block-backend: add blk_get_max_iov()

Add a function to query BlockLimits.max_iov.
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

block/block-backend.c

@@ -1023,6 +1023,11 @@ int blk_get_max_transfer_length(BlockBackend *blk)
     }
 }
 
+int blk_get_max_iov(BlockBackend *blk)
+{
+    return blk->bs->bl.max_iov;
+}
+
 void blk_set_guest_block_size(BlockBackend *blk, int align)
 {
     blk->guest_block_size = align;

include/sysemu/block-backend.h

@@ -146,6 +146,7 @@ void blk_lock_medium(BlockBackend *blk, bool locked);
 void blk_eject(BlockBackend *blk, bool eject_flag);
 int blk_get_flags(BlockBackend *blk);
 int blk_get_max_transfer_length(BlockBackend *blk);
+int blk_get_max_iov(BlockBackend *blk);
 void blk_set_guest_block_size(BlockBackend *blk, int align);
 void *blk_blockalign(BlockBackend *blk, size_t size);
 bool blk_op_is_blocked(BlockBackend *blk, BlockOpType op, Error **errp);