From 97f17497d162afdb82c8704bf097f0fee3724b2e Mon Sep 17 00:00:00 2001 From: "C.J. Collier" Date: Tue, 14 Jun 2016 07:50:17 -0700 Subject: Imported Upstream version 16.04 Change-Id: I77eadcd8538a9122e4773cbe55b24033dc451757 Signed-off-by: C.J. Collier --- doc/guides/prog_guide/vhost_lib.rst | 135 ++++++++++++++++++++++++++++++++++++ 1 file changed, 135 insertions(+) create mode 100644 doc/guides/prog_guide/vhost_lib.rst (limited to 'doc/guides/prog_guide/vhost_lib.rst') diff --git a/doc/guides/prog_guide/vhost_lib.rst b/doc/guides/prog_guide/vhost_lib.rst new file mode 100644 index 00000000..48e1fffb --- /dev/null +++ b/doc/guides/prog_guide/vhost_lib.rst @@ -0,0 +1,135 @@ +.. BSD LICENSE + Copyright(c) 2010-2014 Intel Corporation. All rights reserved. + All rights reserved. + + Redistribution and use in source and binary forms, with or without + modification, are permitted provided that the following conditions + are met: + + * Redistributions of source code must retain the above copyright + notice, this list of conditions and the following disclaimer. + * Redistributions in binary form must reproduce the above copyright + notice, this list of conditions and the following disclaimer in + the documentation and/or other materials provided with the + distribution. + * Neither the name of Intel Corporation nor the names of its + contributors may be used to endorse or promote products derived + from this software without specific prior written permission. + + THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS + "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT + LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR + A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT + OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, + SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT + LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, + DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY + THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT + (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE + OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. + +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. + +Vhost API Overview +------------------ + +* Vhost driver registration + + 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. + +* Vhost session start + + 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. + +* Callback register + + 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. + +* Read/write packets from/to guest virtual machine + + rte_vhost_enqueue_burst transmit host packets to guest. + rte_vhost_dequeue_burst receives packets from guest. + +* Feature enable/disable + + Now one negotiate-able feature in vhost is merge-able. + vSwitch could enable/disable this feature for performance consideration. + +Vhost Implementation +-------------------- + +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. + +When the open call is received, vhost driver will create a vhost device for the +virtio device in the guest. + +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. + +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. + +When the release call is released, vhost will destroy the device. + +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. + +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. + +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_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 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. + +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. + +When the socket connection is closed, vhost will destroy the device. + +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. -- cgit 1.2.3-korg