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+[[meta copyright="Copyright © 2008, 2009 Free Software Foundation, Inc."]]
+
+[[meta license="""[[toggle id="license" text="GFDL 1.2+"]][[toggleable
+id="license" text="Permission is granted to copy, distribute and/or modify this
+document under the terms of the GNU Free Documentation License, Version 1.2 or
+any later version published by the Free Software Foundation; with no Invariant
+Sections, no Front-Cover Texts, and no Back-Cover Texts.  A copy of the license
+is included in the section entitled
+[[GNU_Free_Documentation_License|/fdl]]."]]"""]]
+
+[[meta title="Virtualization Using Hurd Mechanisms"]]
+
+The main idea behind the Hurd design is to allow users to replace almost any
+system functionality ([[extensible_system|extensibility]]). Any user can easily
+create a subenvironment using some custom [[servers|hurd/translator]] instead
+of the default system servers. This can be seen as an
+[[advanced_lightweight_virtualization|hurd/virtualization]] mechanism, which
+allows implementing all kinds of standard and nonstandard virtualization
+scenarios.
+
+However, though the basic mechanisms are there, currently it's not easy to make
+use of these possibilities, because we lack tools to automatically launch the
+desired constellations.
+
+The goal is to create a set of powerful tools for managing at least one
+desirable virtualization scenario. One possible starting point could be the
+[[hurd/subhurd]]/[[hurd/neighborhurd]] mechanism, which allows a second almost totally
+independant instance of the Hurd in parallel to the main one. The current
+implementation has serious limitations though. A subhurd can only be started by
+root. There are no communication channels between the subhurd and the main one.
+There is no mechanism for safe sharing of hardware devices. Fixing this issues
+could turn subhurds into a very powerful solution for lightweight
+virtualization using so-called logical partitions. (Similar to Linux-vserver,
+OpenVZ etc.)
+
+While subhurd allow creating a complete second system instance, with an own set
+of Hurd servers and [[UNIX]] daemons and all, there are also situations where it is
+desirable to have a smaller subenvironment, living withing the main system and
+using most of its facilities -- similar to a chroot environment. A simple way
+to create such a subenvironment with a single command would be very helpful.
+
+It might be possible to implement (perhaps as a prototype) a wrapper using
+existing tools (chroot and [[hurd/translator/unionfs]]); or it might require more specific tools,
+like some kind of unionfs-like filesytem proxy that mirrors other parts of the
+filesystem, but allows overriding individual locations, in conjuction with
+either chroot or some similar mechanism to create a subenvironment with a
+different root filesystem.
+
+It's also desirable to have a mechanism allowing a user to set up such a custom
+environment in a way that it will automatically get launched on login --
+practically allowing the user to run a customized operating system in his own
+account.
+
+Yet another interesting scenario would be a subenvironment -- using some kind
+of special filesystem proxy again -- in which the user serves as root, being
+able to create local sub-users and/or sub-groups.
+
+This would allow the user to run "dangerous" applications (webbrowser, chat
+client etc.) in a confined fashion, allowing it access to only a subset of the
+user's files and other resources. (This could be done either using a lot of
+groups for individual resources, and lots of users for individual applications;
+adding a user to a group would give the corresponding application access to the
+corresponding resource -- an advanced [[ACL]] mechanism. Or leave out the groups,
+assigning the resources to users instead, and use the Hurd's ability for a
+process to have multiple user IDs, to equip individual applications with sets
+of user IDs giving them access to the necessary resources -- basically a
+[[capability]] mechanism.)
+
+The student will have to pick (at least) one of the described scenarios -- or
+come up with some other one in a similar spirit -- and implement all the tools
+(scripts, translators) necessary to make it available to users in an
+easy-to-use fashion. While the Hurd by default already offers the necessary
+mechanisms for that, these are not perfect and could be further refined for
+even better virtualization capabilities. Should need or desire for specific
+improvements in that regard come up in the course of this project, implementing
+these improvements can be considered part of the task.
+
+Completing this project will require gaining a very good understanding of the
+Hurd architecture and spirit. Previous experience with other virtualization
+solutions would be very helpful.
+
+Possible mentors: Olaf Buddenhagen (antrik)
+
+Exercise: Make some modification to the "boot" programm used to start subhurds.
+(More specific suggestions welcome... :-) )
+
+*Status*: Zheng da has has implemented [[network_virtualization|zhengda]] (an
+important prerequisite for unprivileged subhurds) for GSoC 2008, along with
+various other interesting bits, including a mechanism to override socket
+servers; a proc proxy that allows running processes/subenvironments with a
+pseudo device master port; and a mechanism to pass arbitrary virtual devices to
+a subhurd. He is still working on running subhurds by normal users.