NetBSD/usermode (Was: CVS commit: src)

["Valeriy E. Ushakov" <uwe%stderr.spb.ru@localhost>]

On Wed, Dec 21, 2011 at 16:47:49 +0100, Reinoud Zandijk wrote:

> From the beginning of the usermode project, we struggled with the
> fact that system calls in usermode's userland will go to the wrong
> kernel [...]

Because you chose to run userland code in the same process with the
usermode kernel code, which is a rather controversial design choice,
IMO.  E.g. how do you prevent userland code from accessing pages it's
not meant to access, i.e. how do you emulate MMU?


> We've tried to tackle this with ptrace constructions including the
> PTRACE emul stuf but that turned out to be a dead-end since ptrace
> was never designed to allow redirection or interception of system
> calls.

This statement seems ... strange (cf. PT_SYSCALL).  Can you elaborate?


> On top of that, it also turned out to be agonizing slow.

How slow?  What are your target performance numbers?  What are your
primary intended uses for the usermode kernel, in general?


On Thu, Dec 22, 2011 at 15:31:45 +0000, David Holland wrote:

> Consequently, the changes should be reverted, at least until the
> design has been gone through carefully.

Seconded.


-uwe