[coyotos-dev] SPAM-LOW: FCRB concept is broken

[Jonathan S. Shapiro]

On Tue, 2007-02-13 at 10:08 -0500, Sandro Magi wrote:

> I must be missing something. Why can't fcrb.c0 be updated while the
> preemption handler is running, or on preemption return?

Updating FCRB.c0 isn't the problem. Delivering FCRB.c0 to a capability
register isn't the problem.

The problem is that this delivery happens during an interrupt. This
means that:

  1. The *old* content of the receiving register must be saved
     (this part can be done).

  2. On return from activation, the activation handler must be
     able to *restore* that register.

     This is where the problem is, because this cannot be done
     without a system call, and an extra system call in this path
     is prohibitively expensive.

shap
-- 
Jonathan S. Shapiro, Ph.D.
Managing Director
The EROS Group, LLC
+1 443 927 1719 x5100