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vhost-user: document migration log

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Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Thibaut Collet <thibaut.collet@6wind.com>
This commit is contained in:
Marc-André Lureau 2015-10-09 17:17:29 +02:00 committed by Michael S. Tsirkin
parent 21e704256d
commit c62b91e580
1 changed files with 46 additions and 2 deletions
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48
docs/specs/vhost-user.txt
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@ -115,11 +115,13 @@ 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
@ -140,8 +142,7 @@ 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:
#define VHOST_USER_PROTOCOL_F_MQ 0
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
@ -152,6 +153,48 @@ 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
Message types
-------------
@ -236,6 +279,7 @@ Message types
Id: 6
Equivalent ioctl: VHOST_SET_LOG_BASE
Master payload: u64
Slave payload: N/A
Sets the logging base address.