diff options
Diffstat (limited to 'docs/specs/vhost-user.txt')
| -rw-r--r-- | docs/specs/vhost-user.txt | 64 |
1 files changed, 55 insertions, 9 deletions
diff --git a/docs/specs/vhost-user.txt b/docs/specs/vhost-user.txt index 26dde2ec42..df40cec54e 100644 --- a/docs/specs/vhost-user.txt +++ b/docs/specs/vhost-user.txt @@ -87,6 +87,14 @@ Depending on the request type, payload can be: User address: a 64-bit user address mmap offset: 64-bit offset where region starts in the mapped memory +* Log description + --------------------------- + | log size | log offset | + --------------------------- + log size: size of area used for logging + log offset: offset from start of supplied file descriptor + where logging starts (i.e. where guest address 0 would be logged) + In QEMU the vhost-user message is implemented with the following struct: typedef struct VhostUserMsg { @@ -138,6 +146,23 @@ As older slaves don't support negotiating protocol features, a feature bit was dedicated for this purpose: #define VHOST_USER_F_PROTOCOL_FEATURES 30 +Starting and stopping rings +---------------------- +Each ring is initialized in a stopped state, client must not process it until +ring is enabled. + +If VHOST_USER_F_PROTOCOL_FEATURES has been negotiated, client must start and +stop ring processing upon receiving VHOST_USER_SET_VRING_ENABLE with parameters +1 and 0 respoectively. + +If VHOST_USER_F_PROTOCOL_FEATURES has not been negotiated, client must start +ring processing upon receiving a kick (that is, detecting that file descriptor +is readable) on the descriptor specified by VHOST_USER_SET_VRING_KICK, and stop +ring processing upon receiving VHOST_USER_GET_VRING_BASE. + +While rings are running, client must support changing some configuration +aspects on the fly. + Multiple queue support ---------------------- @@ -162,9 +187,13 @@ 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. +To start/stop logging of data/used ring writes, server may send messages +VHOST_USER_SET_FEATURES with VHOST_F_LOG_ALL and VHOST_USER_SET_VRING_ADDR with +VHOST_VRING_F_LOG in ring's flags set to 1/0, respectively. + 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. +VHOST_VRING_F_LOG is part of ring's flags. Dirty pages are of size: #define VHOST_LOG_PAGE 0x1000 @@ -173,22 +202,35 @@ 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 +The size of the log is supplied as part of VhostUserMsg +which should be large enough to cover all known guest +addresses. Log starts at the supplied offset in the +supplied file descriptor. +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 +Where addr is the guest physical address. + Use atomic operations, as the log may be concurrently manipulated. +Note that when logging modifications to the used ring (when VHOST_VRING_F_LOG +is set for this ring), log_guest_addr should be used to calculate the log +offset: the write to first byte of the used ring is logged at this offset from +log start. Also note that this value might be outside the legal guest physical +address range (i.e. does not have to be covered by the VhostUserMemory table), +but the bit offset of the last byte of the ring must fall within +the size supplied by VhostUserLog. + 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. +Once the source has finished migration, rings will be stopped by +the source. No further update must be done before rings are +restarted. Protocol features ----------------- @@ -259,11 +301,13 @@ Message types * 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). + This is no longer used. Used to be sent to request stopping + all rings, but some clients interpreted it to also discard + connection state (this interpretation would lead to bugs). + It is recommended that clients either ignore this message, + or use it to stop all rings. * VHOST_USER_SET_MEM_TABLE @@ -388,6 +432,8 @@ Message types Master payload: vring state description Signal slave to enable or disable corresponding vring. + This request should be sent only when VHOST_USER_F_PROTOCOL_FEATURES + has been negotiated. * VHOST_USER_SEND_RARP |