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==============
NVMe Emulation
==============
QEMU provides NVMe emulation through the ``nvme``, ``nvme-ns`` and
``nvme-subsys`` devices.
See the following sections for specific information on
* `Adding NVMe Devices`_, `additional namespaces`_ and `NVM subsystems`_.
* Configuration of `Optional Features`_ such as `Controller Memory Buffer`_,
`Simple Copy`_, `Zoned Namespaces`_, `metadata`_ and `End-to-End Data
Protection`_,
Adding NVMe Devices
===================
Controller Emulation
--------------------
The QEMU emulated NVMe controller implements version 1.4 of the NVM Express
specification. All mandatory features are implement with a couple of exceptions
and limitations:
* Accounting numbers in the SMART/Health log page are reset when the device
is power cycled.
* Interrupt Coalescing is not supported and is disabled by default.
The simplest way to attach an NVMe controller on the QEMU PCI bus is to add the
following parameters:
.. code-block:: console
-drive file=nvm.img,if=none,id=nvm
-device nvme,serial=deadbeef,drive=nvm
There are a number of optional general parameters for the ``nvme`` device. Some
are mentioned here, but see ``-device nvme,help`` to list all possible
parameters.
``max_ioqpairs=UINT32`` (default: ``64``)
Set the maximum number of allowed I/O queue pairs. This replaces the
deprecated ``num_queues`` parameter.
``msix_qsize=UINT16`` (default: ``65``)
The number of MSI-X vectors that the device should support.
``mdts=UINT8`` (default: ``7``)
Set the Maximum Data Transfer Size of the device.
``use-intel-id`` (default: ``off``)
Since QEMU 5.2, the device uses a QEMU allocated "Red Hat" PCI Device and
Vendor ID. Set this to ``on`` to revert to the unallocated Intel ID
previously used.
Additional Namespaces
---------------------
In the simplest possible invocation sketched above, the device only support a
single namespace with the namespace identifier ``1``. To support multiple
namespaces and additional features, the ``nvme-ns`` device must be used.
.. code-block:: console
-device nvme,id=nvme-ctrl-0,serial=deadbeef
-drive file=nvm-1.img,if=none,id=nvm-1
-device nvme-ns,drive=nvm-1
-drive file=nvm-2.img,if=none,id=nvm-2
-device nvme-ns,drive=nvm-2
The namespaces defined by the ``nvme-ns`` device will attach to the most
recently defined ``nvme-bus`` that is created by the ``nvme`` device. Namespace
identifers are allocated automatically, starting from ``1``.
There are a number of parameters available:
``nsid`` (default: ``0``)
Explicitly set the namespace identifier.
``uuid`` (default: *autogenerated*)
Set the UUID of the namespace. This will be reported as a "Namespace UUID"
descriptor in the Namespace Identification Descriptor List.
``bus``
If there are more ``nvme`` devices defined, this parameter may be used to
attach the namespace to a specific ``nvme`` device (identified by an ``id``
parameter on the controller device).
NVM Subsystems
--------------
Additional features becomes available if the controller device (``nvme``) is
linked to an NVM Subsystem device (``nvme-subsys``).
The NVM Subsystem emulation allows features such as shared namespaces and
multipath I/O.
.. code-block:: console
-device nvme-subsys,id=nvme-subsys-0,nqn=subsys0
-device nvme,serial=a,subsys=nvme-subsys-0
-device nvme,serial=b,subsys=nvme-subsys-0
This will create an NVM subsystem with two controllers. Having controllers
linked to an ``nvme-subsys`` device allows additional ``nvme-ns`` parameters:
``shared`` (default: ``off``)
Specifies that the namespace will be attached to all controllers in the
subsystem. If set to ``off`` (the default), the namespace will remain a
private namespace and may only be attached to a single controller at a time.
``detached`` (default: ``off``)
If set to ``on``, the namespace will be be available in the subsystem, but
not attached to any controllers initially.
Thus, adding
.. code-block:: console
-drive file=nvm-1.img,if=none,id=nvm-1
-device nvme-ns,drive=nvm-1,nsid=1,shared=on
-drive file=nvm-2.img,if=none,id=nvm-2
-device nvme-ns,drive=nvm-2,nsid=3,detached=on
will cause NSID 1 will be a shared namespace (due to ``shared=on``) that is
initially attached to both controllers. NSID 3 will be a private namespace
(i.e. only attachable to a single controller at a time) and will not be
attached to any controller initially (due to ``detached=on``).
Optional Features
=================
Controller Memory Buffer
------------------------
``nvme`` device parameters related to the Controller Memory Buffer support:
``cmb_size_mb=UINT32`` (default: ``0``)
This adds a Controller Memory Buffer of the given size at offset zero in BAR
2.
``legacy-cmb`` (default: ``off``)
By default, the device uses the "v1.4 scheme" for the Controller Memory
Buffer support (i.e, the CMB is initially disabled and must be explicitly
enabled by the host). Set this to ``on`` to behave as a v1.3 device wrt. the
CMB.
Simple Copy
-----------
The device includes support for TP 4065 ("Simple Copy Command"). A number of
additional ``nvme-ns`` device parameters may be used to control the Copy
command limits:
``mssrl=UINT16`` (default: ``128``)
Set the Maximum Single Source Range Length (``MSSRL``). This is the maximum
number of logical blocks that may be specified in each source range.
``mcl=UINT32`` (default: ``128``)
Set the Maximum Copy Length (``MCL``). This is the maximum number of logical
blocks that may be specified in a Copy command (the total for all source
ranges).
``msrc=UINT8`` (default: ``127``)
Set the Maximum Source Range Count (``MSRC``). This is the maximum number of
source ranges that may be used in a Copy command. This is a 0's based value.
Zoned Namespaces
----------------
A namespaces may be "Zoned" as defined by TP 4053 ("Zoned Namespaces"). Set
``zoned=on`` on an ``nvme-ns`` device to configure it as a zoned namespace.
The namespace may be configured with additional parameters
``zoned.zone_size=SIZE`` (default: ``128MiB``)
Define the zone size (``ZSZE``).
``zoned.zone_capacity=SIZE`` (default: ``0``)
Define the zone capacity (``ZCAP``). If left at the default (``0``), the zone
capacity will equal the zone size.
``zoned.descr_ext_size=UINT32`` (default: ``0``)
Set the Zone Descriptor Extension Size (``ZDES``). Must be a multiple of 64
bytes.
``zoned.cross_read=BOOL`` (default: ``off``)
Set to ``on`` to allow reads to cross zone boundaries.
``zoned.max_active=UINT32`` (default: ``0``)
Set the maximum number of active resources (``MAR``). The default (``0``)
allows all zones to be active.
``zoned.max_open=UINT32`` (default: ``0``)
Set the maximum number of open resources (``MOR``). The default (``0``)
allows all zones to be open. If ``zoned.max_active`` is specified, this value
must be less than or equal to that.
Metadata
--------
The virtual namespace device supports LBA metadata in the form separate
metadata (``MPTR``-based) and extended LBAs.
``ms=UINT16`` (default: ``0``)
Defines the number of metadata bytes per LBA.
``mset=UINT8`` (default: ``0``)
Set to ``1`` to enable extended LBAs.
End-to-End Data Protection
--------------------------
The virtual namespace device supports DIF- and DIX-based protection information
(depending on ``mset``).
``pi=UINT8`` (default: ``0``)
Enable protection information of the specified type (type ``1``, ``2`` or
``3``).
``pil=UINT8`` (default: ``0``)
Controls the location of the protection information within the metadata. Set
to ``1`` to transfer protection information as the first eight bytes of
metadata. Otherwise, the protection information is transferred as the last
eight bytes.
|
