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-
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-
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-
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- OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+.. SPDX-License-Identifier: BSD-3-Clause
+ Copyright(c) 2010-2016 Intel Corporation.
Vhost Library
=============
-The vhost library implements a user space vhost driver. It supports both vhost-cuse
-(cuse: user space character device) and vhost-user(user space socket server).
-It also creates, manages and destroys vhost devices for corresponding virtio
-devices in the guest. Vhost supported vSwitch could register callbacks to this
-library, which will be called when a vhost device is activated or deactivated
-by guest virtual machine.
+The vhost library implements a user space virtio net server allowing the user
+to manipulate the virtio ring directly. In another words, it allows the user
+to fetch/put packets from/to the VM virtio net device. To achieve this, a
+vhost library should be able to:
+
+* Access the guest memory:
+
+ For QEMU, this is done by using the ``-object memory-backend-file,share=on,...``
+ option. Which means QEMU will create a file to serve as the guest RAM.
+ The ``share=on`` option allows another process to map that file, which
+ means it can access the guest RAM.
+
+* Know all the necessary information about the vring:
+
+ Information such as where the available ring is stored. Vhost defines some
+ messages (passed through a Unix domain socket file) to tell the backend all
+ the information it needs to know how to manipulate the vring.
+
Vhost API Overview
------------------
-* Vhost driver registration
+The following is an overview of some key Vhost API functions:
+
+* ``rte_vhost_driver_register(path, flags)``
+
+ This function registers a vhost driver into the system. ``path`` specifies
+ the Unix domain socket file path.
+
+ Currently supported flags are:
+
+ - ``RTE_VHOST_USER_CLIENT``
+
+ DPDK vhost-user will act as the client when this flag is given. See below
+ for an explanation.
+
+ - ``RTE_VHOST_USER_NO_RECONNECT``
+
+ When DPDK vhost-user acts as the client it will keep trying to reconnect
+ to the server (QEMU) until it succeeds. This is useful in two cases:
+
+ * When QEMU is not started yet.
+ * When QEMU restarts (for example due to a guest OS reboot).
+
+ This reconnect option is enabled by default. However, it can be turned off
+ by setting this flag.
+
+ - ``RTE_VHOST_USER_IOMMU_SUPPORT``
+
+ IOMMU support will be enabled when this flag is set. It is disabled by
+ default.
+
+ Enabling this flag makes possible to use guest vIOMMU to protect vhost
+ from accessing memory the virtio device isn't allowed to, when the feature
+ is negotiated and an IOMMU device is declared.
+
+ - ``RTE_VHOST_USER_POSTCOPY_SUPPORT``
+
+ Postcopy live-migration support will be enabled when this flag is set.
+ It is disabled by default.
+
+ Enabling this flag should only be done when the calling application does
+ not pre-fault the guest shared memory, otherwise migration would fail.
+
+ - ``RTE_VHOST_USER_LINEARBUF_SUPPORT``
+
+ Enabling this flag forces vhost dequeue function to only provide linear
+ pktmbuf (no multi-segmented pktmbuf).
+
+ The vhost library by default provides a single pktmbuf for given a
+ packet, but if for some reason the data doesn't fit into a single
+ pktmbuf (e.g., TSO is enabled), the library will allocate additional
+ pktmbufs from the same mempool and chain them together to create a
+ multi-segmented pktmbuf.
+
+ However, the vhost application needs to support multi-segmented format.
+ If the vhost application does not support that format and requires large
+ buffers to be dequeue, this flag should be enabled to force only linear
+ buffers (see RTE_VHOST_USER_EXTBUF_SUPPORT) or drop the packet.
+
+ It is disabled by default.
+
+ - ``RTE_VHOST_USER_EXTBUF_SUPPORT``
+
+ Enabling this flag allows vhost dequeue function to allocate and attach
+ an external buffer to a pktmbuf if the pkmbuf doesn't provide enough
+ space to store all data.
+
+ This is useful when the vhost application wants to support large packets
+ but doesn't want to increase the default mempool object size nor to
+ support multi-segmented mbufs (non-linear). In this case, a fresh buffer
+ is allocated using rte_malloc() which gets attached to a pktmbuf using
+ rte_pktmbuf_attach_extbuf().
+
+ See RTE_VHOST_USER_LINEARBUF_SUPPORT as well to disable multi-segmented
+ mbufs for application that doesn't support chained mbufs.
+
+ It is disabled by default.
+
+ - ``RTE_VHOST_USER_ASYNC_COPY``
+
+ Asynchronous data path will be enabled when this flag is set. Async data
+ path allows applications to register async copy devices (typically
+ hardware DMA channels) to the vhost queues. Vhost leverages the copy
+ device registered to free CPU from memory copy operations. A set of
+ async data path APIs are defined for DPDK applications to make use of
+ the async capability. Only packets enqueued/dequeued by async APIs are
+ processed through the async data path.
+
+ Currently this feature is only implemented on split ring enqueue data
+ path.
+
+ It is disabled by default.
+
+ - ``RTE_VHOST_USER_NET_COMPLIANT_OL_FLAGS``
+
+ Since v16.04, the vhost library forwards checksum and gso requests for
+ packets received from a virtio driver by filling Tx offload metadata in
+ the mbuf. This behavior is inconsistent with other drivers but it is left
+ untouched for existing applications that might rely on it.
+
+ This flag disables the legacy behavior and instead ask vhost to simply
+ populate Rx offload metadata in the mbuf.
+
+ It is disabled by default.
+
+* ``rte_vhost_driver_set_features(path, features)``
+
+ This function sets the feature bits the vhost-user driver supports. The
+ vhost-user driver could be vhost-user net, yet it could be something else,
+ say, vhost-user SCSI.
+
+* ``rte_vhost_driver_callback_register(path, vhost_device_ops)``
+
+ This function registers a set of callbacks, to let DPDK applications take
+ the appropriate action when some events happen. The following events are
+ currently supported:
+
+ * ``new_device(int vid)``
+
+ This callback is invoked when a virtio device becomes ready. ``vid``
+ is the vhost device ID.
+
+ * ``destroy_device(int vid)``
+
+ This callback is invoked when a virtio device is paused or shut down.
+
+ * ``vring_state_changed(int vid, uint16_t queue_id, int enable)``
+
+ This callback is invoked when a specific queue's state is changed, for
+ example to enabled or disabled.
+
+ * ``features_changed(int vid, uint64_t features)``
+
+ This callback is invoked when the features is changed. For example,
+ ``VHOST_F_LOG_ALL`` will be set/cleared at the start/end of live
+ migration, respectively.
+
+ * ``new_connection(int vid)``
+
+ This callback is invoked on new vhost-user socket connection. If DPDK
+ acts as the server the device should not be deleted before
+ ``destroy_connection`` callback is received.
+
+ * ``destroy_connection(int vid)``
+
+ This callback is invoked when vhost-user socket connection is closed.
+ It indicates that device with id ``vid`` is no longer in use and can be
+ safely deleted.
+
+* ``rte_vhost_driver_disable/enable_features(path, features))``
+
+ This function disables/enables some features. For example, it can be used to
+ disable mergeable buffers and TSO features, which both are enabled by
+ default.
+
+* ``rte_vhost_driver_start(path)``
+
+ This function triggers the vhost-user negotiation. It should be invoked at
+ the end of initializing a vhost-user driver.
+
+* ``rte_vhost_enqueue_burst(vid, queue_id, pkts, count)``
+
+ Transmits (enqueues) ``count`` packets from host to guest.
+
+* ``rte_vhost_dequeue_burst(vid, queue_id, mbuf_pool, pkts, count)``
+
+ Receives (dequeues) ``count`` packets from guest, and stored them at ``pkts``.
+
+* ``rte_vhost_crypto_create(vid, cryptodev_id, sess_mempool, socket_id)``
+
+ As an extension of new_device(), this function adds virtio-crypto workload
+ acceleration capability to the device. All crypto workload is processed by
+ DPDK cryptodev with the device ID of ``cryptodev_id``.
+
+* ``rte_vhost_crypto_free(vid)``
- rte_vhost_driver_register registers the vhost driver into the system.
- For vhost-cuse, character device file will be created under the /dev directory.
- Character device name is specified as the parameter.
- For vhost-user, a unix domain socket server will be created with the parameter as
- the local socket path.
+ Frees the memory and vhost-user message handlers created in
+ rte_vhost_crypto_create().
-* Vhost session start
+* ``rte_vhost_crypto_fetch_requests(vid, queue_id, ops, nb_ops)``
- rte_vhost_driver_session_start starts the vhost session loop.
- Vhost session is an infinite blocking loop.
- Put the session in a dedicate DPDK thread.
+ Receives (dequeues) ``nb_ops`` virtio-crypto requests from guest, parses
+ them to DPDK Crypto Operations, and fills the ``ops`` with parsing results.
-* Callback register
+* ``rte_vhost_crypto_finalize_requests(queue_id, ops, nb_ops)``
- Vhost supported vSwitch could call rte_vhost_driver_callback_register to
- register two callbacks, new_destory and destroy_device.
- When virtio device is activated or deactivated by guest virtual machine,
- the callback will be called, then vSwitch could put the device onto data
- core or remove the device from data core by setting or unsetting
- VIRTIO_DEV_RUNNING on the device flags.
+ After the ``ops`` are dequeued from Cryptodev, finalizes the jobs and
+ notifies the guest(s).
-* Read/write packets from/to guest virtual machine
+* ``rte_vhost_crypto_set_zero_copy(vid, option)``
- rte_vhost_enqueue_burst transmit host packets to guest.
- rte_vhost_dequeue_burst receives packets from guest.
+ Enable or disable zero copy feature of the vhost crypto backend.
-* Feature enable/disable
+* ``rte_vhost_async_channel_register(vid, queue_id, config, ops)``
- Now one negotiate-able feature in vhost is merge-able.
- vSwitch could enable/disable this feature for performance consideration.
+ Register an async copy device channel for a vhost queue after vring
+ is enabled. Following device ``config`` must be specified together
+ with the registration:
-Vhost Implementation
---------------------
+ * ``features``
-Vhost cuse implementation
-~~~~~~~~~~~~~~~~~~~~~~~~~
-When vSwitch registers the vhost driver, it will register a cuse device driver
-into the system and creates a character device file. This cuse driver will
-receive vhost open/release/IOCTL message from QEMU simulator.
+ This field is used to specify async copy device features.
-When the open call is received, vhost driver will create a vhost device for the
-virtio device in the guest.
+ ``RTE_VHOST_ASYNC_INORDER`` represents the async copy device can
+ guarantee the order of copy completion is the same as the order
+ of copy submission.
-When VHOST_SET_MEM_TABLE IOCTL is received, vhost searches the memory region
-to find the starting user space virtual address that maps the memory of guest
-virtual machine. Through this virtual address and the QEMU pid, vhost could
-find the file QEMU uses to map the guest memory. Vhost maps this file into its
-address space, in this way vhost could fully access the guest physical memory,
-which means vhost could access the shared virtio ring and the guest physical
-address specified in the entry of the ring.
+ Currently, only ``RTE_VHOST_ASYNC_INORDER`` capable device is
+ supported by vhost.
-The guest virtual machine tells the vhost whether the virtio device is ready
-for processing or is de-activated through VHOST_NET_SET_BACKEND message.
-The registered callback from vSwitch will be called.
+ Applications must provide following ``ops`` callbacks for vhost lib to
+ work with the async copy devices:
-When the release call is released, vhost will destroy the device.
+ * ``transfer_data(vid, queue_id, descs, opaque_data, count)``
-Vhost user implementation
-~~~~~~~~~~~~~~~~~~~~~~~~~
-When vSwitch registers a vhost driver, it will create a unix domain socket server
-into the system. This server will listen for a connection and process the vhost message from
-QEMU simulator.
+ vhost invokes this function to submit copy data to the async devices.
+ For non-async_inorder capable devices, ``opaque_data`` could be used
+ for identifying the completed packets.
-When there is a new socket connection, it means a new virtio device has been created in
-the guest virtual machine, and the vhost driver will create a vhost device for this virtio device.
+ * ``check_completed_copies(vid, queue_id, opaque_data, max_packets)``
-For messages with a file descriptor, the file descriptor could be directly used in the vhost
-process as it is already installed by unix domain socket.
+ vhost invokes this function to get the copy data completed by async
+ devices.
- * VHOST_SET_MEM_TABLE
- * VHOST_SET_VRING_KICK
- * VHOST_SET_VRING_CALL
- * VHOST_SET_LOG_FD
- * VHOST_SET_VRING_ERR
+* ``rte_vhost_async_channel_register_thread_unsafe(vid, queue_id, config, ops)``
-For VHOST_SET_MEM_TABLE message, QEMU will send us information for each memory region and its
-file descriptor in the ancillary data of the message. The fd is used to map that region.
+ Register an async copy device channel for a vhost queue without
+ performing any locking.
-There is no VHOST_NET_SET_BACKEND message as in vhost cuse to signal us whether virtio device
-is ready or should be stopped.
-VHOST_SET_VRING_KICK is used as the signal to put the vhost device onto data plane.
-VHOST_GET_VRING_BASE is used as the signal to remove vhost device from data plane.
+ This function is only safe to call in vhost callback functions
+ (i.e., struct vhost_device_ops).
+
+* ``rte_vhost_async_channel_unregister(vid, queue_id)``
+
+ Unregister the async copy device channel from a vhost queue.
+ Unregistration will fail, if the vhost queue has in-flight
+ packets that are not completed.
+
+ Unregister async copy devices in vring_state_changed() may
+ fail, as this API tries to acquire the spinlock of vhost
+ queue. The recommended way is to unregister async copy
+ devices for all vhost queues in destroy_device(), when a
+ virtio device is paused or shut down.
+
+* ``rte_vhost_async_channel_unregister_thread_unsafe(vid, queue_id)``
+
+ Unregister the async copy device channel for a vhost queue without
+ performing any locking.
+
+ This function is only safe to call in vhost callback functions
+ (i.e., struct vhost_device_ops).
+
+* ``rte_vhost_submit_enqueue_burst(vid, queue_id, pkts, count, comp_pkts, comp_count)``
+
+ Submit an enqueue request to transmit ``count`` packets from host to guest
+ by async data path. Successfully enqueued packets can be transfer completed
+ or being occupied by DMA engines; transfer completed packets are returned in
+ ``comp_pkts``, but others are not guaranteed to finish, when this API
+ call returns.
+
+ Applications must not free the packets submitted for enqueue until the
+ packets are completed.
+
+* ``rte_vhost_poll_enqueue_completed(vid, queue_id, pkts, count)``
+
+ Poll enqueue completion status from async data path. Completed packets
+ are returned to applications through ``pkts``.
+
+* ``rte_vhost_async_get_inflight(vid, queue_id)``
+
+ This function returns the amount of in-flight packets for the vhost
+ queue using async acceleration.
+
+* ``rte_vhost_clear_queue_thread_unsafe(vid, queue_id, **pkts, count)``
+
+ Clear inflight packets which are submitted to DMA engine in vhost async data
+ path. Completed packets are returned to applications through ``pkts``.
+
+Vhost-user Implementations
+--------------------------
+
+Vhost-user uses Unix domain sockets for passing messages. This means the DPDK
+vhost-user implementation has two options:
+
+* DPDK vhost-user acts as the server.
+
+ DPDK will create a Unix domain socket server file and listen for
+ connections from the frontend.
+
+ Note, this is the default mode, and the only mode before DPDK v16.07.
+
+
+* DPDK vhost-user acts as the client.
+
+ Unlike the server mode, this mode doesn't create the socket file;
+ it just tries to connect to the server (which responses to create the
+ file instead).
+
+ When the DPDK vhost-user application restarts, DPDK vhost-user will try to
+ connect to the server again. This is how the "reconnect" feature works.
+
+ .. Note::
+ * The "reconnect" feature requires **QEMU v2.7** (or above).
+
+ * The vhost supported features must be exactly the same before and
+ after the restart. For example, if TSO is disabled and then enabled,
+ nothing will work and issues undefined might happen.
+
+No matter which mode is used, once a connection is established, DPDK
+vhost-user will start receiving and processing vhost messages from QEMU.
+
+For messages with a file descriptor, the file descriptor can be used directly
+in the vhost process as it is already installed by the Unix domain socket.
+
+The supported vhost messages are:
+
+* ``VHOST_SET_MEM_TABLE``
+* ``VHOST_SET_VRING_KICK``
+* ``VHOST_SET_VRING_CALL``
+* ``VHOST_SET_LOG_FD``
+* ``VHOST_SET_VRING_ERR``
+
+For ``VHOST_SET_MEM_TABLE`` message, QEMU will send information for each
+memory region and its file descriptor in the ancillary data of the message.
+The file descriptor is used to map that region.
+
+``VHOST_SET_VRING_KICK`` is used as the signal to put the vhost device into
+the data plane, and ``VHOST_GET_VRING_BASE`` is used as the signal to remove
+the vhost device from the data plane.
When the socket connection is closed, vhost will destroy the device.
+Guest memory requirement
+------------------------
+
+* Memory pre-allocation
+
+ For non-async data path, guest memory pre-allocation is not a
+ must. This can help save of memory. If users really want the guest memory
+ to be pre-allocated (e.g., for performance reason), we can add option
+ ``-mem-prealloc`` when starting QEMU. Or, we can lock all memory at vhost
+ side which will force memory to be allocated when mmap at vhost side;
+ option --mlockall in ovs-dpdk is an example in hand.
+
+ For async data path, we force the VM memory to be pre-allocated at vhost
+ lib when mapping the guest memory; and also we need to lock the memory to
+ prevent pages being swapped out to disk.
+
+* Memory sharing
+
+ Make sure ``share=on`` QEMU option is given. vhost-user will not work with
+ a QEMU version without shared memory mapping.
+
Vhost supported vSwitch reference
---------------------------------
-For more vhost details and how to support vhost in vSwitch, please refer to vhost example in the
-DPDK Sample Applications Guide.
+For more vhost details and how to support vhost in vSwitch, please refer to
+the vhost example in the DPDK Sample Applications Guide.
+
+Vhost data path acceleration (vDPA)
+-----------------------------------
+
+vDPA supports selective datapath in vhost-user lib by enabling virtio ring
+compatible devices to serve virtio driver directly for datapath acceleration.
+
+``rte_vhost_driver_attach_vdpa_device`` is used to configure the vhost device
+with accelerated backend.
+
+Also vhost device capabilities are made configurable to adopt various devices.
+Such capabilities include supported features, protocol features, queue number.
+
+Finally, a set of device ops is defined for device specific operations:
+
+* ``get_queue_num``
+
+ Called to get supported queue number of the device.
+
+* ``get_features``
+
+ Called to get supported features of the device.
+
+* ``get_protocol_features``
+
+ Called to get supported protocol features of the device.
+
+* ``dev_conf``
+
+ Called to configure the actual device when the virtio device becomes ready.
+
+* ``dev_close``
+
+ Called to close the actual device when the virtio device is stopped.
+
+* ``set_vring_state``
+
+ Called to change the state of the vring in the actual device when vring state
+ changes.
+
+* ``set_features``
+
+ Called to set the negotiated features to device.
+
+* ``migration_done``
+
+ Called to allow the device to response to RARP sending.
+
+* ``get_vfio_group_fd``
+
+ Called to get the VFIO group fd of the device.
+
+* ``get_vfio_device_fd``
+
+ Called to get the VFIO device fd of the device.
+
+* ``get_notify_area``
+
+ Called to get the notify area info of the queue.
git.droids-corp.org / dpdk.git / blobdiff