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    1: **Contents**
    2: 
    3: [[!toc levels=2]]
    4: 
    5: # The Anykernel and Rump Kernels
    6: 
    7: ## About
    8: 
    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.
   20: 
   21: <!--
   22:     TODO
   23:     ![](rumparch.png)
   24: -->
   25: 
   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".
   33: 
   34: Currently, three implementations of the rump kernel hypercall interface
   35: exist.
   36: 
   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.
   44: 
   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).
   52: 
   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.
   62: 
   63: Use cases for rump kernels include:
   64: 
   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
   69:     OS.
   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.
   93: 
   94: ## Further Reading
   95: 
   96: ### Book
   97: 
   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.
  101: 
  102: -   [Flexible Operating System Internals: The Design and Implementation
  103:     of the Anykernel and Rump
  104:     Kernels](http://lib.tkk.fi/Diss/2012/isbn9789526049175/isbn9789526049175.pdf)
  105: 
  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.
  109: 
  110: 
  111: ### Software using rump kernels
  112: 
  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:
  118: 
  119: -   [Scripts for building rump kernels for POSIX
  120:     systems](https://github.com/rumpkernel/buildrump.sh)
  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
  126:     DomU's](https://github.com/rumpkernel/rumpuser-xen)
  127: -   [fs-utils: File system image access
  128:     utilities](https://github.com/stacktic/fs-utils)
  129: -   Fast userspace packet processing: TCP/IP stack for use with
  130:     [DPDK](https://github.com/rumpkernel/dpdk-rumptcpip) or
  131:     [netmap](https://github.com/rumpkernel/netmap-rumptcpip)
  132: 
  133: ### Articles, Tutorials & Howtos
  134: 
  135: -   [Running rump kernels and applications on Xen without a full
  136:     OS](http://blog.NetBSD.org/tnf/entry/running_applications_on_the_xen)
  137: -   [PCI device driver support in rump kernels on
  138:     Xen](http://blog.NetBSD.org/tnf/entry/pci_driver_support_for_rump)
  139: -   [Experiment with a rump kernel hypervisor for the Linux
  140:     kernel](http://blog.NetBSD.org/tnf/entry/a_rump_kernel_hypervisor_for)
  141:     (allows rump kernels to run *in* the Linux kernel)
  142: -   [Experiment on compiling rump kernels to javascript and running them
  143:     in the
  144:     browser](http://blog.NetBSD.org/tnf/entry/kernel_drivers_compiled_to_javascript)
  145: -   [Kernel Servers using
  146:     Rump](http://www.NetBSD.org/docs/rump/sysproxy.html)
  147: -   [Tutorial On Rump Kernel Servers and
  148:     Clients](http://www.NetBSD.org/docs/rump/sptut.html)
  149: -   [Revolutionizing Kernel Development: Testing With
  150:     Rump](http://blog.NetBSD.org/tnf/entry/revolutionizing_kernel_development_testing_with)
  151: 
  152: ### Conference publications and talks
  153: 
  154: -   "The Anykernel and Rump Kernels" gives a general overview and
  155:     demonstrates rump kernels on Windows and in Firefox. The
  156:     [video](http://video.fosdem.org/2013/maintracks/K.1.105/The_Anykernel_and_Rump_Kernels.webm),
  157:     [slides](https://fosdem.org/2013/schedule/event/operating_systems_anykernel/attachments/slides/244/export/events/attachments/operating_systems_anykernel/slides/244/fosdem2013_rumpkern.pdf)
  158:     and an
  159:     [interview](https://archive.fosdem.org/2013/interviews/2013-antii-kantee/)
  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
  163:     [paper](http://ftp.NetBSD.org/pub/NetBSD/misc/pooka/tmp/rumpdev.pdf)
  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
  169:     [paper](http://www.ukuug.org/events/eurobsdcon2009/papers/ebc09_fs-utils.pdf)
  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
  173:     [paper](http://usenix.org/events/usenix09/tech/full_papers/kantee/kantee.pdf)
  174:     and
  175:     [slides](http://usenix.org/events/usenix09/tech/slides/kantee.pdf)
  176:     are available. Presented at the 2009 USENIX Annual Technical
  177:     Conference.
  178: -   "Kernel Development in Userspace - The Rump Approach" describes
  179:     doing kernel development with rump kernels. The
  180:     [paper](http://www.bsdcan.org/2009/schedule/attachments/104_rumpdevel.pdf)
  181:     and
  182:     [slides](http://www.bsdcan.org/2009/schedule/attachments/105_bsdcan09-kantee.pdf)
  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.
  189: 
  190: ### Manual pages
  191: 
  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".
  195: 
  196: ## Discuss
  197: 
  198: Any topic related to rump kernels can be discussed on the
  199: [rumpkernel-users mailing
  200: list](https://lists.sourceforge.net/lists/listinfo/rumpkernel-users).
  201: Alternatively, you can use a NetBSD mailing which is related to a
  202: specific subtopic.
  203: 
  204: The IRC channel for rump kernels is **\#rumpkernel** on
  205: **irc.freenode.net**.
  206: 
  207: ## Availability
  208: 
  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.
  212: 
  213: ## Source Code
  214: 
  215: All of the source code is available from the NetBSD source tree and can
  216: be obtained with the usual methods.
  217: 
  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
  221: [src/lib](http://cvsweb.NetBSD.org/bsdweb.cgi/src/lib/),
  222: [src/usr.bin](http://cvsweb.NetBSD.org/bsdweb.cgi/src/usr.bin/) and
  223: [src/sys/rump](http://cvsweb.NetBSD.org/bsdweb.cgi/src/sys/rump/).

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