Add flag to indicate external users to block device

Certain operations such as drive_del or resize cannot be performed
while external users (eg. block migration) reference the block device.

Add a flag to indicate that.
Signed-off-by: NMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block.c

@@ -2774,6 +2774,17 @@ int64_t bdrv_get_dirty_count(BlockDriverState *bs)
     return bs->dirty_count;
 }
 
+void bdrv_set_in_use(BlockDriverState *bs, int in_use)
+{
+    assert(bs->in_use != in_use);
+    bs->in_use = in_use;
+}
+
+int bdrv_in_use(BlockDriverState *bs)
+{
+    return bs->in_use;
+}
+
 int bdrv_img_create(const char *filename, const char *fmt,
                     const char *base_filename, const char *base_fmt,
                     char *options, uint64_t img_size, int flags)

block.h

@@ -241,6 +241,8 @@ void bdrv_reset_dirty(BlockDriverState *bs, int64_t cur_sector,
                       int nr_sectors);
 int64_t bdrv_get_dirty_count(BlockDriverState *bs);
 
+void bdrv_set_in_use(BlockDriverState *bs, int in_use);
+int bdrv_in_use(BlockDriverState *bs);
 
 typedef enum {
     BLKDBG_L1_UPDATE,

block_int.h

@@ -199,6 +199,7 @@ struct BlockDriverState {
     char device_name[32];
     unsigned long *dirty_bitmap;
     int64_t dirty_count;
+    int in_use; /* users other than guest access, eg. block migration */
     QTAILQ_ENTRY(BlockDriverState) list;
     void *private;
 };