[cap-talk] kernel object knowledge

[Jonathan S. Shapiro]

On Wed, 2007-05-30 at 10:09 -0700, Charles Landau wrote:
> At 1:53 PM -0400 5/29/07, Jonathan S. Shapiro wrote:
> >   2. Naive (and even sophisticated) membranes must perform
> >      storage allocation on every invocation
> 
> to wrap every capability passed
> 
> >, except where
> >      they are able to recognize a capability as EQ to some
> >      capability that they have already wrapped.
> 
> Don't these difficulties apply also to non-oblivious membranes, 
> though to a lesser degree? A non-oblivious membrane may know that 
> some capabilities do not need to be wrapped, but there may still be 
> some that do need to be wrapped. At best, a non-oblivious membrane 
> simply lowers the bound of storage required (possibly lowering it 
> from infinite to finite).

I seem to recall that MarkM had an implementation in E at one point that
was able to evade this issue by re-using the proxy object in some clever
way that I no longer recall. I may be mistaken.

I suspect (without any evidence) that the requirement to wrap (or avoid
wrapping) is a pure function of the capability type, and that oblivious
membranes can mostly implement that.

Assuming that a bounded number of capabilities are transferrable per
message, the oblivious membrane has a storage requirement that is
O(n-message). The non-oblivious membrane reduces this to
O(n-distinct-caps-xferred). Neither number is usefully small, since both
numbers considerably exceed available storage. Indeed, both requirements
likely exceed total historical world production of real storage media.


shap