[PATCH 2/4] vhost-user: add shared_object msg

[Albert Esteve]

Add new vhost-user protocol message
`VHOST_USER_BACKEND_SHARED_OBJECT`. This new
message is sent from vhost-user back-ends
to interact with the virtio-dmabuf table
in order to add, remove, or lookup for
virtio dma-buf shared objects.

The action taken in the front-end depends
on the type stored in the payload struct.

In the libvhost-user library add a helper
function (`vu_get_shared_object`) to send a
message to lookup for the dma-buf given the
UUID. Other operations, i.e., add and remove
entries in the shared objects table, will have
to be handled directly in the back-end.

Signed-off-by: Albert Esteve <aesteve@redhat.com>
---
 docs/interop/vhost-user.rst               | 15 +++++
 hw/virtio/vhost-user.c                    | 68 +++++++++++++++++++++++
 subprojects/libvhost-user/libvhost-user.c | 39 +++++++++++++
 subprojects/libvhost-user/libvhost-user.h | 30 ++++++++++
 4 files changed, 152 insertions(+)

diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst
index 5a070adbc1..d3d8db41e5 100644
--- a/docs/interop/vhost-user.rst
+++ b/docs/interop/vhost-user.rst
@@ -1528,6 +1528,21 @@ is sent by the front-end.
 
   The state.num field is currently reserved and must be set to 0.
 
+``VHOST_USER_BACKEND_SHARED_OBJECT``
+  :id: 6
+  :equivalent ioctl: N/A
+  :request payload: ``struct VhostUserShared``
+  :reply payload: ``struct VhostUserShared`` (only for ``LOOKUP`` requests)
+
+  Backends that need to interact with the virtio-dmabuf shared table API
+  can send this message. The operation is determined by the ``type`` member
+  of the payload struct. The valid values for the operation type are
+  ``VHOST_SHARED_OBJECT_*`` members, i.e., ``ADD``, ``LOOKUP``, and ``REMOVE``.
+  ``LOOKUP`` operations require the ``VHOST_USER_NEED_REPLY_MASK`` flag to be
+  set by the back-end, and the front-end will then send the dma-buf fd as
+  a response if the UUID matches an object in the table, or a negative value
+  otherwise.
+
 .. _reply_ack:
 
 VHOST_USER_PROTOCOL_F_REPLY_ACK
diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index e5285df4ba..d0b889282a 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -10,6 +10,7 @@
 
 #include "qemu/osdep.h"
 #include "qapi/error.h"
+#include "hw/virtio/virtio-dmabuf.h"
 #include "hw/virtio/vhost.h"
 #include "hw/virtio/vhost-user.h"
 #include "hw/virtio/vhost-backend.h"
@@ -20,6 +21,7 @@
 #include "sysemu/kvm.h"
 #include "qemu/error-report.h"
 #include "qemu/main-loop.h"
+#include "qemu/uuid.h"
 #include "qemu/sockets.h"
 #include "sysemu/runstate.h"
 #include "sysemu/cryptodev.h"
@@ -138,6 +140,7 @@ typedef enum VhostUserSlaveRequest {
     VHOST_USER_BACKEND_IOTLB_MSG = 1,
     VHOST_USER_BACKEND_CONFIG_CHANGE_MSG = 2,
     VHOST_USER_BACKEND_VRING_HOST_NOTIFIER_MSG = 3,
+    VHOST_USER_BACKEND_SHARED_OBJECT = 6,
     VHOST_USER_BACKEND_MAX
 }  VhostUserSlaveRequest;
 
@@ -200,6 +203,18 @@ typedef struct VhostUserInflight {
     uint16_t queue_size;
 } VhostUserInflight;
 
+typedef enum VhostUserSharedType {
+    VHOST_SHARED_OBJECT_ADD = 0,
+    VHOST_SHARED_OBJECT_LOOKUP,
+    VHOST_SHARED_OBJECT_REMOVE,
+} VhostUserSharedType;
+
+typedef struct VhostUserShared {
+    unsigned char uuid[16];
+    VhostUserSharedType type;
+    int dmabuf_fd;
+} VhostUserShared;
+
 typedef struct {
     VhostUserRequest request;
 
@@ -224,6 +239,7 @@ typedef union {
         VhostUserCryptoSession session;
         VhostUserVringArea area;
         VhostUserInflight inflight;
+        VhostUserShared object;
 } VhostUserPayload;
 
 typedef struct VhostUserMsg {
@@ -1591,6 +1607,52 @@ static int 
vhost_user_slave_handle_vring_host_notifier(struct vhost_dev *dev,
     return 0;
 }
 
+static int vhost_user_backend_handle_shared_object(VhostUserShared *object)
+{
+    QemuUUID uuid;
+    memcpy(uuid.data, object->uuid, sizeof(object->uuid));
+
+    switch (object->type) {
+    case VHOST_SHARED_OBJECT_ADD:
+        return virtio_add_dmabuf(uuid, object->dmabuf_fd);
+    case VHOST_SHARED_OBJECT_LOOKUP:
+        object->dmabuf_fd = virtio_lookup_dmabuf(uuid);
+        if (object->dmabuf_fd < 0) {
+            return object->dmabuf_fd;
+        }
+        break;
+    case VHOST_SHARED_OBJECT_REMOVE:
+        return virtio_remove_resource(uuid);
+    }
+
+    return 0;
+}
+
+static bool
+vhost_user_backend_send_dmabuf_fd(QIOChannel *ioc, VhostUserHeader *hdr,
+                                  VhostUserPayload *payload)
+{
+    Error *local_err = NULL;
+    struct iovec iov[2];
+    if (hdr->flags & VHOST_USER_NEED_REPLY_MASK) {
+        hdr->flags &= ~VHOST_USER_NEED_REPLY_MASK;
+        hdr->flags |= VHOST_USER_REPLY_MASK;
+
+        hdr->size = sizeof(payload->object);
+
+        iov[0].iov_base = hdr;
+        iov[0].iov_len = VHOST_USER_HDR_SIZE;
+        iov[1].iov_base = payload;
+        iov[1].iov_len = hdr->size;
+
+        if (qio_channel_writev_all(ioc, iov, ARRAY_SIZE(iov), &local_err)) {
+            error_report_err(local_err);
+            return false;
+        }
+    }
+    return true;
+}
+
 static void close_slave_channel(struct vhost_user *u)
 {
     g_source_destroy(u->slave_src);
@@ -1648,6 +1710,12 @@ static gboolean slave_read(QIOChannel *ioc, GIOCondition 
condition,
         ret = vhost_user_slave_handle_vring_host_notifier(dev, &payload.area,
                                                           fd ? fd[0] : -1);
         break;
+    case VHOST_USER_BACKEND_SHARED_OBJECT:
+        ret = vhost_user_backend_handle_shared_object(&payload.object);
+        if (!vhost_user_backend_send_dmabuf_fd(ioc, &hdr, &payload)) {
+            goto err;
+        }
+        break;
     default:
         error_report("Received unexpected msg type: %d.", hdr.request);
         ret = -EINVAL;
diff --git a/subprojects/libvhost-user/libvhost-user.c 
b/subprojects/libvhost-user/libvhost-user.c
index 8fb61e2df2..6b4b721225 100644
--- a/subprojects/libvhost-user/libvhost-user.c
+++ b/subprojects/libvhost-user/libvhost-user.c
@@ -1403,6 +1403,45 @@ bool vu_set_queue_host_notifier(VuDev *dev, VuVirtq *vq, 
int fd,
     return vu_process_message_reply(dev, &vmsg);
 }
 
+bool
+vu_get_shared_object(VuDev *dev, unsigned char uuid[UUID_LEN], int *dmabuf_fd)
+{
+    int result = false;
+    VhostUserMsg msg_reply;
+    VhostUserMsg msg = {
+        .request = VHOST_USER_BACKEND_SHARED_OBJECT,
+        .size = sizeof(msg.payload.object),
+        .flags = VHOST_USER_VERSION | VHOST_USER_NEED_REPLY_MASK,
+        .payload.object = {
+            .type = VHOST_SHARED_OBJECT_LOOKUP,
+        },
+    };
+
+    memcpy(msg.payload.object.uuid, uuid, sizeof(uuid[0]) * UUID_LEN);
+
+    pthread_mutex_lock(&dev->slave_mutex);
+    if (!vu_message_write(dev, dev->slave_fd, &msg)) {
+        goto out;
+    }
+
+    if (!vu_message_read_default(dev, dev->slave_fd, &msg_reply)) {
+        goto out;
+    }
+
+    if (msg_reply.request != msg.request) {
+        DPRINT("Received unexpected msg type. Expected %d, received %d",
+               msg.request, msg_reply.request);
+        goto out;
+    }
+
+    *dmabuf_fd = msg_reply.payload.object.dmabuf_fd;
+    result = *dmabuf_fd > 0;
+out:
+    pthread_mutex_unlock(&dev->slave_mutex);
+
+    return result;
+}
+
 static bool
 vu_set_vring_call_exec(VuDev *dev, VhostUserMsg *vmsg)
 {
diff --git a/subprojects/libvhost-user/libvhost-user.h 
b/subprojects/libvhost-user/libvhost-user.h
index 49208cceaa..784db65f7c 100644
--- a/subprojects/libvhost-user/libvhost-user.h
+++ b/subprojects/libvhost-user/libvhost-user.h
@@ -119,6 +119,7 @@ typedef enum VhostUserSlaveRequest {
     VHOST_USER_BACKEND_VRING_HOST_NOTIFIER_MSG = 3,
     VHOST_USER_BACKEND_VRING_CALL = 4,
     VHOST_USER_BACKEND_VRING_ERR = 5,
+    VHOST_USER_BACKEND_SHARED_OBJECT = 6,
     VHOST_USER_BACKEND_MAX
 }  VhostUserSlaveRequest;
 
@@ -172,6 +173,20 @@ typedef struct VhostUserInflight {
     uint16_t queue_size;
 } VhostUserInflight;
 
+typedef enum VhostUserSharedType {
+    VHOST_SHARED_OBJECT_ADD = 0,
+    VHOST_SHARED_OBJECT_LOOKUP,
+    VHOST_SHARED_OBJECT_REMOVE,
+} VhostUserSharedType;
+
+#define UUID_LEN 16
+
+typedef struct VhostUserShared {
+    unsigned char uuid[UUID_LEN];
+    VhostUserSharedType type;
+    int dmabuf_fd;
+} VhostUserShared;
+
 #if defined(_WIN32) && (defined(__x86_64__) || defined(__i386__))
 # define VU_PACKED __attribute__((gcc_struct, packed))
 #else
@@ -199,6 +214,7 @@ typedef struct VhostUserMsg {
         VhostUserConfig config;
         VhostUserVringArea area;
         VhostUserInflight inflight;
+        VhostUserShared object;
     } payload;
 
     int fds[VHOST_MEMORY_BASELINE_NREGIONS];
@@ -539,6 +555,20 @@ void vu_set_queue_handler(VuDev *dev, VuVirtq *vq,
 bool vu_set_queue_host_notifier(VuDev *dev, VuVirtq *vq, int fd,
                                 int size, int offset);
 
+/**
+ * vu_get_shared_object:
+ * @dev: a VuDev context
+ * @uuid: UUID of the shared object
+ * @dmabuf_fd: output dma-buf file descriptor
+ *
+ * Lookup for a virtio shared object (i.e., dma-buf fd) associated with the
+ * received UUID. Result, if found, is stored in the dmabuf_fd argument.
+ *
+ * Returns: whether the virtio object was found.
+ */
+bool vu_get_shared_object(VuDev *dev, unsigned char uuid[UUID_LEN],
+                          int *dmabuf_fd);
+
 /**
  * vu_queue_set_notification:
  * @dev: a VuDev context
-- 
2.40.0