The Design and Implementation of the Anykernel and Rump Kernels

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int
RUMP_VOP_READ(struct vnode *vp, struct uio *uio, int ioflag, struct kauth_cred *cred)
{
int error;
rump_schedule();
error = VOP_READ(vp, uio, ioflag, cred);
rump_unschedule();
}
return error;
Figure 3.14: Implementation of RUMP_VOP_READ(). The backend kernel call
is wrapped around the rump kernel entrypoint and exitpoint.
The rump vnode interface exports the vnode interfaces to rump kernel clients. The
intended users are microkernel file servers which use rump kernels as backends. The
benefits for exporting this interface readily are the ones we listed in the beginning of
this section: a prototype for client code and automated entry/exit point handling.
The wrappers for the vnode interface are simpler than those of the system call
interface. This simplicity is because there is no need translate parameters and we
can simply pass them on to the kernel internal interface as such. To distinguish
between the internal implementation and the rump application interface, we prefix
rump client vnode interfaces with RUMP_.
The kernel vnode interface implementations and prototypes are autogenerated from
the file sys/kern/vnode_if.src by sys/kern/vnode_if.sh. We made the script
to generate our prototypes into sys/rump/include/rump/rumpvnode_if.h and
wrapper functions into sys/rump/librump/rumpvfs/rumpvnode_if.c. Anexample
result showing the RUMP_VOP_READ() interface is presented in Figure 3.14. The
VOP_READ() routine called by the wrapper is the standard implementation which is
extracted into a rump kernel from sys/kern/vnode_if.c.