Re: [Qemu-devel] [PATCH for-2.7 v5.1 1/2] vhost-user: Introduce a new protocol feature REPLY_ACK.

[Felipe Franciosi]

Heya,

On 29 Jul 2016, at 13:47, Marc-André Lureau 
<address@hidden<mailto:address@hidden>> wrote:

Hi

On Thu, Jul 28, 2016 at 11:07 AM, Prerna Saxena 
<address@hidden<mailto:address@hidden>> wrote:
From: Prerna Saxena <address@hidden<mailto: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.

Signed-off-by: Prerna Saxena <address@hidden<mailto:address@hidden>>
---
docs/specs/vhost-user.txt | 26 ++++++++++++++++++++++++++
hw/virtio/vhost-user.c    | 32 ++++++++++++++++++++++++++++++++
2 files changed, 58 insertions(+)

diff --git a/docs/specs/vhost-user.txt b/docs/specs/vhost-user.txt
index 777c49c..54b5c8f 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)

Unless/unless (for consistency, the rest of the document doesn't use
Upper-case inside parentheses)

Actually, if the sentence starts inside the parenthesis it should be capital.
See rule 2a:
http://www.grammarbook.com/punctuation/parens.asp

Prerna's text looks correct to me. If it's wrong in other places we should 
probably fix it there separately.


+
+This indicates to QEMU that the requested operation has deterministically
+been met or not. 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 behaviourial change. (See the 'Communication' section for details.)

See/see

Same as my comment above.

Cheers,
Felipe


diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index 495e09f..86e7ae0 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)

You could align it, and use the same style as the line above

    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)

bad indentation

+{
+    VhostUserMsg msg;
+
+    if (vhost_user_read(dev, &msg) < 0) {
+        return 0;

return -1

+    }
+
+    if (msg.request != request) {
+        error_report("Received unexpected msg type."
+                        "Expected %d received %d",
+                        request, msg.request);

bad indentation

+        return -1;
+    }
+
+    return msg.payload.u64 ? -1 : 0;
+}
+
static bool vhost_user_one_time_request(VhostUserRequest request)
{
    switch (request) {
@@ -239,11 +260,18 @@ 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);

bad indentation

+
    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;
@@ -277,6 +305,10 @@ static int vhost_user_set_mem_table(struct vhost_dev *dev,

    vhost_user_write(dev, &msg, fds, fd_num);

+    if (reply_supported) {
+        return process_message_reply(dev, msg.request);
+    }
+
    return 0;
}

--
1.8.1.2


Other than that, looks good to me, with those fixes


Reviewed-by: Marc-André Lureau <address@hidden<mailto:address@hidden>>



--
Marc-André Lureau