File Access

							  File Access


• The Level of the file system closest
  to the user is usually termed with the
  access method.
• The File Access method provides a
  standard interface between
  applications and the file systems and
  devices that hold the data.
Access Control Information



Owner – user who is assigned control of this file.
Access Information – a simple version of this element
                            would include the users name
and                  password for each authorized user.
Permitted Actions – Controls reading, writing,
                    executing, transmitting over a
                    network
In a Multi user systems, there is almost always a
requirement for allowing files to be shared among a
number of users. Two issues arise : Access Rights and
Management of Simultaneous Access.



File Access Rights
None                Updating
Knowledge           Changing Permission
Execution           Deletion
Reading
Appending
3 Kinds of User

Specific User – individual users who are designated by
user ID.
User Groups – a set of user who are not individually
defined.
All – all users who have access to the system. These
are public files.
Simultaneous Access

When access is granted to append or update a file
to more than 1 user, the Operating System or File
management system must enforce discipline. A
brute force approach is to allow a user to lock the
entire file system when it is to be updated. A finer
grain of control is to lock individual records
during update. Issues of mutual exclusion and
deadlock must be addressed in designing the
shared access capability.
WINDOWS NTFS File and Directory Attribute
Types

 Standard Info
 Attribute List
 File Name
 Security Descriptor
 Data
 Index Root
 Index Allocation
 Volume Info
 Bitmap