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Wed, 21 Jul 2021 15:25:41 +0200 (CEST) From: Markus Armbruster To: Alex =?utf-8?Q?Benn=C3=A9e?= Subject: Re: [PATCH v1 02/29] docs: collect the disparate device emulation docs into one section References: <20210720232703.10650-1-alex.bennee@linaro.org> <20210720232703.10650-3-alex.bennee@linaro.org> Date: Wed, 21 Jul 2021 15:25:41 +0200 In-Reply-To: <20210720232703.10650-3-alex.bennee@linaro.org> ("Alex =?utf-8?Q?Benn=C3=A9e=22's?= message of "Wed, 21 Jul 2021 00:26:36 +0100") Message-ID: <87bl6vbxyi.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=armbru@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=170.10.133.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -42 X-Spam_score: -4.3 X-Spam_bar: ---- X-Spam_report: (-4.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.459, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, 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: fam@euphon.net, berrange@redhat.com, Eduardo Habkost , qemu-devel@nongnu.org, f4bug@amsat.org, stefanha@redhat.com, crosa@redhat.com, pbonzini@redhat.com, aurelien@aurel32.net Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Alex Benn=C3=A9e writes: > 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 > Message-Id: <20210714182056.25888-3-alex.bennee@linaro.org> > Cc: Markus Armbruster > Cc: Paolo Bonzini > Cc: Daniel P. Berrang=C3=A9 > Cc: Eduardo Habkost > > --- > v2 > - be a bit more precise about necessity of a buses > - add an example showing id/bus relations > --- > docs/system/device-emulation.rst | 89 +++++++++++++++++++++++ > docs/system/{ =3D> devices}/ivshmem.rst | 0 > docs/system/{ =3D> devices}/net.rst | 0 > docs/system/{ =3D> devices}/nvme.rst | 0 > docs/system/{ =3D> devices}/usb.rst | 0 > docs/system/{ =3D> devices}/virtio-pmem.rst | 0 > docs/system/index.rst | 6 +- > 7 files changed, 90 insertions(+), 5 deletions(-) > create mode 100644 docs/system/device-emulation.rst > rename docs/system/{ =3D> devices}/ivshmem.rst (100%) > rename docs/system/{ =3D> devices}/net.rst (100%) > rename docs/system/{ =3D> devices}/nvme.rst (100%) > rename docs/system/{ =3D> devices}/usb.rst (100%) > rename docs/system/{ =3D> devices}/virtio-pmem.rst (100%) > > diff --git a/docs/system/device-emulation.rst b/docs/system/device-emulat= ion.rst > new file mode 100644 > index 0000000000..7af5dbefab > --- /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 PCI bus address 0 is the PCI bridge. Suggest to omit addr=3D0, or to use another, non-special PCI address. You might like addr=3D02.0 to hint at the fact that the syntax of bus addresses depends on the bus. > + > +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 Comma, I think. > +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 [...] Nothing serious, so Reviewed-by: Markus Armbruster