关于linux获取硬盘序列号的一段代码？不太懂，求大神指教一下

#include
#include
#include
#include
#include
#include
#include
#include
#include
#include

static bool get_disk_name(std::string & disk_name)
{
disk_name.c_str();

std::ifstream ifs("/etc/mtab", std::ios::binary);
if (!ifs.is_open())
{
    return(false);
}

char line[4096] = { 0 };
while (!ifs.eof())
{
    ifs.getline(line, sizeof(line));
    if (!ifs.good())
    {
        break;
    }

    const char * disk = line;
    while (isspace(disk[0]))
    {
        ++disk;
    }

    const char * space = strchr(disk, ' ');
    if (NULL == space)
    {
        continue;
    }

    const char * mount = space + 1;
    while (isspace(mount[0]))
    {
        ++mount;
    }
    if ('/' != mount[0] || ' ' != mount[1])
    {
        continue;
    }

    while (space > disk && isdigit(space[-1]))
    {
        --space;
    }

    if (space > disk)
    {
        std::string(disk, space).swap(disk_name);
        break;
    }
}

ifs.close();

return(!disk_name.empty());

}

static void trim_serial(const void * serial, size_t serial_len, std::string & serial_no)
{
const char * serial_s = static_cast(serial);
const char * serial_e = serial_s + serial_len;
while (serial_s < serial_e)
{
if (isspace(serial_s[0]))
{
++serial_s;
}
else if ('\0' == serial_e[-1] || isspace(serial_e[-1]))
{
--serial_e;
}
else
{
break;
}
}

if (serial_s < serial_e)
{
    std::string(serial_s, serial_e).swap(serial_no);
}

}

static bool get_disk_serial_by_way_1(const std::string & disk_name, std::string & serial_no)
{
serial_no.clear();

int fd = open(disk_name.c_str(), O_RDONLY);
if (-1 == fd)
{
    return(false);
}

struct hd_driveid drive = { 0 };
if (0 == ioctl(fd, HDIO_GET_IDENTITY, &drive))
{
    trim_serial(drive.serial_no, sizeof(drive.serial_no), serial_no);
}

close(fd);

return(!serial_no.empty());

}

static bool scsi_io(
int fd, unsigned char * cdb,
unsigned char cdb_size, int xfer_dir,
unsigned char * data, unsigned int data_size,
unsigned char * sense, unsigned int sense_len
)
{
sg_io_hdr_t io_hdr = { 0 };
io_hdr.interface_id = 'S';

/* CDB */
io_hdr.cmdp = cdb;
io_hdr.cmd_len = cdb_size;

/* Where to store the sense_data, if there was an error */
io_hdr.sbp = sense;
io_hdr.mx_sb_len = sense_len;

/*
   Transfer direction, either in or out. Linux does not yet
   support bidirectional SCSI transfers ?
 */
io_hdr.dxfer_direction = xfer_dir;

/*
   Where to store the DATA IN/OUT from the device and how big the
   buffer is
 */
io_hdr.dxferp = data;
io_hdr.dxfer_len = data_size;

/* SCSI timeout in ms */
io_hdr.timeout = 5000;

if (ioctl(fd, SG_IO, &io_hdr) < 0)
{
    return(false);
}

/* now for the error processing */
if (SG_INFO_OK != (io_hdr.info & SG_INFO_OK_MASK) && io_hdr.sb_len_wr > 0)
{
    return(false);
}

if (io_hdr.masked_status || io_hdr.host_status || io_hdr.driver_status)
{
    return(false);
}

return(true);

}

static bool get_disk_serial_by_way_2(const std::string & disk_name, std::string & serial_no)
{
serial_no.clear();

int fd = open(disk_name.c_str(), O_RDONLY);
if (-1 == fd)
{
    return(false);
}

int version = 0;
if (ioctl(fd, SG_GET_VERSION_NUM, &version) < 0 || version < 30000)
{
    close(fd);
    return(false);
}

const unsigned int data_size = 0x00ff;
unsigned char data[data_size] = { 0 };
const unsigned int sense_len = 32;
unsigned char sense[sense_len] = { 0 };
unsigned char cdb[] = { 0x12, 0x01, 0x80, 0x00, 0x00, 0x00 };
cdb[3] = (data_size >> 8) & 0xff;
cdb[4] = (data_size & 0xff);

if (scsi_io(fd, cdb, sizeof(cdb), SG_DXFER_FROM_DEV, data, data_size, sense, sense_len))
{
    /* Page Length */
    int page_len = data[3];

    /* Unit Serial Number */
    trim_serial(data + 4, page_len, serial_no);
}

close(fd);

return(!serial_no.empty());

}

static bool parse_serial(const char * line, int line_size, const char * match_words, std::string & serial_no)
{
const char * serial_s = strstr(line, match_words);
if (NULL == serial_s)
{
return(false);
}
serial_s += strlen(match_words);
while (isspace(serial_s[0]))
{
++serial_s;
}

const char * serial_e = line + line_size;
const char * comma = strchr(serial_s, ',');
if (NULL != comma)
{
    serial_e = comma;
}

while (serial_e > serial_s && isspace(serial_e[-1]))
{
    --serial_e;
}

if (serial_e <= serial_s)
{
    return(false);
}

std::string(serial_s, serial_e).swap(serial_no);

return(true);

}

static void get_serial(const char * file_name, const char * match_words, std::string & serial_no)
{
serial_no.c_str();

std::ifstream ifs(file_name, std::ios::binary);
if (!ifs.is_open())
{
    return;
}

char line[4096] = { 0 };
while (!ifs.eof())
{
    ifs.getline(line, sizeof(line));
    if (!ifs.good())
    {
        break;
    }

    if (0 == ifs.gcount())
    {
        continue;
    }

    if (parse_serial(line, ifs.gcount() - 1, match_words, serial_no))
    {
        break;
    }
}

ifs.close();

}

static bool get_disk_serial_by_way_3(const std::string & disk_name, std::string & serial_no)
{
serial_no.c_str();

const char * hdparm_result = ".hdparm_result.txt";
char command[512] = { 0 };
snprintf(command, sizeof(command), "sudo hdparm -i %s | grep SerialNo > %s", disk_name.c_str(), hdparm_result);

if (0 == system(command))
{
    get_serial(hdparm_result, "SerialNo=", serial_no);
}

unlink(hdparm_result);

return(!serial_no.empty());

}

static bool get_disk_serial_by_way_4(std::string & serial_no)
{
serial_no.c_str();

const char * lshw_result = ".lshw_result.txt";
char command[512] = { 0 };
snprintf(command, sizeof(command), "sudo lshw -class disk | grep serial > %s", lshw_result);

if (0 == system(command))
{
    get_serial(lshw_result, "serial:", serial_no);
}

unlink(lshw_result);

return(!serial_no.empty());

}

static bool get_disk_serial_number(std::string & serial_no)
{
if (0 != getuid())
{
return(false);
}

std::string disk_name;
if (get_disk_name(disk_name))
{
    if (get_disk_serial_by_way_1(disk_name, serial_no))
    {
        return(true);
    }
    if (get_disk_serial_by_way_2(disk_name, serial_no))
    {
        return(true);
    }
    if (get_disk_serial_by_way_3(disk_name, serial_no))
    {
        return(true);
    }
}
if (get_disk_serial_by_way_4(serial_no))
{
    return(true);
}
return(false);

}

static void test_1()
{
std::string serial_no;
if (get_disk_serial_number(serial_no))
{
printf("serial_number: [%s]\n", serial_no.c_str());
}
else
{
printf("get serial number failed\n");
}
}

static void test_2()
{
std::string disk_name;
if (get_disk_name(disk_name))
{
printf("disk_name:[%s]\n", disk_name.c_str());
{
std::string serial_no;
get_disk_serial_by_way_1(disk_name, serial_no);
printf("get_serial_by_way_1:[%s]\n", serial_no.c_str());
}
{
std::string serial_no;
get_disk_serial_by_way_2(disk_name, serial_no);
printf("get_serial_by_way_2:[%s]\n", serial_no.c_str());
}
{
std::string serial_no;
get_disk_serial_by_way_3(disk_name, serial_no);
printf("get_serial_by_way_3:[%s]\n", serial_no.c_str());
}
}
{
std::string serial_no;
get_disk_serial_by_way_4(serial_no);
printf("get_serial_by_way_4:[%s]\n", serial_no.c_str());
}
}

int main(int argc, char * argv[])
{
printf("---------------\n");
test_1();
printf("---------------\n");
test_2();
printf("---------------\n");
return(0);
}

主要是想问一下那个最终存储了硬盘序列号的变量是哪个？我对linux下的C不是很熟，求帮忙~谢谢~

源代码就是没注释的，我也很为难，这个大概的原理应该是从linux下的文件里读取硬盘信息，但是他中间的一些操作我不是很懂，求帮忙啊~