struct blkif_request {
    operation => 0
    u => 1
}
struct blkif_request_rw {
    nr_segments => 0
    handle => 1
    _pad1 => 3
    id => 7
    sector_number => 15
    seg => 23
}
struct blkif_request_discard {
    flag => 0
    _pad1 => 1
    _pad2 => 3
    id => 7
    sector_number => 15
    nr_sectors => 23
    _pad3 => 31
}
struct blkif_request_other {
    _pad1 => 0
    _pad2 => 1
    _pad3 => 3
    id => 7
}
struct blkif_request_indirect {
    indirect_op => 0
    nr_segments => 1
    _pad1 => 3
    id => 7
    sector_number => 15
    handle => 23
    _pad2 => 25
    indirect_grefs => 27
    _pad3 => 59
}