Create System Call

Arguments: Filename (String), Permission (0 - exclusive/1 - open-access)

Return Value:

0	Success/File already exists
-1	No free inode table entry

Description : The Create operation takes as input a filename. If the file already exists, then the system call returns 0 (success). Otherwise, it creates an empty file by that name, sets the file type to DATA, file size to 0, userid to that of the process (from the process table) and permission as given in the input in the Inode Table. It also creates a root entry for that file.

Set the MODE_FLAG in the process table entry to 1, 
indicating that the process is in the create system call.

If the file is present in the system, return 0.   /* Check the Inode Table  */ 
      
Find the index of a free entry in the Inode Table. 
If no free entry found, return -1.   /* Maximum number of files reached */
             
In the Inode Table entry found above, set FILE NAME to the given file name, FILE SIZE to 0 and FILE TYPE to DATA.
In the Inode Table entry, set the block numbers to -1.  /* No disk blocks are allocated to the file */

Set the USER ID to the USERID of the process /* See the process table for user id */
Set the PERMISSION to the permission supplied as input.

In the Root file entry corresponding to the Inode Table index, 
set the FILE NAME, FILE SIZE, FILE TYPE, USERNAME and PERMISSION fields.

Set the MODE_FLAG in the process table entry to 0.

Return from the system call with 0.  /* success */
	     

Note:  At each point of return from the system call, remember to reset the MODE FLAG.

Ouestions:

1. What would happen if we do not initilize the FILE OPEN COUNT in the File Status Table to -1?