Homework 9

22C:116, Fall 2000

Due Friday Oct 27, 2000, in class

Background: Consider a Demos like operating system, with the primitives:

cap = create( box )

returns a capability allowing a process to send messages to the designated box of the caller.

send( msg, cap )

sends a message to the recipient process and box indicated by a capability, where messages may contain any mixture of capabilities and other data.

msg = receive( box )

receive a message from the indicated box of the caller; if none are present in the box, block until a message is available.

The process manager

* creation box - on receipt of a message <rcap>, creates an empty and returns a management capability via the capability rcap. New processes have uninitialized memory and registers, and have no capabilities in their capability lists.

* management box - for each process in the system, the process manager has a box that accepts service requests such as stop, start, delete, and write. The management capability for that process addresses this box! Delete causes the process to be destroyed. Start makes the process a candidate for scheduling. Stop removes the process from the control of the scheduler, and the write operations can be used to request the process manager to store particular data in the code setment of the process, to modify the registers of the process, or to store particular capabilities in the C-list of the process.

The file manager

* creation box - on receipt of a message <rcap>, creates an empty file and returns a capability for that file via the capability rcap.

* file box - for each file in the file system, the file manager has a box that accepts service requests such as delete, read and write. Delete causes the file to be destroyed. Read and write allow the file to be manipulated.

The window manager

* creation box - on receipt of a message <rcap>, creates a window and returns a capability for that window via the capability rcap.

* window box - for each window, the window manager has a box that accepts service requests such as delete, start, stop, read and write. Delete causes the window to be destroyed. Start and stop cause the window to be exposed or hidden, read and write allow interaction with the user through the window.

1. A Problem What capabilities would you suggest should be included in the "standard environment" of a process running under this system. The standard environment should include all capabilities that every process might require in order to interact with the system and with its environment. Of course, any particular process may require nonstandard extenstions to this environment, but these should not be considered here.

2. A Problem Outline a protocol by which a user process could create a new process and start it running a particular object file, where the new process runs in the environment of its caller. Your protocol should be documented from the user's perspective.

3. A Problem The example system presented for this assignment has no access rights associated with capabilities. Suggest the kinds of rights you might wish for in developing systems based on this set of servers.

4. A Problem What minimium facilties are missing from this system to allow users to develop protocols for dealing with lost messages during a clinet-server interaction.

5. A Problem Suppose you wanted to write a server under this system. Your server will need to wait for any request from any client. Unfortunately, the set of services documented here does not suffice for this. Propose a solution to this problem. You might want to look at the select service under the UNIX system.