migration: Create block capability

Create one capability for block migration and one parameter for
incremental block migration.

Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>

---

- address all Markus comments
- use Markus and Eric text descriptions
- change logic another time
- improve text messages

include/migration/block.h

@@ -20,4 +20,6 @@ uint64_t blk_mig_bytes_transferred(void);
 uint64_t blk_mig_bytes_remaining(void);
 uint64_t blk_mig_bytes_total(void);
 
+void migrate_set_block_enabled(bool value, Error **errp);
+
 #endif /* MIGRATION_BLOCK_H */

include/migration/migration.h

@@ -153,6 +153,9 @@ struct MigrationState
 
     /* The last error that occurred */
     Error *error;
+    /* Do we have to clean up -b/-i from old migrate parameters */
+    /* This feature is deprecated and will be removed */
+    bool must_remove_block_options;
 };
 
 void migrate_set_state(int *state, int old_state, int new_state);
@@ -265,6 +268,9 @@ bool migrate_colo_enabled(void);
 
 int64_t xbzrle_cache_resize(int64_t new_size);
 
+bool migrate_use_block(void);
+bool migrate_use_block_incremental(void);
+
 bool migrate_use_compression(void);
 int migrate_compress_level(void);
 int migrate_compress_threads(void);