docs: add nvme emulation documentation

Remove the docs/specs/nvme.txt and replace it with proper documentation
in docs/system/nvme.rst.

Signed-off-by: Klaus Jensen <k.jensen@samsung.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

2 files changed, 226 insertions, 0 deletions

diff --git a/docs/system/index.rst b/docs/system/index.rst
index 02d0707181..b05af716a9 100644
--- a/docs/system/index.rst
+++ b/docs/system/index.rst
@@ -23,6 +23,7 @@ Contents:
    net
    virtio-net-failover
    usb
+   nvme
    ivshmem
    linuxboot
    generic-loader
diff --git a/docs/system/nvme.rst b/docs/system/nvme.rst
new file mode 100644
index 0000000000..f7f63d6bf6
--- /dev/null
+++ b/docs/system/nvme.rst
@@ -0,0 +1,225 @@
+==============
+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.