The Design and Implementation of the Anykernel and Rump Kernels

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since the representation might not be the same in the kernel and the hypercall
library. Even different versions of NetBSD have different representations, for
example due to increasing time_t from 32bit to 64bit. Therefore, to have
a well-defined interface when running on a non-native host, the hypercall
interface should only use data types which are the same regardless of ABI. For
example, the C99 constant width type uint64_t is preferred over time_t.
Since the hypercall executes in the same process as the rump kernel, byte
order is not an issue, and the native one can be used.
3. A separate interface helps future investigation of running rump kernels on
non-POSIX platforms, such as microkernels. This investigation, however,
will require adjustments to the hypercall interface. While the need for adjustments
is foreseeable, the exact forms of the adjustments are not, and that
is the reason they are not already in place.
The header file sys/rump/include/rump/rumpuser.h defines the hypercall interfaces.
All hypercalls by convention begin with the string “rumpuser”. This prevents
hypercall interface references in the rump kernel from falling under the jurisdiction
of symbol renaming.
We divide the hypercall interfaces into mandatory and optional ones. The routines
that must be implemented by the rumpuser library are:
• memory management: allocate aligned memory, free
• thread management: create and join threads, TLS access
• synchronization routines: mutex, read/write lock, condition variable.
This class is illustrated in Figure 3.3.
• exit: terminate the host container. In a POSIX environment depending on
the parameters termination is done by calling either abort() or exit().