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<li class="toctree-l3"><a class="reference internal" href="#common-terms">Common Terms</a><ul>
<li class="toctree-l4"><a class="reference internal" href="#device-front-end">Device Front End</a></li>
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  <div class="section" id="device-emulation">
<span id="id1"></span><h1>Device Emulation<a class="headerlink" href="#device-emulation" title="Permalink to this headline">¶</a></h1>
<p>QEMU supports the emulation of a large number of devices from
peripherals such network cards and USB devices to integrated systems
on a chip (SoCs). Configuration of these is often a source of
confusion so it helps to have an understanding of some of the terms
used to describes devices within QEMU.</p>
<div class="section" id="common-terms">
<h2>Common Terms<a class="headerlink" href="#common-terms" title="Permalink to this headline">¶</a></h2>
<div class="section" id="device-front-end">
<h3>Device Front End<a class="headerlink" href="#device-front-end" title="Permalink to this headline">¶</a></h3>
<p>A device front end is how a device is presented to the guest. The type
of device presented should match the hardware that the guest operating
system is expecting to see. All devices can be specified with the
<code class="docutils literal notranslate"><span class="pre">--device</span></code> command line option. Running QEMU with the command line
options <code class="docutils literal notranslate"><span class="pre">--device</span> <span class="pre">help</span></code> will list all devices it is aware of. Using
the command line <code class="docutils literal notranslate"><span class="pre">--device</span> <span class="pre">foo,help</span></code> will list the additional
configuration options available for that device.</p>
<p>A front end is often paired with a back end, which describes how the
host’s resources are used in the emulation.</p>
</div>
<div class="section" id="device-buses">
<h3>Device Buses<a class="headerlink" href="#device-buses" title="Permalink to this headline">¶</a></h3>
<p>Most devices will exist on a BUS of some sort. Depending on the
machine model you choose (<code class="docutils literal notranslate"><span class="pre">-M</span> <span class="pre">foo</span></code>) a number of buses will have been
automatically created. In most cases the BUS a device is attached to
can be inferred, for example PCI devices are generally automatically
allocated to the next free address of first PCI bus found. However in
complicated configurations you can explicitly specify what bus
(<code class="docutils literal notranslate"><span class="pre">bus=ID</span></code>) a device is attached to along with its address
(<code class="docutils literal notranslate"><span class="pre">addr=N</span></code>).</p>
<p>Some devices, for example a PCI SCSI host controller, will add an
additional buses to the system that other devices can be attached to.
A hypothetical chain of devices might look like:</p>
<blockquote>
<div>–device foo,bus=pci.0,addr=0,id=foo
–device bar,bus=foo.0,addr=1,id=baz</div></blockquote>
<p>which would be a bar device (with the ID of baz) which is attached to
the first foo bus (foo.0) at address 1. The foo device which provides
that bus is itself is attached to the first PCI bus (pci.0).</p>
</div>
<div class="section" id="device-back-end">
<h3>Device Back End<a class="headerlink" href="#device-back-end" title="Permalink to this headline">¶</a></h3>
<p>The back end describes how the data from the emulated device will be
processed by QEMU. The configuration of the back end is usually
specific to the class of device being emulated. For example serial
devices will be backed by a <code class="docutils literal notranslate"><span class="pre">--chardev</span></code> which can redirect the data
to a file or socket or some other system. Storage devices are handled
by <code class="docutils literal notranslate"><span class="pre">--blockdev</span></code> which will specify how blocks are handled, for
example being stored in a qcow2 file or accessing a raw host disk
partition. Back ends can sometimes be stacked to implement features
like snapshots.</p>
<p>While the choice of back end is generally transparent to the guest,
there are cases where features will not be reported to the guest if
the back end is unable to support it.</p>
</div>
<div class="section" id="device-pass-through">
<h3>Device Pass Through<a class="headerlink" href="#device-pass-through" title="Permalink to this headline">¶</a></h3>
<p>Device pass through is where the device is actually given access to
the underlying hardware. This can be as simple as exposing a single
USB device on the host system to the guest or dedicating a video card
in a PCI slot to the exclusive use of the guest.</p>
</div>
</div>
<div class="section" id="emulated-devices">
<h2>Emulated Devices<a class="headerlink" href="#emulated-devices" title="Permalink to this headline">¶</a></h2>
<div class="toctree-wrapper compound">
<ul>
<li class="toctree-l1"><a class="reference internal" href="devices/ivshmem.html">Inter-VM Shared Memory device</a></li>
<li class="toctree-l1"><a class="reference internal" href="devices/net.html">Network emulation</a></li>
<li class="toctree-l1"><a class="reference internal" href="devices/nvme.html">NVMe Emulation</a></li>
<li class="toctree-l1"><a class="reference internal" href="devices/usb.html">USB emulation</a></li>
<li class="toctree-l1"><a class="reference internal" href="devices/vhost-user.html">vhost-user back ends</a></li>
<li class="toctree-l1"><a class="reference internal" href="devices/virtio-pmem.html">virtio pmem</a></li>
<li class="toctree-l1"><a class="reference internal" href="devices/vhost-user-rng.html">QEMU vhost-user-rng - RNG emulation</a></li>
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