struct blkif_request {
    operation => 0
    u => 1
}
struct blkif_request_rw {
    nr_segments => 0
    handle => 1
    id => 3
    sector_number => 11
    seg => 19
}
struct blkif_request_discard {
    flag => 0
    _pad1 => 1
    id => 3
    sector_number => 11
    nr_sectors => 19
    _pad3 => 27
}
struct blkif_request_other {
    _pad1 => 0
    _pad2 => 1
    id => 3
}
struct blkif_request_indirect {
    indirect_op => 0
    nr_segments => 1
    id => 3
    sector_number => 11
    handle => 19
    _pad2 => 21
    indirect_grefs => 23
    _pad3 => 55
}