[PATCH 4/4] libvhost-user: add write_msg cb to dev struct

[Albert Esteve <aesteve@redhat.com>]

Add vu_write_msg_cb type as a member of the VuDev
struct.

In order to interact with the virtio-dmabuf
API, vhost-user backends have available a special
message type that can be sent to the frontend
in Qemu, in order to add, lookup, or remove
entries.

To send these messages and avoid code replication,
backends will need the write_msg method to be exposed
to them, similarly to how the read_msg is for
receiving messages.

Signed-off-by: Albert Esteve <aesteve@redhat.com>
---
 subprojects/libvhost-user/libvhost-user.c |  1 +
 subprojects/libvhost-user/libvhost-user.h | 16 ++++++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/subprojects/libvhost-user/libvhost-user.c b/subprojects/libvhost-user/libvhost-user.c
index 6b4b721225..c50b353915 100644
--- a/subprojects/libvhost-user/libvhost-user.c
+++ b/subprojects/libvhost-user/libvhost-user.c
@@ -2115,6 +2115,7 @@ vu_init(VuDev *dev,
     dev->sock = socket;
     dev->panic = panic;
     dev->read_msg = read_msg ? read_msg : vu_message_read_default;
+    dev->write_msg = vu_message_write;
     dev->set_watch = set_watch;
     dev->remove_watch = remove_watch;
     dev->iface = iface;
diff --git a/subprojects/libvhost-user/libvhost-user.h b/subprojects/libvhost-user/libvhost-user.h
index 784db65f7c..f5d7162886 100644
--- a/subprojects/libvhost-user/libvhost-user.h
+++ b/subprojects/libvhost-user/libvhost-user.h
@@ -242,6 +242,7 @@ typedef void (*vu_set_features_cb) (VuDev *dev, uint64_t features);
 typedef int (*vu_process_msg_cb) (VuDev *dev, VhostUserMsg *vmsg,
                                   int *do_reply);
 typedef bool (*vu_read_msg_cb) (VuDev *dev, int sock, VhostUserMsg *vmsg);
+typedef bool (*vu_write_msg_cb) (VuDev *dev, int sock, VhostUserMsg *vmsg);
 typedef void (*vu_queue_set_started_cb) (VuDev *dev, int qidx, bool started);
 typedef bool (*vu_queue_is_processed_in_order_cb) (VuDev *dev, int qidx);
 typedef int (*vu_get_config_cb) (VuDev *dev, uint8_t *config, uint32_t len);
@@ -429,6 +430,21 @@ struct VuDev {
      */
     vu_read_msg_cb read_msg;
 
+    /*
+     * @write_msg: custom method to write vhost-user message
+     *
+     * Write data to vhost_user socket fd from the passed
+     * VhostUserMsg *vmsg struct.
+     *
+     * For the details, please refer to vu_message_write in libvhost-user.c
+     * which will be used by default when calling vu_unit.
+     * No custom method is allowed.
+     *
+     * Returns: true if vhost-user message successfully sent, false otherwise.
+     *
+     */
+    vu_write_msg_cb write_msg;
+
     /*
      * @set_watch: add or update the given fd to the watch set,
      * call cb when condition is met.
-- 
2.40.0