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[Qemu-devel] [PULL 2/3] vhost-user: Introduce a new protocol feature REP
From: |
Michael S. Tsirkin |
Subject: |
[Qemu-devel] [PULL 2/3] vhost-user: Introduce a new protocol feature REPLY_ACK. |
Date: |
Wed, 10 Aug 2016 18:30:07 +0300 |
From: Prerna Saxena <address@hidden>
This introduces the VHOST_USER_PROTOCOL_F_REPLY_ACK.
If negotiated, client applications should send a u64 payload in
response to any message that contains the "need_reply" bit set
on the message flags. Setting the payload to "zero" indicates the
command finished successfully. Likewise, setting it to "non-zero"
indicates an error.
Currently implemented only for SET_MEM_TABLE.
Reviewed-by: Marc-André Lureau <address@hidden>
Signed-off-by: Prerna Saxena <address@hidden>
Reviewed-by: Michael S. Tsirkin <address@hidden>
Signed-off-by: Michael S. Tsirkin <address@hidden>
---
hw/virtio/vhost-user.c | 32 ++++++++++++++++++++++++++++++++
docs/specs/vhost-user.txt | 26 ++++++++++++++++++++++++++
2 files changed, 58 insertions(+)
diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index 1995fd2..b57454a 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -31,6 +31,7 @@ enum VhostUserProtocolFeature {
VHOST_USER_PROTOCOL_F_MQ = 0,
VHOST_USER_PROTOCOL_F_LOG_SHMFD = 1,
VHOST_USER_PROTOCOL_F_RARP = 2,
+ VHOST_USER_PROTOCOL_F_REPLY_ACK = 3,
VHOST_USER_PROTOCOL_F_MAX
};
@@ -84,6 +85,7 @@ typedef struct VhostUserMsg {
#define VHOST_USER_VERSION_MASK (0x3)
#define VHOST_USER_REPLY_MASK (0x1<<2)
+#define VHOST_USER_NEED_REPLY_MASK (0x1 << 3)
uint32_t flags;
uint32_t size; /* the following payload size */
union {
@@ -158,6 +160,25 @@ fail:
return -1;
}
+static int process_message_reply(struct vhost_dev *dev,
+ VhostUserRequest request)
+{
+ VhostUserMsg msg;
+
+ if (vhost_user_read(dev, &msg) < 0) {
+ return -1;
+ }
+
+ if (msg.request != request) {
+ error_report("Received unexpected msg type."
+ "Expected %d received %d",
+ request, msg.request);
+ return -1;
+ }
+
+ return msg.payload.u64 ? -1 : 0;
+}
+
static bool vhost_user_one_time_request(VhostUserRequest request)
{
switch (request) {
@@ -248,11 +269,18 @@ static int vhost_user_set_mem_table(struct vhost_dev *dev,
int fds[VHOST_MEMORY_MAX_NREGIONS];
int i, fd;
size_t fd_num = 0;
+ bool reply_supported = virtio_has_feature(dev->protocol_features,
+ VHOST_USER_PROTOCOL_F_REPLY_ACK);
+
VhostUserMsg msg = {
.request = VHOST_USER_SET_MEM_TABLE,
.flags = VHOST_USER_VERSION,
};
+ if (reply_supported) {
+ msg.flags |= VHOST_USER_NEED_REPLY_MASK;
+ }
+
for (i = 0; i < dev->mem->nregions; ++i) {
struct vhost_memory_region *reg = dev->mem->regions + i;
ram_addr_t offset;
@@ -288,6 +316,10 @@ static int vhost_user_set_mem_table(struct vhost_dev *dev,
return -1;
}
+ if (reply_supported) {
+ return process_message_reply(dev, msg.request);
+ }
+
return 0;
}
diff --git a/docs/specs/vhost-user.txt b/docs/specs/vhost-user.txt
index 777c49c..7890d71 100644
--- a/docs/specs/vhost-user.txt
+++ b/docs/specs/vhost-user.txt
@@ -37,6 +37,8 @@ consists of 3 header fields and a payload:
* 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
+ - Bit 3 is the need_reply flag - see VHOST_USER_PROTOCOL_F_REPLY_ACK for
+ details.
* Size - 32-bit size of the payload
@@ -126,6 +128,8 @@ the ones that do:
* VHOST_GET_VRING_BASE
* VHOST_SET_LOG_BASE (if VHOST_USER_PROTOCOL_F_LOG_SHMFD)
+[ Also see the section on REPLY_ACK protocol extension. ]
+
There are several messages that the master sends with file descriptors passed
in the ancillary data:
@@ -254,6 +258,7 @@ Protocol features
#define VHOST_USER_PROTOCOL_F_MQ 0
#define VHOST_USER_PROTOCOL_F_LOG_SHMFD 1
#define VHOST_USER_PROTOCOL_F_RARP 2
+#define VHOST_USER_PROTOCOL_F_REPLY_ACK 3
Message types
-------------
@@ -464,3 +469,24 @@ Message types
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.
+
+VHOST_USER_PROTOCOL_F_REPLY_ACK:
+-------------------------------
+The original vhost-user specification only demands replies for certain
+commands. This differs from the vhost protocol implementation where commands
+are sent over an ioctl() call and block until the client has completed.
+
+With this protocol extension negotiated, the sender (QEMU) can set the
+"need_reply" [Bit 3] flag to any command. This indicates that
+the client MUST respond with a Payload VhostUserMsg indicating success or
+failure. The payload should be set to zero on success or non-zero on failure,
+unless the message already has an explicit reply body.
+
+The response payload gives QEMU a deterministic indication of the result
+of the command. Today, QEMU is expected to terminate the main vhost-user
+loop upon receiving such errors. In future, qemu could be taught to be more
+resilient for selective requests.
+
+For the message types that already solicit a reply from the client, the
+presence of VHOST_USER_PROTOCOL_F_REPLY_ACK or need_reply bit being set brings
+no behavioural change. (See the 'Communication' section for details.)
--
MST
- [Qemu-devel] [PULL 0/3] virtio/vhost: fixes, Michael S. Tsirkin, 2016/08/10
- [Qemu-devel] [PULL 2/3] vhost-user: Introduce a new protocol feature REPLY_ACK.,
Michael S. Tsirkin <=
- [Qemu-devel] [PULL 1/3] vhost: check for vhost_ops before using., Michael S. Tsirkin, 2016/08/10
- [Qemu-devel] [PULL 3/3] vhost-user: Attempt to fix a race with set_mem_table., Michael S. Tsirkin, 2016/08/10
- Re: [Qemu-devel] [PULL 3/3] vhost-user: Attempt to fix a race with set_mem_table., Fam Zheng, 2016/08/12
- Re: [Qemu-devel] [PULL 3/3] vhost-user: Attempt to fix a race with set_mem_table., Prerna Saxena, 2016/08/12
- Re: [Qemu-devel] [PULL 3/3] vhost-user: Attempt to fix a race with set_mem_table., Marc-André Lureau, 2016/08/12
- Re: [Qemu-devel] [PULL 3/3] vhost-user: Attempt to fix a race with set_mem_table., Peter Maydell, 2016/08/12
- Re: [Qemu-devel] [PULL 3/3] vhost-user: Attempt to fix a race with set_mem_table., Michael S. Tsirkin, 2016/08/12
- Re: [Qemu-devel] [PULL 3/3] vhost-user: Attempt to fix a race with set_mem_table., Peter Maydell, 2016/08/15
- Re: [Qemu-devel] [PULL 3/3] vhost-user: Attempt to fix a race with set_mem_table., Michael S. Tsirkin, 2016/08/12
- Re: [Qemu-devel] [PULL 3/3] vhost-user: Attempt to fix a race with set_mem_table., Marc-André Lureau, 2016/08/12