k = user_p;
      break;
    }

  di_ino = namei(filename);

  if (di_ino != NULL) /*already existed*/
  {
    inode = iget(di_ino);
    if (access(user_id, inode, mode) == 0)
    {
      iput(inode);
      printf("\ncreat access not allowed\n");
      return;
    }

    /*free all the block of the old file */
    for (i = 0; i < inode->di_size / BLOCKSIZ + 1; i++)
      bfree(inode->di_addr[i]);

    /*to do: add code here to update the pointer of the sys_file*/
    for (i = 0; i < SYSOPENFILE; i++)
      if (sys_ofile[i].f_inode == inode)
        sys_ofile[i].f_off = 0;

    for (i = 0; i < NOFILE; i++)
      if (user[k].u_ofile[i] = SYSOPENFILE + 1)
      {
        user[k].u_uid = inode->di_uid;
        user[k].u_gid = inode->di_gid;
        for (j = 0; j < SYSOPENFILE; j++)
          if (sys_ofile[j].f_count = 0)
          {
            user[k].u_ofile[i] = j;
            sys_ofile[j].f_flag = mode;
          }
        return i;
      }
  }
  else /*not existed before */
  {
    inode = ialloc();
    di_ith = iname(filename);

    dir.size++;
    dir.direct[di_ith].d_ino = inode->i_ino;

    inode->di_mode = user[k].u_default_mode | DIFILE;
    inode->di_uid = user[k].u_uid;
    inode->di_gid = user[k].u_gid;
    inode->di_addr[0] = balloc();
    inode->di_size = 0;
    inode->di_number = 1;

    for (i = 0; i < SYSOPENFILE; i++)
      if (sys_ofile[i].f_count == 0)
        break;

    for (j = 0; j < NOFILE; j++)
      if (user[k].u_ofile[j] == SYSOPENFILE + 1)
        break;

    user[k].u_ofile[j] = i;
    sys_ofile[i].f_flag = mode;
    sys_ofile[i].f_count = 0;
    sys_ofile[i].f_off = 0;
    sys_ofile[i].f_inode = inode;
    return j;
  }
}