Question

In a ring-based system, procedure p is executing and needs to invoke procedure q. Procedure q's access bracket is (5,6,9). In which ring(s) must p execute for the following to happen?

Answer 1

Complete Question:

Consider Multics procedures p and q. Procedure p is executing and needs to invoke procedure q. Procedure q's access bracket is (5, 6) and its call bracket is (6, 9). Assume that q's access control list gives p full (read, write, append, and execute) rights to q. In which ring(s) must p execute for the following to happen?

A) p can invoke q, but a ring-crossing fault occurs.

B) p can invoke q provided that a valid gate is used as an entry point.

C) p cannot invoke q.

D) p can invoke q without any ring-crossing fault occurring, but not necessarily through a valid gate

Answer:

If we suppose the access bracket as (a, b) and call bracket as (b, c), for q we have (a, b) = (5, 6) and (b, c) = (6, 9). Let the ring be denoted by r.

A) p can invoke q, but a ring-crossing fault occurs.

p must execute in rings where r < a., in r < 5, p must execute.

B) p can invoke q provided that a valid gate is used as an entry point.

p must execute in the rings between 6 and 9. r must be between a and b.

C) p cannot invoke q.

When r > c, then p cannot invoke q. That means, for this condition to happen p must execute in rings > 9

D) p can invoke q without any ring-crossing fault occurring, but not necessarily through a valid gate

When r is between a and b then the condition can be satisfied. That means p must execute in rings between 5 and 6.

Explanation:

Answer 2

Answer:

A.Rings 0 through 4

B. Rings 7 through 9

C.Ring number greater than 9

D.Riing 5 or 6

Explanation

(a)p can invoke q, but a ring-crossing fault occurs. R< a1 for access permitted but ring crossing fault occurs. Therefore, go through - rings 0 through 4.

(b)p can invoke q provided a valid gate is used as an entry point.

A2 < r <= a3 for access allowed if make through a valid gate. Therefore, go through - rings 7 through 9.

(c)p cannot invoke q.

a3 < r for all access denied. Hence, proceed through - ring with number greater than 9.

(d)p can invoke q without any ring-crossing fault occurring, but not through a valid gate.proceed through – ring 5 or 6.