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Dynamic Uml Mesh Modeler » History » Version 27

Andreas Steffen, 19.07.2011 15:44
get UML guest kernel from linux-dumm git repository

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h1. Dynamic Uml Mesh Modeler
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_Dumm_ is a framework to set up a virtual network using user mode linux guests.
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It cleverly glues together some nice technologies to build networks dynamically.
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To change the network topology, hosts are not required to reboot, changes apply
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instantly and configuration can be done on the host (no network connection
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required to change anything).
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h2. Status
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_Dumm_ is experimental and in development (see source:src/dumm). 
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Along with the _dumm_ library, two frontends are currently usable:
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* A graphical GTK client
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* A console client with Ruby bindings to script scenarios in Ruby
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The graphical client is incomplete. It is missing:
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* Removal of added switches
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* Disconnecting guests from switches
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* Scenario management
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The Ruby console client also misses a surrounding testing infrastructure which
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will be built with ruby in the near future.
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h2. Why UML?
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UML is a senior in vitualization technologies, and there is a lot of new
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hyped stuff about virtualization around. However, UML is lightweight, easy to
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set up and allows dynamic reconfiguration (e.g. add/remove interfaces at
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runtime), allows access to the hosts filesystem through hostfs and has some
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other neat features.
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Performance is not critical for our needs, and maybe we get hardware
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virtualization support soon in UML.
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It is free and fits perfectly.
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h2. Requirements
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* Host:
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** Kernel:
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*** A recent 2.6 kernel
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*** "SKAS3 patch":http://www.user-mode-linux.org/~blaisorblade/patches/skas3-2.6/ recommended
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*** "FUSE":http://fuse.sourceforge.net/ enabled
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*** support for TAP devices
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** Userland:
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*** [[libstrongswan]]
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*** libbridge from "bridge-utils":http://linux-net.osdl.org/index.php/Bridge
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*** using the GTK client:
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**** GTK+2 with developement headers
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**** Gnome VteTerminal with developement headers
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*** using the Ruby client:
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**** Ruby 1.8 with developement headers
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**** IRB
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* Guest:
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** Kernel:
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*** hostfs
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*** tuntap networking
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*** our extended mconsole exec patch (see source:src/dumm/patches)
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** Userland:
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*** ip from iproute2
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h2. Architecture
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h3. Working set
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Dumm needs a directory to store all its files, guest configurations and other
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stuff. Inside that working directory, you'll find:
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<pre>
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workingdir/      - root folder containing a set of hosts and scenarios
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  guests/        - contains all created guests
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    alice/       - subdirectory for host "alice"
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      alice/     - UML created folder (named umid) containing UML runtime files
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      args       - additional arguments to pass to guest, such as memory configuration
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      pid        - PID file if guest is running, handy to attach gdb to kernel
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      linux      - symlinked UML kernel this host uses
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      master/    - symlinked master root file system for this host
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      diff/      - copy-on-write overlay to master this host uses
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      union/     - mounted unified filesystem (master + diff + optional scenario)
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    bob/
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      ...        - same stuff as in alice
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  templates/     - contains all scenario templates
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    test1/       - a scenario folder
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      diff/      - copy-on-write overlays for each guest's union folder
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        alice/   - COW for alice
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        bob/     - COW for bob
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</pre>
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h3. Networking
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Network connectivity is realized through tap devices. When creating a _eth0_
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network device on _alice_, a _alice-eth0_ tap device appears on the host. These
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are directly connected, when _alice_ sends traffic to _eth0_, it appears on the
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host at _alice-eth0_. You can see that as a small network segment (or just a
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cable), where these interfaces are attached directly.
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To build larger network segments, linux bridging on the host comes into play.
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Segments are created by creating a bridge (as with brctl), and then attaching
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our tap devices to that bridge. Routing can be done on a UML guest, or even on
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the host.
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This setup has some advantages over the _uml_switch_ solution. Bridging works
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more reliable in the kernel, and as we see every network interface on the host,
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we can sniff at every interface to get some clue what the guests are doing.
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h2. HowTo
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In this mini-howto, we build and boot a minimalistic debian guest on a ubuntu host.
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We do everything as root here to simplify things!
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h3. Host setup
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* Install required packages: <pre>
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apt-get install libfuse-dev libgtk2.0-dev libvte-dev ruby1.8-dev irb1.8
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</pre>
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* Install libbridge manually: <pre>
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git clone git://git.kernel.org/pub/scm/linux/kernel/git/shemminger/bridge-utils.git
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cd bridge-utils
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autoconf
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./configure
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cd libbridge
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gcc -fPIC -c libbridge_devif.c libbridge_if.c libbridge_init.c libbridge_misc.c
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ar rcs libbridge.a libbridge_devif.o libbridge_if.o libbridge_init.o libbridge_misc.o
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ranlib libbridge.a
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install libbridge.a /usr/local/lib
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install libbridge.h /usr/local/include
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</pre>
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* Build and install strongSwan from Git sources: <pre>
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git clone http://git.strongswan.org/strongswan.git
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cd strongswan
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less HACKING
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./autogen
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./configure --enable-dumm [other options]
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make
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make install
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</pre>
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* Ubuntu kernels almost fit our needs, they have FUSE and TAP device support. However, SKAS3 mode is missing. Build your own kernel based on the "Ubuntu Howto":https://wiki.ubuntu.com/KernelCustomBuild, patched with the "SKAS3 patch":http://www.user-mode-linux.org/~blaisorblade/patches/skas3-2.6/. SKAS3 is not required, but guests run much faster with SKAS3 enabled on the host.
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h3. Guest master filesystem setup
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* Create a clean directory and a directory for our master filesystem in it: <pre>
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mkdir umldir
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cd umldir
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mkdir master
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</pre>
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* Bootstrap a debian sid system into master: <pre>
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debootstrap sid master http://mirror.switch.ch/ftp/pub/debian/
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</pre>To build a x86 guest on a x64 host, use the --arch option.
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* Enter chroot <pre>
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chroot master
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</pre>
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* Enable main repository <pre>
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echo deb http://mirror.switch.ch/ftp/pub/debian sid main contrib > /etc/apt/sources.list
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apt-get update
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</pre>
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* Install proper locales support <pre>
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apt-get install locales
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dpkg-reconfigure locales
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</pre>
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* For Ubuntu lucid guests, you'll have to specify the locales before generating them: <pre>
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echo "en_US.UTF-8 UTF-8" >> /var/lib/locales/supported.d/local
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</pre>
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* Install some packages for strongSwan <pre>
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apt-get install libgmp3c2 libsqlite3-0 libcurl3 dropbear gdb binutils
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</pre>
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* Leave chroot <pre>
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exit
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</pre>
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* Build a UML guest kernel: <pre>
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git clone git://git.strongswan.org/linux-dumm.git
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cd linux-dumm
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git checkout -b uml-ha-2.6.39 uml-ha-2.6.39
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wget http://download.strongswan.org/uml/config-2.6.39
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mv config-2.6.39 .config
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make linux ARCH=um SUBARCH=i386
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</pre>
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h3. Start a network
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You'll have to run the tools as root. Make sure you have a DISPLAY set, e.g. by starting it under _sudo_.
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* Invoke the graphical client <pre>
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sudo ipsec dumm
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</pre>
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Add guests, select our master filesystem and the compiled kernel. Add a bridges and connect your guests to it.
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Start your guests and configure them. 
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* Using the _irdumm_ ruby client <pre>
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sudo ipsec irdumm
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irb> sun = Guest.new("sun", "path/to/linux-2.6.27/linux", "path/to/master/", "mem=64M con1=xterm")
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irb> sun.start
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irb> sun.exec("echo sun > /etc/hostname")
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irb> sun.add("eth0").connect(Bridge.new("br0")).add("192.168.0.1")
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irb> sun.exec("ifconfig") { |line| puts line }
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irb> quit
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</pre>
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h2. Installing strongSwan on guests
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As we have full access to the master filesystem on the host, we can build strongSwan on the host and install it to the guests
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<pre>
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cd path/to/strongswan/
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DESTDIR=/full/path/to/master make install
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</pre>
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h2. Troubleshooting
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h3. The kernel cant find _init_, but it's there!?
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Double check you are using the same architecture for kernel and filesystem. A i386 kernel can't boot a x64 init, and it currently does not work vice-versa, either. Pass the ARCH/SUBARCH variables after _make_, otherwise they get ignored!
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h3. Debugging with gdb inside a x64 UML guest fails with an Input/Output error!
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This is a known issue, but has not yet been solved.
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h3. I'm using a maverick i386 guest on a x64 host, but condition variables behave strangely.
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This is a known issue, somehow related to eglibc version. Threads waiting in condvars don't get
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wakened up while signaled. Not yet solved.
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h3. Unix sockets created in the guest through hostfs are inaccessible in the guest.
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Looks like an issue with hostfs, not yet solved. Creating Unix Sockets on an in-guest mounted tmpfs should work.