The Design and Implementation of the Anykernel and Rump Kernels

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Figure 3.35: System call hijacking. The rumphijack library intercepts system
calls and determines whether the syscall request should be sent to the rump kernel
or the host kernel for processing.
selection is that there is full control of which system call goes where. The downside
is that it requires source level control and compilation. To use unmodified binaries,
we must come up with a policy which determines which kernel handles each syscall.
A key point for us to observe is that in Unix a function call API in libc (e.g.
open(const char *path, int flags, mode_t mode)) exists for all system calls.
The libc stub abstracts the details of user-kernel communication. The abstraction
makes it possible to change the nature of the call just by intercepting the call
to open() and directing it elsewhere. If the details of making the request were
embedded in the application itself, it would be much more difficult to override them
to call a remote rump kernel instead of the local host kernel.
The rumphijack library (lib/librumphijack, Figure 3.35) provides a mechanism
and a configurable policy for unmodified applications to capture and route part of