device-emulation.rst (3344B)
1 .. _device-emulation: 2 3 Device Emulation 4 ---------------- 5 6 QEMU supports the emulation of a large number of devices from 7 peripherals such network cards and USB devices to integrated systems 8 on a chip (SoCs). Configuration of these is often a source of 9 confusion so it helps to have an understanding of some of the terms 10 used to describes devices within QEMU. 11 12 Common Terms 13 ~~~~~~~~~~~~ 14 15 Device Front End 16 ================ 17 18 A device front end is how a device is presented to the guest. The type 19 of device presented should match the hardware that the guest operating 20 system is expecting to see. All devices can be specified with the 21 ``--device`` command line option. Running QEMU with the command line 22 options ``--device help`` will list all devices it is aware of. Using 23 the command line ``--device foo,help`` will list the additional 24 configuration options available for that device. 25 26 A front end is often paired with a back end, which describes how the 27 host's resources are used in the emulation. 28 29 Device Buses 30 ============ 31 32 Most devices will exist on a BUS of some sort. Depending on the 33 machine model you choose (``-M foo``) a number of buses will have been 34 automatically created. In most cases the BUS a device is attached to 35 can be inferred, for example PCI devices are generally automatically 36 allocated to the next free address of first PCI bus found. However in 37 complicated configurations you can explicitly specify what bus 38 (``bus=ID``) a device is attached to along with its address 39 (``addr=N``). 40 41 Some devices, for example a PCI SCSI host controller, will add an 42 additional buses to the system that other devices can be attached to. 43 A hypothetical chain of devices might look like: 44 45 --device foo,bus=pci.0,addr=0,id=foo 46 --device bar,bus=foo.0,addr=1,id=baz 47 48 which would be a bar device (with the ID of baz) which is attached to 49 the first foo bus (foo.0) at address 1. The foo device which provides 50 that bus is itself is attached to the first PCI bus (pci.0). 51 52 53 Device Back End 54 =============== 55 56 The back end describes how the data from the emulated device will be 57 processed by QEMU. The configuration of the back end is usually 58 specific to the class of device being emulated. For example serial 59 devices will be backed by a ``--chardev`` which can redirect the data 60 to a file or socket or some other system. Storage devices are handled 61 by ``--blockdev`` which will specify how blocks are handled, for 62 example being stored in a qcow2 file or accessing a raw host disk 63 partition. Back ends can sometimes be stacked to implement features 64 like snapshots. 65 66 While the choice of back end is generally transparent to the guest, 67 there are cases where features will not be reported to the guest if 68 the back end is unable to support it. 69 70 Device Pass Through 71 =================== 72 73 Device pass through is where the device is actually given access to 74 the underlying hardware. This can be as simple as exposing a single 75 USB device on the host system to the guest or dedicating a video card 76 in a PCI slot to the exclusive use of the guest. 77 78 79 Emulated Devices 80 ~~~~~~~~~~~~~~~~ 81 82 .. toctree:: 83 :maxdepth: 1 84 85 devices/can.rst 86 devices/ccid.rst 87 devices/cxl.rst 88 devices/ivshmem.rst 89 devices/net.rst 90 devices/nvme.rst 91 devices/usb.rst 92 devices/vhost-user.rst 93 devices/virtio-pmem.rst 94 devices/vhost-user-rng.rst 95 devices/canokey.rst