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charset="utf-8" Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=2a00:1450:4864:20::430; envelope-from=alex.bennee@linaro.org; helo=mail-wr1-x430.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: =?UTF-8?q?Daniel=20P=20=2E=20Berrang=C3=A9?= , Eduardo Habkost , qemu-devel@nongnu.org, Markus Armbruster , Paolo Bonzini , =?UTF-8?q?Alex=20Benn=C3=A9e?= Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: fail (Header signature does not verify) X-ZM-MESSAGEID: 1627060253697100001 While we are at it add a brief preamble that explains some of the common concepts in QEMU's device emulation which will hopefully lead to less confusing about our dizzying command line options. Signed-off-by: Alex Benn=C3=A9e Reviewed-by: Markus Armbruster Cc: Paolo Bonzini Cc: Daniel P. Berrang=C3=A9 Cc: Eduardo Habkost Message-Id: <20210720232703.10650-3-alex.bennee@linaro.org> diff --git a/docs/system/device-emulation.rst b/docs/system/device-emulatio= n.rst new file mode 100644 index 0000000000..8adf05f606 --- /dev/null +++ b/docs/system/device-emulation.rst @@ -0,0 +1,89 @@ +.. _device-emulation: + +Device Emulation +---------------- + +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. + +Common Terms +~~~~~~~~~~~~ + +Device Front End +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D + +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 +``--device`` command line option. Running QEMU with the command line +options ``--device help`` will list all devices it is aware of. Using +the command line ``--device foo,help`` will list the additional +configuration options available for that device. + +A front end is often paired with a back end, which describes how the +host's resources are used in the emulation. + +Device Buses +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D + +Most devices will exist on a BUS of some sort. Depending on the +machine model you choose (``-M foo``) 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 +(``bus=3DID``) a device is attached to along with its address +(``addr=3DN``). + +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: + + --device foo,bus=3Dpci.0,addr=3D0,id=3Dfoo + --device bar,bus=3Dfoo.0,addr=3D1,id=3Dbaz + +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). + + +Device Back End +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D + +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 ``--chardev`` which can redirect the data +to a file or socket or some other system. Storage devices are handled +by ``--blockdev`` 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. + +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. + +Device Pass Through +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D + +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. + + +Emulated Devices +~~~~~~~~~~~~~~~~ + +.. toctree:: + :maxdepth: 1 + + devices/ivshmem.rst + devices/net.rst + devices/nvme.rst + devices/usb.rst + devices/virtio-pmem.rst diff --git a/docs/system/ivshmem.rst b/docs/system/devices/ivshmem.rst similarity index 100% rename from docs/system/ivshmem.rst rename to docs/system/devices/ivshmem.rst diff --git a/docs/system/net.rst b/docs/system/devices/net.rst similarity index 100% rename from docs/system/net.rst rename to docs/system/devices/net.rst diff --git a/docs/system/nvme.rst b/docs/system/devices/nvme.rst similarity index 100% rename from docs/system/nvme.rst rename to docs/system/devices/nvme.rst diff --git a/docs/system/usb.rst b/docs/system/devices/usb.rst similarity index 100% rename from docs/system/usb.rst rename to docs/system/devices/usb.rst diff --git a/docs/system/virtio-pmem.rst b/docs/system/devices/virtio-pmem.= rst similarity index 100% rename from docs/system/virtio-pmem.rst rename to docs/system/devices/virtio-pmem.rst diff --git a/docs/system/index.rst b/docs/system/index.rst index fda4b1b705..64a424ae99 100644 --- a/docs/system/index.rst +++ b/docs/system/index.rst @@ -11,15 +11,12 @@ or Hypervisor.Framework. =20 quickstart invocation + device-emulation keys mux-chardev monitor images - net virtio-net-failover - usb - nvme - ivshmem linuxboot generic-loader guest-loader @@ -30,7 +27,6 @@ or Hypervisor.Framework. gdb managed-startup cpu-hotplug - virtio-pmem pr-manager targets security --=20 2.20.1