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From: Markus Armbruster <armbru@redhat.com>
To: "Alex Bennée" <alex.bennee@linaro.org>
Cc: fam@euphon.net, berrange@redhat.com,
	Eduardo Habkost <ehabkost@redhat.com>,
	qemu-devel@nongnu.org, f4bug@amsat.org, stefanha@redhat.com,
	crosa@redhat.com, pbonzini@redhat.com, aurelien@aurel32.net
Subject: Re: [PATCH  v1 02/29] docs: collect the disparate device emulation docs into one section
Date: Wed, 21 Jul 2021 15:25:41 +0200	[thread overview]
Message-ID: <87bl6vbxyi.fsf@dusky.pond.sub.org> (raw)
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")

Alex Bennée <alex.bennee@linaro.org> 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 Bennée <alex.bennee@linaro.org>
> Message-Id: <20210714182056.25888-3-alex.bennee@linaro.org>
> Cc: Markus Armbruster <armbru@redhat.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Daniel P. Berrangé <berrange@redhat.com>
> Cc: Eduardo Habkost <ehabkost@redhat.com>
>
> ---
> 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/{ => devices}/ivshmem.rst     |  0
>  docs/system/{ => devices}/net.rst         |  0
>  docs/system/{ => devices}/nvme.rst        |  0
>  docs/system/{ => devices}/usb.rst         |  0
>  docs/system/{ => 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/{ => devices}/ivshmem.rst (100%)
>  rename docs/system/{ => devices}/net.rst (100%)
>  rename docs/system/{ => devices}/nvme.rst (100%)
>  rename docs/system/{ => devices}/usb.rst (100%)
>  rename docs/system/{ => devices}/virtio-pmem.rst (100%)
>
> diff --git a/docs/system/device-emulation.rst b/docs/system/device-emulation.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
> +================
> +
> +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
> +============
> +
> +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=ID``) a device is attached to along with its address
> +(``addr=N``).
> +
> +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=pci.0,addr=0,id=foo
> +  --device bar,bus=foo.0,addr=1,id=baz

PCI bus address 0 is the PCI bridge.  Suggest to omit addr=0, or to use
another, non-special PCI address.  You might like addr=02.0 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
> +===============
> +
> +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
> +===================
> +
> +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 <armbru@redhat.com>



  reply	other threads:[~2021-07-21 13:39 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-20 23:26 [PATCH for 6.1-rc1 v1 00/29] various fixes pre-PR (metadata, docs, plugins, testing) Alex Bennée
2021-07-20 23:26 ` [PATCH v1 01/29] gitignore: Update with some filetypes Alex Bennée
2021-07-20 23:26 ` [PATCH v1 02/29] docs: collect the disparate device emulation docs into one section Alex Bennée
2021-07-21 13:25   ` Markus Armbruster [this message]
2021-07-20 23:26 ` [PATCH v1 03/29] docs: add a section on the generalities of vhost-user Alex Bennée
2021-07-20 23:26 ` [PATCH v1 04/29] configure: remove needless if leg Alex Bennée
2021-07-20 23:26 ` [PATCH v1 05/29] contrib/gitdm: add some new aliases to fix up commits Alex Bennée
2021-07-20 23:26 ` [PATCH v1 06/29] .mailmap: fix up some broken commit authors Alex Bennée
2021-07-20 23:26 ` [PATCH v1 07/29] contrib/gitdm: add domain-map for MontaVista Alex Bennée
2021-07-20 23:26 ` [PATCH v1 08/29] contrib/gitdm: add a group mapping for robot scanners Alex Bennée
2021-07-20 23:26 ` [PATCH v1 09/29] gitdm.config: sort the corporate GroupMap entries Alex Bennée
2021-07-21  8:06   ` Philippe Mathieu-Daudé
2021-07-20 23:26 ` [PATCH v1 10/29] contrib/gitdm: add domain-map/group-map mappings for Samsung Alex Bennée
2021-07-20 23:26 ` [PATCH v1 11/29] contrib/gitdm: add domain-map for Eldorado Alex Bennée
2021-07-20 23:26 ` [PATCH v1 12/29] contrib/gitdm: add domain-map/group-map for Wind River Alex Bennée
2021-07-20 23:26 ` [PATCH v1 13/29] contrib/gitdm: un-ironically add a mapping for LWN Alex Bennée
2021-07-20 23:26 ` [PATCH v1 14/29] contrib/gitdm: add domain-map for Crudebyte Alex Bennée
2021-07-20 23:26 ` [PATCH v1 15/29] contrib/gitdm: add domain-map for NVIDIA Alex Bennée
2021-07-20 23:26 ` [PATCH v1 16/29] contrib/gitdm: add group-map for Netflix Alex Bennée
2021-07-20 23:26 ` [PATCH v1 17/29] contrib/gitdm: add an explicit academic entry for BU Alex Bennée
2021-07-20 23:26 ` [PATCH v1 18/29] contrib/gitdm: add a new interns group-map for GSoC/Outreachy work Alex Bennée
2021-07-20 23:26 ` [PATCH v1 19/29] contrib/gitdm: add more individual contributor entries Alex Bennée
2021-07-20 23:26 ` [PATCH v1 20/29] tcg/plugins: implement a qemu_plugin_user_exit helper Alex Bennée
2021-07-20 23:26 ` [PATCH v1 21/29] plugins/cache: Fixed a bug with destroying FIFO metadata Alex Bennée
2021-07-20 23:26 ` [PATCH v1 22/29] plugins/cache: limited the scope of a mutex lock Alex Bennée
2021-07-20 23:26 ` [PATCH v1 23/29] plugins/cache: Fixed "function decl. is not a prototype" warnings Alex Bennée
2021-07-21  8:09   ` Philippe Mathieu-Daudé
2021-07-20 23:26 ` [PATCH v1 24/29] plugins: Fix physical address calculation for IO regions Alex Bennée
2021-07-20 23:26 ` [PATCH v1 25/29] hw/tricore: fix inclusion of tricore_testboard Alex Bennée
2021-08-02 16:07   ` Bastian Koppelmann
2021-07-20 23:27 ` [PATCH v1 26/29] tests/tcg/configure.sh: add handling for assembler only builds Alex Bennée
2021-07-20 23:27 ` [PATCH v1 27/29] gitlab: enable a very minimal build with the tricore container Alex Bennée
2021-07-21  7:05   ` Thomas Huth
2021-07-21 15:00   ` Willian Rampazzo
2021-07-20 23:27 ` [PATCH v1 28/29] gitlab-ci: Remove the second superfluous macos task Alex Bennée
2021-07-20 23:27 ` [PATCH v1 29/29] gitlab-ci: Extract OpenSBI job rules to reusable section Alex Bennée

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