2008-11-20 00:58:23 +08:00
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<html>
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<body>
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<h1>User Mode Linux driver</h1>
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<p>
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The UML driver for libvirt allows use and management of paravirtualized
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guests built for User Mode Linux. UML requires no special support in
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the host kernel, so can be used by any user of any linux system, provided
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they have enough free RAM for their guest's needs, though there are
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certain restrictions on network connectivity unless the adminstrator
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has pre-created TAP devices.
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</p>
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<h2>Connections to UML driver</h2>
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<p>
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The libvirt UML driver follows the QEMU driver in providing two
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types of connection. There is one privileged instance per host,
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which runs as root. This is called the "system" instance, and allows
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full use of all host resources. Then, there is a per-user unprivileged
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"session", instance. This has more restricted capabilities, and may
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require the host administrator to setup certain resources ahead of
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time to allow full integration with the network. Example connection
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URIs are
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</p>
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2009-11-14 07:09:20 +08:00
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<pre>
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uml:///session (local access to per-user instance)
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uml+unix:///session (local access to per-user instance)
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2009-01-27 22:49:09 +08:00
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2009-11-14 07:09:20 +08:00
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uml:///system (local access to system instance)
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uml+unix:///system (local access to system instance)
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uml://example.com/system (remote access, TLS/x509)
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uml+tcp://example.com/system (remote access, SASl/Kerberos)
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uml+ssh://root@example.com/system (remote access, SSH tunnelled)
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</pre>
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2008-11-20 00:58:23 +08:00
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<h2>Example XML configuration</h2>
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<p>
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User mode Linux driver only supports directly kernel boot at
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this time. A future driver enhancement may allow a paravirt
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bootloader in a similar style to Xen's pygrub. For now though,
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the UML kernel must be stored on the host and referenced
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explicitly in the "os" element. Since UML is a paravirtualized
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technology, the kernel "type" is set to "uml"
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</p>
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<p>
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There is not yet support for networking in the driver, but
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disks can be specified in the usual libvirt manner. The main
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variation is the target device naming scheme "ubd0", and
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bus type of "uml".
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</p>
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<p>
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Once booted the primary console is connected toa PTY, and
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thus accessible with "virsh console" or equivalent tools
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</p>
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2009-11-14 07:09:20 +08:00
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<pre>
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2008-11-20 00:58:23 +08:00
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<domain type='uml'>
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<name>demo</name>
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<uuid>b4433fc2-a22e-ffb3-0a3d-9c173b395800</uuid>
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<memory>500000</memory>
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<currentMemory>500000</currentMemory>
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<vcpu>1</vcpu>
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<os>
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<type arch='x86_64'>uml</type>
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<kernel>/home/berrange/linux-uml-2.6.26-x86_64</kernel>
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</os>
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<devices>
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<disk type='file' device='disk'>
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<source file='/home/berrange/FedoraCore6-AMD64-root_fs'/>
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<target dev='ubd0' bus='uml'/>
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</disk>
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<console type='pty'/>
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</devices>
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</domain>
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2009-11-14 07:09:20 +08:00
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</pre>
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2008-11-20 00:58:23 +08:00
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</body>
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</html>
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