Start splitting out part of <devices> into smaller sections. Signed-off-by: Peter Krempa <pkrempa@xxxxxxxxxx> --- docs/formatdomain-devices-virtio.rst | 59 +++++++++++++++++++++++++++ docs/formatdomain-devices.rst | 61 +--------------------------- docs/meson.build | 1 + 3 files changed, 61 insertions(+), 60 deletions(-) create mode 100644 docs/formatdomain-devices-virtio.rst diff --git a/docs/formatdomain-devices-virtio.rst b/docs/formatdomain-devices-virtio.rst new file mode 100644 index 0000000000..21a0603984 --- /dev/null +++ b/docs/formatdomain-devices-virtio.rst @@ -0,0 +1,59 @@ +:anchor:`<a id="elementsVirtio"/>` + +Virtio-related options +~~~~~~~~~~~~~~~~~~~~~~ + +QEMU's virtio devices have some attributes related to the virtio transport under +the ``driver`` element: The ``iommu`` attribute enables the use of emulated +IOMMU by the device. The attribute ``ats`` controls the Address Translation +Service support for PCIe devices. This is needed to make use of IOTLB support +(see `IOMMU device <#elementsIommu>`__). Possible values are ``on`` or ``off``. +:since:`Since 3.5.0` + +The attribute ``packed`` controls if QEMU should try to use packed virtqueues. +Compared to regular split queues, packed queues consist of only a single +descriptor ring replacing available and used ring, index and descriptor buffer. +This can result in better cache utilization and performance. If packed +virtqueues are actually used depends on the feature negotiation between QEMU, +vhost backends and guest drivers. Possible values are ``on`` or ``off``. +:since:`Since 6.3.0 (QEMU and KVM only)` + +:anchor:`<a id="elementsVirtioTransitional"/>` + +Virtio transitional devices +~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +:since:`Since 5.2.0` , some of QEMU's virtio devices, when used with PCI/PCIe +machine types, accept the following ``model`` values: + +``virtio-transitional`` + This device can work both with virtio 0.9 and virtio 1.0 guest drivers, so + it's the best choice when compatibility with older guest operating systems is + desired. libvirt will plug the device into a conventional PCI slot. +``virtio-non-transitional`` + This device can only work with virtio 1.0 guest drivers, and it's the + recommended option unless compatibility with older guest operating systems is + necessary. libvirt will plug the device into either a PCI Express slot or a + conventional PCI slot based on the machine type, resulting in a more + optimized PCI topology. +``virtio`` + This device will work like a ``virtio-non-transitional`` device when plugged + into a PCI Express slot, and like a ``virtio-transitional`` device otherwise; + libvirt will pick one or the other based on the machine type. This is the + best choice when compatibility with libvirt versions older than 5.2.0 is + necessary, but it's otherwise not recommended to use it. + +While the information outlined above applies to most virtio devices, there are a +few exceptions: + +- for SCSI controllers, ``virtio-scsi`` must be used instead of ``virtio`` for + backwards compatibility reasons; +- some devices, such as GPUs and input devices (keyboard, tablet and mouse), + are only defined in the virtio 1.0 spec and as such don't have a transitional + variant: the only accepted model is ``virtio``, which will result in a + non-transitional device. + +For more details see the `qemu patch +posting <https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg00923.html>`__ +and the `virtio-1.0 +spec <http://docs.oasis-open.org/virtio/virtio/v1.0/virtio-v1.0.html>`__. diff --git a/docs/formatdomain-devices.rst b/docs/formatdomain-devices.rst index c789495e5d..16be7883b6 100644 --- a/docs/formatdomain-devices.rst +++ b/docs/formatdomain-devices.rst @@ -42,66 +42,7 @@ following characters: ``[a-zA-Z0-9_-]``. :since:`Since 3.9.0` .. include:: formatdomain-devices-disk.rst .. include:: formatdomain-devices-filesystem.rst .. include:: formatdomain-devices-address.rst - -:anchor:`<a id="elementsVirtio"/>` - -Virtio-related options -~~~~~~~~~~~~~~~~~~~~~~ - -QEMU's virtio devices have some attributes related to the virtio transport under -the ``driver`` element: The ``iommu`` attribute enables the use of emulated -IOMMU by the device. The attribute ``ats`` controls the Address Translation -Service support for PCIe devices. This is needed to make use of IOTLB support -(see `IOMMU device <#elementsIommu>`__). Possible values are ``on`` or ``off``. -:since:`Since 3.5.0` - -The attribute ``packed`` controls if QEMU should try to use packed virtqueues. -Compared to regular split queues, packed queues consist of only a single -descriptor ring replacing available and used ring, index and descriptor buffer. -This can result in better cache utilization and performance. If packed -virtqueues are actually used depends on the feature negotiation between QEMU, -vhost backends and guest drivers. Possible values are ``on`` or ``off``. -:since:`Since 6.3.0 (QEMU and KVM only)` - -:anchor:`<a id="elementsVirtioTransitional"/>` - -Virtio transitional devices -~~~~~~~~~~~~~~~~~~~~~~~~~~~ - -:since:`Since 5.2.0` , some of QEMU's virtio devices, when used with PCI/PCIe -machine types, accept the following ``model`` values: - -``virtio-transitional`` - This device can work both with virtio 0.9 and virtio 1.0 guest drivers, so - it's the best choice when compatibility with older guest operating systems is - desired. libvirt will plug the device into a conventional PCI slot. -``virtio-non-transitional`` - This device can only work with virtio 1.0 guest drivers, and it's the - recommended option unless compatibility with older guest operating systems is - necessary. libvirt will plug the device into either a PCI Express slot or a - conventional PCI slot based on the machine type, resulting in a more - optimized PCI topology. -``virtio`` - This device will work like a ``virtio-non-transitional`` device when plugged - into a PCI Express slot, and like a ``virtio-transitional`` device otherwise; - libvirt will pick one or the other based on the machine type. This is the - best choice when compatibility with libvirt versions older than 5.2.0 is - necessary, but it's otherwise not recommended to use it. - -While the information outlined above applies to most virtio devices, there are a -few exceptions: - -- for SCSI controllers, ``virtio-scsi`` must be used instead of ``virtio`` for - backwards compatibility reasons; -- some devices, such as GPUs and input devices (keyboard, tablet and mouse), - are only defined in the virtio 1.0 spec and as such don't have a transitional - variant: the only accepted model is ``virtio``, which will result in a - non-transitional device. - -For more details see the `qemu patch -posting <https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg00923.html>`__ -and the `virtio-1.0 -spec <http://docs.oasis-open.org/virtio/virtio/v1.0/virtio-v1.0.html>`__. +.. include:: formatdomain-devices-virtio.rst :anchor:`<a id="elementsControllers"/>` diff --git a/docs/meson.build b/docs/meson.build index e30f213739..f7c8f12579 100644 --- a/docs/meson.build +++ b/docs/meson.build @@ -127,6 +127,7 @@ docs_rst_files = [ 'formatdomain-devices-disk.rst', 'formatdomain-devices-filesystem.rst', 'formatdomain-devices-address.rst', + 'formatdomain-devices-virtio.rst', ] }, { 'name': 'hacking' }, -- 2.26.2
