lists replica entries that can be garbage collected.
specifies the disk pool.
may be one of the following constant:
the first call must have this flag set to allocate buffers and
all the following calls must have this flag set.
final call to terminate the list and free resources.
This routine returns a pointer to a structure containing the current replica
entry if the operation was successful or NULL if all entries have been returned
or if the operation failed. In the latter case,
is set appropriately.
Memory could not be allocated for the output buffer.