RUMP(3)

NAME
rump - Rump Kernel

LIBRARY
rump Library (librump, -lrump)

SYNOPSIS
#include <rump/rump.h>

DESCRIPTION
A rump kernel is a virtualized kernel instance which retains only part of the NetBSD kernel. Rump kernels are aimed at virtualizing kernel drivers and do not support for example creating processes, managing virtual memory address spaces or scheduling threads. These features are unnecessary overhead when virtualizing drivers. Rump kernels are created by linking a desired set of components together. On NetBSD, these components are available as userspace libraries with the prefix librump. The high-level rumpuser(3) hypercall interface is used by a rump kernel to request resources and services from the host it runs on. Like any virtualized kernel, a rump kernel also provides its own set of namespaces, such as a file system hierarchy and TCP ports, that are independent of the ones on the host and of any other rump kernel instances. It should be noted that the presence of the provided namespaces depends on the components that the rump kernel was constructed with.

Since a rump kernel does not provide support for applications processes, existing entities are used as rump kernel clients. The relationship between the client and the rump kernel defines the execution model of the rump kernel. A local client will reside in the same address space and manipulate the rump kernel with function calls and direct memory references. Remote and microkernel clients are disjoint from the rump kernel and make requests though various protocols, see for example p2k(3), rump_sp(7), and rumphijack(3). Remote clients will also work over a TCP/IP network, or other similar communication medium.

A rump kernel is bootstrapped by calling rump_init(). A number of environment variables set before a rump kernel is bootstrapped will affect how it works. Some examples include:

RUMP_NCPU
    If set, indicates the number of virtual CPUs configured into a rump kernel. The default is the number of host CPUs. The number of virtual CPUs controls how many threads can enter the rump kernel simultaneously.

RUMP_VERBOSE
    If set to non-zero, activates bootverbose.

RUMP_THREADS
    If set to 0, prevents the rump kernel from creating any kernel threads. This is possible usually only for file systems, as other subsystems depend on threads to work.

RUMP_MEMLIMIT
    If set, indicates the maximum amount of memory that a rump kernel will request from the hypervisor via rumpuser_malloc(). When the rump kernel is close to the allocation limit, it will attempt to make more memory available by flushing its caches. The default is as much as the host allows.

RUMP_NVNODES
    Sets the value of the kern.maxvnodes sysctl node to the indicated amount. Adjusting this may be useful for example when testing vnode reclaim code paths. While the same value can be set by means of sysctl, the env variable is often more convenient for quick testing. As expected, this option has effect only in rump kernels which support VFS. The current default is 1024 vnodes.

The standardized way for a client to make requests into a rump kernel is to use rump kernel system calls, which have equivalent syntax and semantics with regular NetBSD system calls. The parameters are expected to be in the NetBSD type system unless a system call translation component, for example librumpkern_sys_linux, is linked into the rump kernel, in which case system call parameters will be automatically translated from the client type system into the NetBSD type system and back. The rump kernel system calls are made available to a client by including <rump/rump_syscalls.h>. It is also possible to configure unmodified binaries to make syscalls into a rump kernel with rumphijack(3).

SEE ALSO
rump_server(1), p2k(3), rump_etfs(3), rump_lwproc(3), rumpclient(3), rumphijack(3), rumpuser(3), ukfs(3), rump_sp(7) Antti Kantee, 2012, Aalto University Doctoral Dissertations, Flexible Operating System Internals: The Design and Implementation of the Anykernel and Rump Kernerls. Antti Kantee, June 2009, Proceedings of the 2009 USENIX Annual Technical Conference, pp. 201-214, Rump File Systems: Kernel Code Reborn. Arnaud Ysmal, Antti Kantee, September 2009, EuroBSDCon 2009, Fs-utils: File Systems Access Tools for Userland. Antti Kantee, March 2009, Proceedings of AsiaBSDCon 2009, pp. 71-80, Environmental Independence: BSD Kernel TCP/IP in Userspace. Antti Kantee, March 2010, Proceedings of AsiaBSDCon 2010, pp. 75-84, Rump Device Drivers: Shine On You Kernel Diamond. Antti Kantee, May 2009, BSDCan 2009, Kernel Development in Userspace - The Rump Approach.

Web page with more information, including links to the publications: http://www.NetBSD.org/docs/rump/

HISTORY
Rump kernels appeared as an experimental concept in NetBSD 5.0. The first stable version was released in NetBSD 6.0.

AUTHORS
Antti Kantee <pooka@iki.fi>