vhost-user-blk: Add support to reconnect backend

Since we now support the message VHOST_USER_GET_INFLIGHT_FD
and VHOST_USER_SET_INFLIGHT_FD. The backend is able to restart
safely because it can track inflight I/O in shared memory.
This patch allows qemu to reconnect the backend after
connection closed.

Signed-off-by: Xie Yongji <xieyongji@baidu.com>
Signed-off-by: Ni Xun <nixun@baidu.com>
Signed-off-by: Zhang Yu <zhangyu31@baidu.com>
Message-Id: <20190320112646.3712-7-xieyongji@baidu.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/block/vhost-user-blk.c

@@ -192,17 +192,27 @@ static void vhost_user_blk_set_status(VirtIODevice *vdev, uint8_t status)
 {
     VHostUserBlk *s = VHOST_USER_BLK(vdev);
     bool should_start = vdev->started;
+    int ret;
 
     if (!vdev->vm_running) {
         should_start = false;
     }
 
+    if (!s->connected) {
+        return;
+    }
+
     if (s->dev.started == should_start) {
         return;
     }
 
     if (should_start) {
-        vhost_user_blk_start(vdev);
+        ret = vhost_user_blk_start(vdev);
+        if (ret < 0) {
+            error_report("vhost-user-blk: vhost start failed: %s",
+                         strerror(-ret));
+            qemu_chr_fe_disconnect(&s->chardev);
+        }
     } else {
         vhost_user_blk_stop(vdev);
     }
@@ -238,12 +248,16 @@ static uint64_t vhost_user_blk_get_features(VirtIODevice *vdev,
 static void vhost_user_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq)
 {
     VHostUserBlk *s = VHOST_USER_BLK(vdev);
-    int i;
+    int i, ret;
 
     if (!vdev->start_on_kick) {
         return;
     }
 
+    if (!s->connected) {
+        return;
+    }
+
     if (s->dev.started) {
         return;
     }
@@ -251,7 +265,13 @@ static void vhost_user_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq)
     /* Some guests kick before setting VIRTIO_CONFIG_S_DRIVER_OK so start
      * vhost here instead of waiting for .set_status().
      */
-    vhost_user_blk_start(vdev);
+    ret = vhost_user_blk_start(vdev);
+    if (ret < 0) {
+        error_report("vhost-user-blk: vhost start failed: %s",
+                     strerror(-ret));
+        qemu_chr_fe_disconnect(&s->chardev);
+        return;
+    }
 
     /* Kick right away to begin processing requests already in vring */
     for (i = 0; i < s->dev.nvqs; i++) {
@@ -271,11 +291,103 @@ static void vhost_user_blk_reset(VirtIODevice *vdev)
     vhost_dev_free_inflight(s->inflight);
 }
 
+static int vhost_user_blk_connect(DeviceState *dev)
+{
+    VirtIODevice *vdev = VIRTIO_DEVICE(dev);
+    VHostUserBlk *s = VHOST_USER_BLK(vdev);
+    int ret = 0;
+
+    if (s->connected) {
+        return 0;
+    }
+    s->connected = true;
+
+    s->dev.nvqs = s->num_queues;
+    s->dev.vqs = s->vqs;
+    s->dev.vq_index = 0;
+    s->dev.backend_features = 0;
+
+    vhost_dev_set_config_notifier(&s->dev, &blk_ops);
+
+    ret = vhost_dev_init(&s->dev, &s->vhost_user, VHOST_BACKEND_TYPE_USER, 0);
+    if (ret < 0) {
+        error_report("vhost-user-blk: vhost initialization failed: %s",
+                     strerror(-ret));
+        return ret;
+    }
+
+    /* restore vhost state */
+    if (vdev->started) {
+        ret = vhost_user_blk_start(vdev);
+        if (ret < 0) {
+            error_report("vhost-user-blk: vhost start failed: %s",
+                         strerror(-ret));
+            return ret;
+        }
+    }
+
+    return 0;
+}
+
+static void vhost_user_blk_disconnect(DeviceState *dev)
+{
+    VirtIODevice *vdev = VIRTIO_DEVICE(dev);
+    VHostUserBlk *s = VHOST_USER_BLK(vdev);
+
+    if (!s->connected) {
+        return;
+    }
+    s->connected = false;
+
+    if (s->dev.started) {
+        vhost_user_blk_stop(vdev);
+    }
+
+    vhost_dev_cleanup(&s->dev);
+}
+
+static gboolean vhost_user_blk_watch(GIOChannel *chan, GIOCondition cond,
+                                     void *opaque)
+{
+    DeviceState *dev = opaque;
+    VirtIODevice *vdev = VIRTIO_DEVICE(dev);
+    VHostUserBlk *s = VHOST_USER_BLK(vdev);
+
+    qemu_chr_fe_disconnect(&s->chardev);
+
+    return true;
+}
+
+static void vhost_user_blk_event(void *opaque, int event)
+{
+    DeviceState *dev = opaque;
+    VirtIODevice *vdev = VIRTIO_DEVICE(dev);
+    VHostUserBlk *s = VHOST_USER_BLK(vdev);
+
+    switch (event) {
+    case CHR_EVENT_OPENED:
+        if (vhost_user_blk_connect(dev) < 0) {
+            qemu_chr_fe_disconnect(&s->chardev);
+            return;
+        }
+        s->watch = qemu_chr_fe_add_watch(&s->chardev, G_IO_HUP,
+                                         vhost_user_blk_watch, dev);
+        break;
+    case CHR_EVENT_CLOSED:
+        vhost_user_blk_disconnect(dev);
+        if (s->watch) {
+            g_source_remove(s->watch);
+            s->watch = 0;
+        }
+        break;
+    }
+}
+
 static void vhost_user_blk_device_realize(DeviceState *dev, Error **errp)
 {
     VirtIODevice *vdev = VIRTIO_DEVICE(dev);
     VHostUserBlk *s = VHOST_USER_BLK(vdev);
-    struct vhost_virtqueue *vqs = NULL;
+    Error *err = NULL;
     int i, ret;
 
     if (!s->chardev.chr) {
@@ -306,27 +418,29 @@ static void vhost_user_blk_device_realize(DeviceState *dev, Error **errp)
     }
 
     s->inflight = g_new0(struct vhost_inflight, 1);
+    s->vqs = g_new(struct vhost_virtqueue, s->num_queues);
+    s->watch = 0;
+    s->connected = false;
 
-    s->dev.nvqs = s->num_queues;
+    qemu_chr_fe_set_handlers(&s->chardev,  NULL, NULL, vhost_user_blk_event,
-    s->dev.vqs = g_new(struct vhost_virtqueue, s->dev.nvqs);
+                             NULL, (void *)dev, NULL, true);
-    s->dev.vq_index = 0;
-    s->dev.backend_features = 0;
-    vqs = s->dev.vqs;
 
-    vhost_dev_set_config_notifier(&s->dev, &blk_ops);
+reconnect:
-
+    if (qemu_chr_fe_wait_connected(&s->chardev, &err) < 0) {
-    ret = vhost_dev_init(&s->dev, &s->vhost_user, VHOST_BACKEND_TYPE_USER, 0);
+        error_report_err(err);
-    if (ret < 0) {
-        error_setg(errp, "vhost-user-blk: vhost initialization failed: %s",
-                   strerror(-ret));
         goto virtio_err;
     }
 
+    /* check whether vhost_user_blk_connect() failed or not */
+    if (!s->connected) {
+        goto reconnect;
+    }
+
     ret = vhost_dev_get_config(&s->dev, (uint8_t *)&s->blkcfg,
                                sizeof(struct virtio_blk_config));
     if (ret < 0) {
-        error_setg(errp, "vhost-user-blk: get block config failed");
+        error_report("vhost-user-blk: get block config failed");
-        goto vhost_err;
+        goto reconnect;
     }
 
     if (s->blkcfg.num_queues != s->num_queues) {
@@ -335,10 +449,8 @@ static void vhost_user_blk_device_realize(DeviceState *dev, Error **errp)
 
     return;
 
-vhost_err:
-    vhost_dev_cleanup(&s->dev);
 virtio_err:
-    g_free(vqs);
+    g_free(s->vqs);
     g_free(s->inflight);
     virtio_cleanup(vdev);
     vhost_user_cleanup(&s->vhost_user);
@@ -348,12 +460,13 @@ static void vhost_user_blk_device_unrealize(DeviceState *dev, Error **errp)
 {
     VirtIODevice *vdev = VIRTIO_DEVICE(dev);
     VHostUserBlk *s = VHOST_USER_BLK(dev);
-    struct vhost_virtqueue *vqs = s->dev.vqs;
 
     virtio_set_status(vdev, 0);
+    qemu_chr_fe_set_handlers(&s->chardev,  NULL, NULL, NULL,
+                             NULL, NULL, NULL, false);
     vhost_dev_cleanup(&s->dev);
     vhost_dev_free_inflight(s->inflight);
-    g_free(vqs);
+    g_free(s->vqs);
     g_free(s->inflight);
     virtio_cleanup(vdev);
     vhost_user_cleanup(&s->vhost_user);

include/hw/virtio/vhost-user-blk.h

@@ -38,6 +38,9 @@ typedef struct VHostUserBlk {
     struct vhost_dev dev;
     struct vhost_inflight *inflight;
     VhostUserState vhost_user;
+    struct vhost_virtqueue *vqs;
+    guint watch;
+    bool connected;
 } VHostUserBlk;
 
 #endif