block-migration: efficiently encode zero blocks

this patch adds a efficient encoding for zero blocks by
adding a new flag indicating a block is completely zero.

additionally bdrv_write_zeros() is used at the destination
to efficiently write these zeroes. depending on the implementation
this avoids that the destination target gets fully provisioned.

Signed-off-by: Peter Lieven <pl@kamp.de>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/migration/migration.h b/include/migration/migration.h
index bc9fde0b2a..701709a1e9 100644
--- a/include/migration/migration.h
+++ b/include/migration/migration.h
@@ -124,6 +124,7 @@ void migrate_add_blocker(Error *reason);
 void migrate_del_blocker(Error *reason);
 
 bool migrate_rdma_pin_all(void);
+bool migrate_zero_blocks(void);
 
 bool migrate_auto_converge(void);