3: [[!toc levels=2]]
5: # The Anykernel and Rump Kernels
7: ## About
9: A driver abstracts an underlying entity. For example, a TCP/IP driver
10: abstracts the details required to perform networking, the Fast File
11: System (FFS) driver abstracts how the file system blocks are laid out on
12: the storage medium, and a PCI network card driver abstracts how to
13: access device registers to send and receive packets. The kernel
14: architecture controls how kernel drivers run with respect to other
15: system components. Some examples of kernel architectures are the
16: monolithic kernel, microkernel and exokernel. In contrast to the above
17: architectures, NetBSD is an *anykernel*. This means that some kernel
18: drivers can be run according to any kernel architecture instead of being
19: limited to a single one.
26: When a driver is not run as part of the monolithic kernel, e.g. when it
27: is run as a microkernel style server, the driver is hosted in a *rump
28: kernel*. A rump kernel is an ultralightweight virtualized kernel running
29: on top of high-level hypercall interface. Instead of a low-level
30: hypercall API typically seen with operating systems with operations such
31: as "modify page table", the rump kernel hypercall API provides
32: high-level operations such as "run this code in a thread".
34: Currently, three implementations of the rump kernel hypercall interface
37: - The POSIX implementation is included in the NetBSD tree and allows
38: rump kernels to run as userspace processes on most operating systems
39: such as NetBSD, Linux and Solaris.
40: - The Xen implementation allows running rump kernels directly as Xen
41: DomU's without an intermediate operating system.
42: - The Linux kernel hypervisor allows rump kernels to run inside the
43: Linux kernel.
45: Rump kernels are radically different from OS virtualization technologies
46: such as KVM, containers and usermode operating systems. A rump kernel
47: does not support hosting application processes because a rump kernel is
48: aimed at virtualizing kernel drivers and application virtualization
49: would be pure overhead. Instead, existing entities such as processes
50: from a hosting OS are used as clients for the rump kernel ("application"
51: in the figure).
53: As a result of the above design choices, rump kernels are extremely
54: lightweight. The bootstrap time for rump kernels on POSIX hosts is
55: measured in milliseconds and memory footprint in 100kB's. This means
56: that a rump kernel can be bootstrapped for example as part of a command
57: line tool for virtually no cost or user impact. Rump kernels also
58: mandate very little from the hypercall implementation meaning that
59: rump kernels, and by extension NetBSD kernel drivers, can be hosted in
60: virtually any environment -- for example, rump kernels do not require
61: a platform with an MMU.
63: Use cases for rump kernels include:
65: - **Code reuse**: kernel drivers can be reused without having to run a
66: whole OS. For example, a full-featured TCP/IP stack (IPv6, IPSec,
67: etc.) can be included in an embedded appliance without having to
68: write the stack from scratch or waste resources on running an entire
70: - **Kernel driver virtualization**: every rump kernel has its own
71: state. Furthermore, the functionality offered by multiple rump
72: kernels running on the same host does not need to be equal. For
73: example, multiple different networking stacks optimized for
74: different purposes are possible.
75: - **Security**: when hosted on a POSIX system, a rump kernel runs in
76: its own instance of a userspace process. For example, it is widely
77: published that file system drivers are vulnerable to untrusted file
78: system images. Unlike on other general purpose operating systems, on
79: NetBSD it is possible to mount untrusted file systems, such as those
80: on a USB stick, in an isolated server with the kernel file system
81: driver. This isolates attacks and prevents kernel compromises while
82: not requiring to maintain separate userspace implementations of the
83: file system drivers or use other resource-intensive approaches such
84: as virtual machines.
85: - **Easy prototyping and development**: kernel code can be developed
86: as a normal userspace application. Once development is finished, the
87: code can simply be complied into the kernel. This is a much more
88: convenient and straightforward approach to kernel development than
89: the use of virtual machines.
90: - **Safe testing**: kernel code can be tested in userspace on any host
91: without risk of the test host being affected. Again, virtual
92: machines are not required.
94: ## Further Reading
96: ### Book
98: The following book is the definitive guide to the anykernel and rump
99: kernels and supercedes all earlier publications and terminology on
100: the subject.
102: - [Flexible Operating System Internals: The Design and Implementation
103: of the Anykernel and Rump
106: Note that the book was finalized in summer 2012, so while the fundamentals
107: are still accurate, some of the problems described in "Future Work"
108: have already been solved. Check out the links below.
111: ### Software using rump kernels
113: While the NetBSD source tree hosts the base kernel drivers and hypercall
114: implementation, more I/O drivers, infrastructure scripts and hypercall
115: implementations are hosted elsewhere. Most of the code is hosted
116: under the [rump kernels](https://github.com/rumpkernel/) organization
117: on github. Some highlights include:
119: - [Scripts for building rump kernels for POSIX
121: - The [rumprun](https://github.com/rumpkernel/rumprun/) package
122: allows portable building and running of unmodified NetBSD userspace
123: applications -- extremely useful for configuring rump kernels (e.g.
124: network interfaces and routing tables)
125: - [Rump kernel hypercall implementation for Xen; rump kernels as Xen
127: - [fs-utils: File system image access
129: - Fast userspace packet processing: TCP/IP stack for use with
130: [DPDK](https://github.com/rumpkernel/dpdk-rumptcpip) or
133: ### Articles, Tutorials & Howtos
135: - [Running rump kernels and applications on Xen without a full
137: - [PCI device driver support in rump kernels on
139: - [Experiment with a rump kernel hypervisor for the Linux
141: (allows rump kernels to run *in* the Linux kernel)
143: in the
145: - [Kernel Servers using
147: - [Tutorial On Rump Kernel Servers and
149: - [Revolutionizing Kernel Development: Testing With
152: ### Conference publications and talks
154: - "The Anykernel and Rump Kernels" gives a general overview and
155: demonstrates rump kernels on Windows and in Firefox. The
158: and an
160: are available. Presented at FOSDEM 2013 (Operating Systems track).
161: - "Rump Device Drivers: Shine On You Kernel Diamond" describes device
162: driver and USB. The
164: and [video presentation](http://www.youtube.com/watch?v=3AJNxa33pzk)
165: are available. Presented at AsiaBSDCon 2010.
166: - "Fs-utils: File Systems Access Tools for Userland" describes
167: fs-utils, an mtools-like utility kit which uses rump kernel file
168: systems as a backend. The
170: is available. Presented at EuroBSDCon 2009.
171: - "Rump File Systems: Kernel Code Reborn" describes kernel file system
172: code and its uses in userspace. The
176: are available. Presented at the 2009 USENIX Annual Technical
178: - "Kernel Development in Userspace - The Rump Approach" describes
179: doing kernel development with rump kernels. The
183: are available. Presented at BSDCan 2009.
184: - "Environmental Independence: BSD Kernel TCP/IP in Userspace"
185: describes networking in rump kernels. The
186: [paper](http://2009.asiabsdcon.org/papers/abc2009-P5A-paper.pdf) and
187: [video presentation](http://www.youtube.com/watch?v=RxFctq8A0WI) are
188: available. Presented at AsiaBSDCon 2009.
190: ### Manual pages
192: The manpages provide the usual type of information. Start from
193: [rump.3](http://man.NetBSD.org/cgi-bin/man-cgi?rump++NetBSD-current) and
194: follow the cross-references in "SEE ALSO".
196: ## Discuss
198: Any topic related to rump kernels can be discussed on the
199: [rumpkernel-users mailing
201: Alternatively, you can use a NetBSD mailing which is related to a
202: specific subtopic.
204: The IRC channel for rump kernels is **\#rumpkernel** on
207: ## Availability
209: The anykernel and rump kernels were first introduced as a prototype in
210: NetBSD 5.0. A stable version with numerous new features and improvements
211: was shipped with NetBSD 6.0.
213: ## Source Code
215: All of the source code is available from the NetBSD source tree and can
216: be obtained with the usual methods.
218: You can also [browse](http://cvsweb.NetBSD.org/bsdweb.cgi/src/) the
219: source code history online. Code is found from all areas of the source
220: tree. Some examples of where to look include
222: [src/usr.bin](http://cvsweb.NetBSD.org/bsdweb.cgi/src/usr.bin/) and
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