mirror of
https://github.com/xemu-project/xemu.git
synced 2024-12-14 15:28:40 +00:00
60915dc469
This patch basically reverts commit d1f8b30e.
It turned out that it breaks stuff, so revert it:
http://lists.nongnu.org/archive/html/qemu-devel/2015-10/msg00949.html
CC: "Michael S. Tsirkin" <mst@redhat.com>
Reported-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
405 lines
13 KiB
Plaintext
405 lines
13 KiB
Plaintext
Vhost-user Protocol
|
|
===================
|
|
|
|
Copyright (c) 2014 Virtual Open Systems Sarl.
|
|
|
|
This work is licensed under the terms of the GNU GPL, version 2 or later.
|
|
See the COPYING file in the top-level directory.
|
|
===================
|
|
|
|
This protocol is aiming to complement the ioctl interface used to control the
|
|
vhost implementation in the Linux kernel. It implements the control plane needed
|
|
to establish virtqueue sharing with a user space process on the same host. It
|
|
uses communication over a Unix domain socket to share file descriptors in the
|
|
ancillary data of the message.
|
|
|
|
The protocol defines 2 sides of the communication, master and slave. Master is
|
|
the application that shares its virtqueues, in our case QEMU. Slave is the
|
|
consumer of the virtqueues.
|
|
|
|
In the current implementation QEMU is the Master, and the Slave is intended to
|
|
be a software Ethernet switch running in user space, such as Snabbswitch.
|
|
|
|
Master and slave can be either a client (i.e. connecting) or server (listening)
|
|
in the socket communication.
|
|
|
|
Message Specification
|
|
---------------------
|
|
|
|
Note that all numbers are in the machine native byte order. A vhost-user message
|
|
consists of 3 header fields and a payload:
|
|
|
|
------------------------------------
|
|
| request | flags | size | payload |
|
|
------------------------------------
|
|
|
|
* Request: 32-bit type of the request
|
|
* Flags: 32-bit bit field:
|
|
- Lower 2 bits are the version (currently 0x01)
|
|
- Bit 2 is the reply flag - needs to be sent on each reply from the slave
|
|
* Size - 32-bit size of the payload
|
|
|
|
|
|
Depending on the request type, payload can be:
|
|
|
|
* A single 64-bit integer
|
|
-------
|
|
| u64 |
|
|
-------
|
|
|
|
u64: a 64-bit unsigned integer
|
|
|
|
* A vring state description
|
|
---------------
|
|
| index | num |
|
|
---------------
|
|
|
|
Index: a 32-bit index
|
|
Num: a 32-bit number
|
|
|
|
* A vring address description
|
|
--------------------------------------------------------------
|
|
| index | flags | size | descriptor | used | available | log |
|
|
--------------------------------------------------------------
|
|
|
|
Index: a 32-bit vring index
|
|
Flags: a 32-bit vring flags
|
|
Descriptor: a 64-bit user address of the vring descriptor table
|
|
Used: a 64-bit user address of the vring used ring
|
|
Available: a 64-bit user address of the vring available ring
|
|
Log: a 64-bit guest address for logging
|
|
|
|
* Memory regions description
|
|
---------------------------------------------------
|
|
| num regions | padding | region0 | ... | region7 |
|
|
---------------------------------------------------
|
|
|
|
Num regions: a 32-bit number of regions
|
|
Padding: 32-bit
|
|
|
|
A region is:
|
|
-----------------------------------------------------
|
|
| guest address | size | user address | mmap offset |
|
|
-----------------------------------------------------
|
|
|
|
Guest address: a 64-bit guest address of the region
|
|
Size: a 64-bit size
|
|
User address: a 64-bit user address
|
|
mmap offset: 64-bit offset where region starts in the mapped memory
|
|
|
|
In QEMU the vhost-user message is implemented with the following struct:
|
|
|
|
typedef struct VhostUserMsg {
|
|
VhostUserRequest request;
|
|
uint32_t flags;
|
|
uint32_t size;
|
|
union {
|
|
uint64_t u64;
|
|
struct vhost_vring_state state;
|
|
struct vhost_vring_addr addr;
|
|
VhostUserMemory memory;
|
|
VhostUserLog log;
|
|
};
|
|
} QEMU_PACKED VhostUserMsg;
|
|
|
|
Communication
|
|
-------------
|
|
|
|
The protocol for vhost-user is based on the existing implementation of vhost
|
|
for the Linux Kernel. Most messages that can be sent via the Unix domain socket
|
|
implementing vhost-user have an equivalent ioctl to the kernel implementation.
|
|
|
|
The communication consists of master sending message requests and slave sending
|
|
message replies. Most of the requests don't require replies. Here is a list of
|
|
the ones that do:
|
|
|
|
* VHOST_GET_FEATURES
|
|
* VHOST_GET_PROTOCOL_FEATURES
|
|
* VHOST_GET_VRING_BASE
|
|
* VHOST_SET_LOG_BASE (if VHOST_USER_PROTOCOL_F_LOG_SHMFD)
|
|
|
|
There are several messages that the master sends with file descriptors passed
|
|
in the ancillary data:
|
|
|
|
* VHOST_SET_MEM_TABLE
|
|
* VHOST_SET_LOG_BASE (if VHOST_USER_PROTOCOL_F_LOG_SHMFD)
|
|
* VHOST_SET_LOG_FD
|
|
* VHOST_SET_VRING_KICK
|
|
* VHOST_SET_VRING_CALL
|
|
* VHOST_SET_VRING_ERR
|
|
|
|
If Master is unable to send the full message or receives a wrong reply it will
|
|
close the connection. An optional reconnection mechanism can be implemented.
|
|
|
|
Any protocol extensions are gated by protocol feature bits,
|
|
which allows full backwards compatibility on both master
|
|
and slave.
|
|
As older slaves don't support negotiating protocol features,
|
|
a feature bit was dedicated for this purpose:
|
|
#define VHOST_USER_F_PROTOCOL_FEATURES 30
|
|
|
|
Multiple queue support
|
|
----------------------
|
|
|
|
Multiple queue is treated as a protocol extension, hence the slave has to
|
|
implement protocol features first. The multiple queues feature is supported
|
|
only when the protocol feature VHOST_USER_PROTOCOL_F_MQ (bit 0) is set.
|
|
|
|
The max number of queues the slave supports can be queried with message
|
|
VHOST_USER_GET_PROTOCOL_FEATURES. Master should stop when the number of
|
|
requested queues is bigger than that.
|
|
|
|
As all queues share one connection, the master uses a unique index for each
|
|
queue in the sent message to identify a specified queue. One queue pair
|
|
is enabled initially. More queues are enabled dynamically, by sending
|
|
message VHOST_USER_SET_VRING_ENABLE.
|
|
|
|
Migration
|
|
---------
|
|
|
|
During live migration, the master may need to track the modifications
|
|
the slave makes to the memory mapped regions. The client should mark
|
|
the dirty pages in a log. Once it complies to this logging, it may
|
|
declare the VHOST_F_LOG_ALL vhost feature.
|
|
|
|
All the modifications to memory pointed by vring "descriptor" should
|
|
be marked. Modifications to "used" vring should be marked if
|
|
VHOST_VRING_F_LOG is part of ring's features.
|
|
|
|
Dirty pages are of size:
|
|
#define VHOST_LOG_PAGE 0x1000
|
|
|
|
The log memory fd is provided in the ancillary data of
|
|
VHOST_USER_SET_LOG_BASE message when the slave has
|
|
VHOST_USER_PROTOCOL_F_LOG_SHMFD protocol feature.
|
|
|
|
The size of the log may be computed by using all the known guest
|
|
addresses. The log covers from address 0 to the maximum of guest
|
|
regions. In pseudo-code, to mark page at "addr" as dirty:
|
|
|
|
page = addr / VHOST_LOG_PAGE
|
|
log[page / 8] |= 1 << page % 8
|
|
|
|
Use atomic operations, as the log may be concurrently manipulated.
|
|
|
|
VHOST_USER_SET_LOG_FD is an optional message with an eventfd in
|
|
ancillary data, it may be used to inform the master that the log has
|
|
been modified.
|
|
|
|
Once the source has finished migration, VHOST_USER_RESET_OWNER message
|
|
will be sent by the source. No further update must be done before the
|
|
destination takes over with new regions & rings.
|
|
|
|
Protocol features
|
|
-----------------
|
|
|
|
#define VHOST_USER_PROTOCOL_F_MQ 0
|
|
#define VHOST_USER_PROTOCOL_F_LOG_SHMFD 1
|
|
#define VHOST_USER_PROTOCOL_F_RARP 2
|
|
|
|
Message types
|
|
-------------
|
|
|
|
* VHOST_USER_GET_FEATURES
|
|
|
|
Id: 1
|
|
Equivalent ioctl: VHOST_GET_FEATURES
|
|
Master payload: N/A
|
|
Slave payload: u64
|
|
|
|
Get from the underlying vhost implementation the features bitmask.
|
|
Feature bit VHOST_USER_F_PROTOCOL_FEATURES signals slave support for
|
|
VHOST_USER_GET_PROTOCOL_FEATURES and VHOST_USER_SET_PROTOCOL_FEATURES.
|
|
|
|
* VHOST_USER_SET_FEATURES
|
|
|
|
Id: 2
|
|
Ioctl: VHOST_SET_FEATURES
|
|
Master payload: u64
|
|
|
|
Enable features in the underlying vhost implementation using a bitmask.
|
|
Feature bit VHOST_USER_F_PROTOCOL_FEATURES signals slave support for
|
|
VHOST_USER_GET_PROTOCOL_FEATURES and VHOST_USER_SET_PROTOCOL_FEATURES.
|
|
|
|
* VHOST_USER_GET_PROTOCOL_FEATURES
|
|
|
|
Id: 15
|
|
Equivalent ioctl: VHOST_GET_FEATURES
|
|
Master payload: N/A
|
|
Slave payload: u64
|
|
|
|
Get the protocol feature bitmask from the underlying vhost implementation.
|
|
Only legal if feature bit VHOST_USER_F_PROTOCOL_FEATURES is present in
|
|
VHOST_USER_GET_FEATURES.
|
|
Note: slave that reported VHOST_USER_F_PROTOCOL_FEATURES must support
|
|
this message even before VHOST_USER_SET_FEATURES was called.
|
|
|
|
* VHOST_USER_SET_PROTOCOL_FEATURES
|
|
|
|
Id: 16
|
|
Ioctl: VHOST_SET_FEATURES
|
|
Master payload: u64
|
|
|
|
Enable protocol features in the underlying vhost implementation.
|
|
Only legal if feature bit VHOST_USER_F_PROTOCOL_FEATURES is present in
|
|
VHOST_USER_GET_FEATURES.
|
|
Note: slave that reported VHOST_USER_F_PROTOCOL_FEATURES must support
|
|
this message even before VHOST_USER_SET_FEATURES was called.
|
|
|
|
* VHOST_USER_SET_OWNER
|
|
|
|
Id: 3
|
|
Equivalent ioctl: VHOST_SET_OWNER
|
|
Master payload: N/A
|
|
|
|
Issued when a new connection is established. It sets the current Master
|
|
as an owner of the session. This can be used on the Slave as a
|
|
"session start" flag.
|
|
|
|
* VHOST_USER_RESET_OWNER
|
|
|
|
Id: 4
|
|
Equivalent ioctl: VHOST_RESET_OWNER
|
|
Master payload: N/A
|
|
|
|
Issued when a new connection is about to be closed. The Master will no
|
|
longer own this connection (and will usually close it).
|
|
|
|
* VHOST_USER_SET_MEM_TABLE
|
|
|
|
Id: 5
|
|
Equivalent ioctl: VHOST_SET_MEM_TABLE
|
|
Master payload: memory regions description
|
|
|
|
Sets the memory map regions on the slave so it can translate the vring
|
|
addresses. In the ancillary data there is an array of file descriptors
|
|
for each memory mapped region. The size and ordering of the fds matches
|
|
the number and ordering of memory regions.
|
|
|
|
* VHOST_USER_SET_LOG_BASE
|
|
|
|
Id: 6
|
|
Equivalent ioctl: VHOST_SET_LOG_BASE
|
|
Master payload: u64
|
|
Slave payload: N/A
|
|
|
|
Sets logging shared memory space.
|
|
When slave has VHOST_USER_PROTOCOL_F_LOG_SHMFD protocol
|
|
feature, the log memory fd is provided in the ancillary data of
|
|
VHOST_USER_SET_LOG_BASE message, the size and offset of shared
|
|
memory area provided in the message.
|
|
|
|
|
|
* VHOST_USER_SET_LOG_FD
|
|
|
|
Id: 7
|
|
Equivalent ioctl: VHOST_SET_LOG_FD
|
|
Master payload: N/A
|
|
|
|
Sets the logging file descriptor, which is passed as ancillary data.
|
|
|
|
* VHOST_USER_SET_VRING_NUM
|
|
|
|
Id: 8
|
|
Equivalent ioctl: VHOST_SET_VRING_NUM
|
|
Master payload: vring state description
|
|
|
|
Sets the number of vrings for this owner.
|
|
|
|
* VHOST_USER_SET_VRING_ADDR
|
|
|
|
Id: 9
|
|
Equivalent ioctl: VHOST_SET_VRING_ADDR
|
|
Master payload: vring address description
|
|
Slave payload: N/A
|
|
|
|
Sets the addresses of the different aspects of the vring.
|
|
|
|
* VHOST_USER_SET_VRING_BASE
|
|
|
|
Id: 10
|
|
Equivalent ioctl: VHOST_SET_VRING_BASE
|
|
Master payload: vring state description
|
|
|
|
Sets the base offset in the available vring.
|
|
|
|
* VHOST_USER_GET_VRING_BASE
|
|
|
|
Id: 11
|
|
Equivalent ioctl: VHOST_USER_GET_VRING_BASE
|
|
Master payload: vring state description
|
|
Slave payload: vring state description
|
|
|
|
Get the available vring base offset.
|
|
|
|
* VHOST_USER_SET_VRING_KICK
|
|
|
|
Id: 12
|
|
Equivalent ioctl: VHOST_SET_VRING_KICK
|
|
Master payload: u64
|
|
|
|
Set the event file descriptor for adding buffers to the vring. It
|
|
is passed in the ancillary data.
|
|
Bits (0-7) of the payload contain the vring index. Bit 8 is the
|
|
invalid FD flag. This flag is set when there is no file descriptor
|
|
in the ancillary data. This signals that polling should be used
|
|
instead of waiting for a kick.
|
|
|
|
* VHOST_USER_SET_VRING_CALL
|
|
|
|
Id: 13
|
|
Equivalent ioctl: VHOST_SET_VRING_CALL
|
|
Master payload: u64
|
|
|
|
Set the event file descriptor to signal when buffers are used. It
|
|
is passed in the ancillary data.
|
|
Bits (0-7) of the payload contain the vring index. Bit 8 is the
|
|
invalid FD flag. This flag is set when there is no file descriptor
|
|
in the ancillary data. This signals that polling will be used
|
|
instead of waiting for the call.
|
|
|
|
* VHOST_USER_SET_VRING_ERR
|
|
|
|
Id: 14
|
|
Equivalent ioctl: VHOST_SET_VRING_ERR
|
|
Master payload: u64
|
|
|
|
Set the event file descriptor to signal when error occurs. It
|
|
is passed in the ancillary data.
|
|
Bits (0-7) of the payload contain the vring index. Bit 8 is the
|
|
invalid FD flag. This flag is set when there is no file descriptor
|
|
in the ancillary data.
|
|
|
|
* VHOST_USER_GET_QUEUE_NUM
|
|
|
|
Id: 17
|
|
Equivalent ioctl: N/A
|
|
Master payload: N/A
|
|
Slave payload: u64
|
|
|
|
Query how many queues the backend supports. This request should be
|
|
sent only when VHOST_USER_PROTOCOL_F_MQ is set in quried protocol
|
|
features by VHOST_USER_GET_PROTOCOL_FEATURES.
|
|
|
|
* VHOST_USER_SET_VRING_ENABLE
|
|
|
|
Id: 18
|
|
Equivalent ioctl: N/A
|
|
Master payload: vring state description
|
|
|
|
Signal slave to enable or disable corresponding vring.
|
|
|
|
* VHOST_USER_SEND_RARP
|
|
|
|
Id: 19
|
|
Equivalent ioctl: N/A
|
|
Master payload: u64
|
|
|
|
Ask vhost user backend to broadcast a fake RARP to notify the migration
|
|
is terminated for guest that does not support GUEST_ANNOUNCE.
|
|
Only legal if feature bit VHOST_USER_F_PROTOCOL_FEATURES is present in
|
|
VHOST_USER_GET_FEATURES and protocol feature bit VHOST_USER_PROTOCOL_F_RARP
|
|
is present in VHOST_USER_GET_PROTOCOL_FEATURES.
|
|
The first 6 bytes of the payload contain the mac address of the guest to
|
|
allow the vhost user backend to construct and broadcast the fake RARP.
|