f54fea113c
This commit adds basic documentation for using virtio-snd. Signed-off-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org> Reviewed-by: Alex Bennée <alex.bennee@linaro.org> Tested-by: Alex Bennée <alex.bennee@linaro.org> Message-Id: <e7fb941cf7636fdff40cbdcdcd660dec5f15ca3c.1698062525.git.manos.pitsidianakis@linaro.org> Acked-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
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.. _device-emulation:
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Device Emulation
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----------------
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QEMU supports the emulation of a large number of devices from
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peripherals such network cards and USB devices to integrated systems
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on a chip (SoCs). Configuration of these is often a source of
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confusion so it helps to have an understanding of some of the terms
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used to describes devices within QEMU.
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Common Terms
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~~~~~~~~~~~~
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Device Front End
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================
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A device front end is how a device is presented to the guest. The type
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of device presented should match the hardware that the guest operating
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system is expecting to see. All devices can be specified with the
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``--device`` command line option. Running QEMU with the command line
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options ``--device help`` will list all devices it is aware of. Using
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the command line ``--device foo,help`` will list the additional
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configuration options available for that device.
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A front end is often paired with a back end, which describes how the
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host's resources are used in the emulation.
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Device Buses
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============
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Most devices will exist on a BUS of some sort. Depending on the
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machine model you choose (``-M foo``) a number of buses will have been
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automatically created. In most cases the BUS a device is attached to
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can be inferred, for example PCI devices are generally automatically
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allocated to the next free address of first PCI bus found. However in
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complicated configurations you can explicitly specify what bus
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(``bus=ID``) a device is attached to along with its address
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(``addr=N``).
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Some devices, for example a PCI SCSI host controller, will add an
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additional buses to the system that other devices can be attached to.
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A hypothetical chain of devices might look like:
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--device foo,bus=pci.0,addr=0,id=foo
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--device bar,bus=foo.0,addr=1,id=baz
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which would be a bar device (with the ID of baz) which is attached to
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the first foo bus (foo.0) at address 1. The foo device which provides
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that bus is itself is attached to the first PCI bus (pci.0).
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Device Back End
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===============
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The back end describes how the data from the emulated device will be
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processed by QEMU. The configuration of the back end is usually
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specific to the class of device being emulated. For example serial
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devices will be backed by a ``--chardev`` which can redirect the data
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to a file or socket or some other system. Storage devices are handled
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by ``--blockdev`` which will specify how blocks are handled, for
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example being stored in a qcow2 file or accessing a raw host disk
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partition. Back ends can sometimes be stacked to implement features
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like snapshots.
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While the choice of back end is generally transparent to the guest,
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there are cases where features will not be reported to the guest if
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the back end is unable to support it.
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Device Pass Through
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===================
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Device pass through is where the device is actually given access to
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the underlying hardware. This can be as simple as exposing a single
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USB device on the host system to the guest or dedicating a video card
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in a PCI slot to the exclusive use of the guest.
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Emulated Devices
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~~~~~~~~~~~~~~~~
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.. toctree::
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:maxdepth: 1
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devices/can.rst
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devices/ccid.rst
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devices/cxl.rst
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devices/ivshmem.rst
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devices/keyboard.rst
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devices/net.rst
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devices/nvme.rst
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devices/usb.rst
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devices/vhost-user.rst
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devices/virtio-gpu.rst
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devices/virtio-pmem.rst
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devices/virtio-snd.rst
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devices/vhost-user-rng.rst
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devices/canokey.rst
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devices/usb-u2f.rst
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devices/igb.rst
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