The present invention provides a system, method, and computer program product that enables application instances to pass block mode storage requests directly to a physical I/O adapter without run-time involvement from the local operating system or hypervisor. In one aspect of the present invention, a mechanism is provided for handling user space query and modification operations for querying and modifying attributes of allocations of linear block addresses of a physical storage device. For modification, it is determined if there are sufficient available resources for the modification of the allocation. In addition, it is determined if there are any I/O transactions active on the allocation before performing the modification. Modification of the attributes of the allocation may be performed only if there are sufficient available resources and only if there are no active I/O transactions on the allocation being modified.