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Lock or unlock a capability

A capability whose type matches the source-type subfield of a given lock, and has at least the same access bits on as in the access field check bits subfield of the lock, may be converted to a capability with: This is referred to as locking the capability with the given lock. Similarly, a capability may be unlocked if its type matches the target-type subfield of a given key. We also require that the access bit field of the capability have at least the same bits on as the access field of the key. The resulting capability will have: Thus, the condition: will assure that any capability resulting from an unlock operation will have previously existed, possibly with more access bits on. (We explain below how to assure this condition.) If the MOT-index unique name representation for segment capabilities is used, then a locked segment capability will contain only the MOT-index and unique name. Unlocking such a capability will cause the base-bound pair to be re-computed. Figure 7 contains an example of locking and unlocking a capability.
 
Figure 7: Example of locking and unlocking.
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next up previous contents
Next: Create a new lock Up: HARDWARE HELP Previous: Read or write the
Paul McJones
1998-06-22