附录 B. sg_header，原始的sg控制结构

struct sg_header
{
    int pack_len;    /* [o] */
    int reply_len;   /* [i] */
    int pack_id;     /* [i->o] */
    int result;      /* [o] */
    unsigned int twelve_byte:1;     /* [i] */
    unsigned int target_status:5;   /* [o]+ */
    unsigned int host_status:8;     /* [o]+ */
    unsigned int driver_status:8;   /* [o]+ */
    unsigned int other_flags:10;    /* unused */
    unsigned char sense_buffer[SG_MAX_SENSE]; /* [o] */
};      /* This structure is 36 bytes long on i386 */