Signed-off-by: Marc-André Lureau <marcandre.lur...@redhat.com>
---
docs/specs/vhost-user.txt | 42 ++++++++++++++++++++++++++++++++++++++++++
1 file changed, 42 insertions(+)
diff --git a/docs/specs/vhost-user.txt b/docs/specs/vhost-user.txt
index 0062baa..2cf9ab4 100644
--- a/docs/specs/vhost-user.txt
+++ b/docs/specs/vhost-user.txt
@@ -120,6 +120,7 @@ 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
@@ -135,6 +136,11 @@ As older slaves don't support negotiating protocol
features,
a feature bit was dedicated for this purpose:
#define VHOST_USER_F_PROTOCOL_FEATURES 30
+Protocol features
+-----------------
+
+#define VHOST_USER_PROTOCOL_F_LOG_SHMFD 0
+
Message types
-------------
@@ -301,3 +307,39 @@ Message types
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.
+
+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 VHOST_F_LOG_ALL has a 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.
--
2.4.3
