[1/2] block: implement shared block device count

diff --git a/block.c b/block.c
index 9a1a0d1e73..cf8b94252c 100644
--- a/block.c
+++ b/block.c
@@ -3801,6 +3801,42 @@  BlockDriverState *bdrv_find_node(const char *node_name)
     return NULL;
 }
 
+void bdrv_find_shared(BlockDriverState *bs)
+{
+    BlockDriverState *tmp_bs;
+    int max_shared_no = 0;
+    unsigned long shared_bits = 0;
+
+    if (!bs->filename)
+        return;
+    QTAILQ_FOREACH(tmp_bs, &graph_bdrv_states, node_list) {
+        if (tmp_bs == bs)
+            continue;
+        if (!strcmp(bs->filename, tmp_bs->filename)) {
+            if (tmp_bs->shared_no > 0) {
+                set_bit(tmp_bs->shared_no - 1, &shared_bits);
+            }
+            max_shared_no++;
+        }
+    }
+    if (max_shared_no > 0) {
+        int bit;
+
+        QTAILQ_FOREACH(tmp_bs, &graph_bdrv_states, node_list) {
+            if (!strcmp(bs->filename, tmp_bs->filename) && !tmp_bs->shared_no) {
+                bit = find_first_zero_bit(&shared_bits, sizeof(unsigned long));
+                tmp_bs->shared_no = bit + 1;
+                set_bit(bit, &shared_bits);
+            }
+        }
+    }
+}
+
+int bdrv_get_shared(BlockDriverState *bs)
+{
+    return bs->shared_no;
+}
+
 /* Put this QMP function here so it can access the static graph_bdrv_states. */
 BlockDeviceInfoList *bdrv_named_nodes_list(Error **errp)
 {
diff --git a/hw/scsi/scsi-disk.c b/hw/scsi/scsi-disk.c
index 12431177a7..32c1d656b1 100644
--- a/hw/scsi/scsi-disk.c
+++ b/hw/scsi/scsi-disk.c
@@ -2333,6 +2333,7 @@  static void scsi_realize(SCSIDevice *dev, Error **errp)
 {
     SCSIDiskState *s = DO_UPCAST(SCSIDiskState, qdev, dev);
     Error *err = NULL;
+    int port_no;
 
     if (!s->qdev.conf.blk) {
         error_setg(errp, "drive property not set");
@@ -2396,6 +2397,11 @@  static void scsi_realize(SCSIDevice *dev, Error **errp)
     blk_set_guest_block_size(s->qdev.conf.blk, s->qdev.blocksize);
 
     blk_iostatus_enable(s->qdev.conf.blk);
+    bdrv_find_shared(blk_bs(s->qdev.conf.blk));
+    port_no = bdrv_get_shared(blk_bs(s->qdev.conf.blk));
+    if (port_no && !s->port_index) {
+        s->port_index = port_no;
+    }
 }
 
 static void scsi_hd_realize(SCSIDevice *dev, Error **errp)
diff --git a/include/block/block.h b/include/block/block.h
index c05cac57e5..5c03c1acfa 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -443,6 +443,8 @@  void bdrv_lock_medium(BlockDriverState *bs, bool locked);
 void bdrv_eject(BlockDriverState *bs, bool eject_flag);
 const char *bdrv_get_format_name(BlockDriverState *bs);
 BlockDriverState *bdrv_find_node(const char *node_name);
+void bdrv_find_shared(BlockDriverState *bs);
+int bdrv_get_shared(BlockDriverState *bs);
 BlockDeviceInfoList *bdrv_named_nodes_list(Error **errp);
 BlockDriverState *bdrv_lookup_bs(const char *device,
                                  const char *node_name,
diff --git a/include/block/block_int.h b/include/block/block_int.h
index a5482775ec..79c9c3a3aa 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -634,6 +634,8 @@  struct BlockDriverState {
     /* Flags honored during pwrite_zeroes (so far: BDRV_REQ_FUA,
      * BDRV_REQ_MAY_UNMAP) */
     unsigned int supported_zero_flags;
+    /* Shared instance count */
+    unsigned int shared_no;
 
     /* the following member gives a name to every node on the bs graph. */
     char node_name[32];