[cap-talk] kernel object knowledge

[Mark S. Miller]

Jonathan S. Shapiro wrote:
> On Wed, 2007-05-30 at 10:09 -0700, Charles Landau wrote:
>> 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.

You may be thinking of Bill Frantz's proposal to pre-allocate bit positions in 
the capability representation for all the membranes that a capability 
virtually passes through (link needed). This is a clever approach that shifts 
the costs around in a thought provoking way. But it's only practical if one 
can practically treat such system-supported membranes as a globally 
super-scarce resource, say 32 altogether. I expect this issue disqualifies the 
proposal for general purpose use.

-- 
Text by me above is hereby placed in the public domain

     Cheers,
     --MarkM