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1. 概述
在 GPT分区表 一文中,讲解了MBR分区表的一些概念。本文进一步给出了Windows系统上读取MBR的示例代码,以及MBR的具体数据,可进一步加深对MBR的理解。
在参考网上一些文章&代码的基础上,本文给出了下面的展示MBR的示例代码;同时最后针对几个典型问题,给出了一些解释和参考文档。
2. 代码
下面是代码:
/*** ref: http://noyesno.net/page/it/20100701-172* */
#include <stdio.h>
#include <windows.h>struct CHS {unsigned int header;unsigned int sector; unsigned int cylinder;
};struct partition_record {unsigned char boot_indicator;unsigned char os_type;struct CHS starting_chs;struct CHS ending_chs;unsigned int starting_LBA;unsigned int size_in_LBA;
};void dump_partition_record(const partition_record& record) {const double DISK_SECTOR_SIZE = 512.0;const size_t GB = 1024 * 1024 * 1024;printf("\tboot indicator: 0x%02x\n""\tOS Type: 0x%02x\n""\tStarting CHS: (%d, %d, %d)\n""\tEnding_CHS: (%d, %d, %d)\n""\tSize in LBA: %d\n""\tSize:%.2f\n\n",record.boot_indicator, record.os_type, record.starting_chs.cylinder,record.starting_chs.header,record.starting_chs.sector,record.ending_chs.cylinder,record.ending_chs.header,record.ending_chs.sector,record.size_in_LBA,record.size_in_LBA * DISK_SECTOR_SIZE / GB);
}// transform the 16-bytes buffer to partition record
void get_partition_record(unsigned char buffer[], partition_record& record) {record.boot_indicator = buffer[0];record.starting_chs.header = buffer[1];record.starting_chs.sector = buffer[2] & 0x3f;record.starting_chs.cylinder = (((buffer[2] & 0xff) >> 6) << 8) + buffer[3];record.os_type = buffer[4];record.ending_chs.header = buffer[5];record.ending_chs.sector = buffer[6] & 0x3f;record.ending_chs.cylinder = (((buffer[6] & 0xff) >> 6) << 8) + buffer[7];record.size_in_LBA = *(unsigned int*)(buffer + 12);
}void read_mbr(const char *devname){HANDLE hDevice = CreateFile(devname, GENERIC_READ, FILE_SHARE_WRITE, NULL, OPEN_EXISTING, 0, NULL); if (hDevice == INVALID_HANDLE_VALUE){ printf("Open %s failed, the error code is %d.\n", devname, GetLastError()); return; }DWORD dwRead = 0; const size_t DISK_SECTOR_SIZE = 512;unsigned char buffer[DISK_SECTOR_SIZE]; BOOL bSuccess = ReadFile(hDevice, buffer, DISK_SECTOR_SIZE, &dwRead, NULL); CloseHandle(hDevice);if ( !bSuccess || DISK_SECTOR_SIZE != dwRead) { printf("Error: read error! Read size = %d\n", dwRead); return; } size_t i, j;printf("%10s 0 1 2 3 4 5 6 7 8 9 A B C D E F \n", " "); for (i = 0; i < 32; i++) { printf("%.8XH: ", i); for (j = 0; j < 16; j++) {printf("%.2X ", buffer[i * 16 + j] & 0xFF); }printf("\n"); }printf("====MBR Partition Entries====\n");partition_record record = {0};for(i = 0x01be; i < 0x01FE; i += 16){get_partition_record(buffer + i, record);dump_partition_record(record);}
}int main(int argc, char *argv[]){const char* LOG_FILE = "./log.txt";freopen(LOG_FILE, "a", stdout); setbuf(stdout, NULL);read_mbr("\\\\.\\PhysicalDrive0");return 0;
}
运行结果如下:
0 1 2 3 4 5 6 7 8 9 A B C D E F
00000000H: 33 FF BE 00 02 8E D7 BC 00 7A BB A0 07 8B CE 8E
00000001H: DB 8E C3 F3 A4 EA 5D 00 A0 07 10 00 01 00 00 7A
00000002H: 00 00 00 00 00 00 00 00 00 00 07 66 8B 55 08 B4
00000003H: 42 C6 06 1F 00 7C 32 C0 66 89 16 22 00 BE 1A 00
00000004H: B2 80 CD 13 0F 82 CD 00 81 3E FE 03 55 AA C3 AC
00000005H: 0A C0 74 FA B4 0E BB 07 00 CD 10 EB F2 8B E9 8B
00000006H: D9 C6 06 2A 00 0C BF EE 01 B9 04 00 38 6D 04 74
00000007H: 37 E8 B7 FF 75 1F 66 B8 52 45 43 4F 66 39 06 03
00000008H: 02 74 0C 66 39 06 F0 03 75 0B C6 06 2A 00 07 8B
00000009H: DF C6 45 04 12 8A 45 04 3C 07 74 0A 3C 0B 74 06
0000000AH: 24 F5 3C 04 75 02 8B EF 88 2D 83 EF 10 E2 BD 0B
0000000BH: DB 74 3D 0B ED 74 39 8B FB F6 06 6D 01 04 75 76
0000000CH: F6 06 6D 01 02 75 73 B4 11 CD 16 75 5C 8A 16 6C
0000000DH: 01 0A D2 74 65 FE CA 78 17 36 8A 0E 6C 04 80 C1
0000000EH: 12 B4 11 CD 16 75 42 36 3A 0E 6C 04 75 F3 EB E5
0000000FH: 66 33 D2 E8 39 FF B1 04 BF BE 03 80 3D 80 74 5E
00000010H: 83 C7 10 E2 F6 B1 04 BF BE 03 80 7D 04 00 75 4E
00000011H: 83 C7 10 E2 F5 8B 36 70 01 E8 33 FF 8B 36 72 01
00000012H: E8 2C FF B4 00 CD 16 CD 18 B4 10 CD 16 3C 72 74
00000013H: 05 80 FC 85 75 BA 8B EF EB 07 F6 06 6D 01 10 74
00000014H: 06 A0 2A 00 88 45 04 8B FD C6 05 80 80 26 6D 01
00000015H: F9 66 33 D2 C6 06 1F 00 7A B4 43 E8 D8 FE E8 CA
00000016H: FE 8B 36 6E 01 75 B2 EA 00 7C 00 00 01 11 76 01
00000017H: 7B 01 82 01 87 01 45 72 72 32 00 0D 0A 45 72 72
00000018H: 31 00 45 72 72 33 00 0D 0A 50 72 65 73 73 20 46
00000019H: 31 31 20 66 6F 72 20 45 6D 65 72 67 65 6E 63 79
0000001AH: 20 52 65 63 6F 76 65 72 79 20 00 73 20 61 20 6B
0000001BH: 65 79 0D 0A 00 00 6C 01 32 F2 49 15 00 00 80 01
0000001CH: 01 00 07 EF FF FF 3F 00 00 00 D0 88 81 1D 00 EF
0000001DH: FF FF 07 EF FF FF 00 90 81 1D 00 60 07 1C 00 EF
0000001EH: FF FF 07 EF FF FF 10 F1 88 39 80 57 AF 00 00 00
0000001FH: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 55 AA
====MBR Partition Entries====boot indicator: 0x80OS Type: 0x07Starting CHS: (0, 1, 1)Ending_CHS: (1023, 239, 63)Size in LBA: 495028432Size:236.05boot indicator: 0x00OS Type: 0x07Starting CHS: (1023, 239, 63)Ending_CHS: (1023, 239, 63)Size in LBA: 470245376Size:224.23boot indicator: 0x00OS Type: 0x07Starting CHS: (1023, 239, 63)Ending_CHS: (1023, 239, 63)Size in LBA: 11491200Size:5.48boot indicator: 0x00OS Type: 0x00Starting CHS: (0, 0, 0)Ending_CHS: (0, 0, 0)Size in LBA: 0Size:0.00
下图是实际的硬盘中各分区的数据:
3. 典型问题
3.1 Vista上返回错误码5
vista上访问硬件时会有权限问题,比如上面代码CreateFile()在IDE中执行失败,返回错误码5. 规避的方法就是直接在资源管理器中运行exe程序,并选择“以管理员身份运行”。
3.2 超过8GB的CHS表示形式
在MBR的每个分区记录(partition record, partition entry)中,CHS(Cylinder Header Sector)部分是3个字节,如此最大表示8G的磁盘空间(粗略计算:8x3=24, 每个扇区512字节, 512 * 2^24 = 8GB)。但现在的磁盘空间最少都是几百G,因此CHS无法表示出正确的取值。为此,MBR通常规定0xfeffff表示非法的CHS,或无效的CHS;但UEFI规范规定的是0xffffff表示无效值,但如同上面代码运行结果显示的,在示例代码运行的系统上,却是0xefffff表示无效取值。
在这种情况下,都取Partition Entry中的起始LBA(StartingLBA)、以及LBA个数(SizeInLBA)两个字段来计算每个分区的起始位置、以及该分区的实际大小。
相关的两个链接提及了chs的特殊取值:
- gdisk - Interactive GUID partition table (GPT) manipulator
- MBR/EBR Partition Tables :系统地介绍了分区表的概念,以及CHS的计算方法
3.3 把打印重定向到文件
在上面的示例代码中,main()一开始把标准输出重定向到一个文件中。可以参考Android源码bootable/recovery/recovery.cpp的main()函数:
int
main(int argc, char **argv) {time_t start = time(NULL);// If these fail, there's not really anywhere to complain...freopen(TEMPORARY_LOG_FILE, "a", stdout); setbuf(stdout, NULL);freopen(TEMPORARY_LOG_FILE, "a", stderr); setbuf(stderr, NULL);
关于如何下载Android源码,请参考 The steps for download android source code。
3.4 磁盘管理相关的知识、以及MSDN相关的API
- 参考入口链接:http://msdn.microsoft.com/en-us/library/windows/desktop/aa363978%28v=vs.85%29.aspx
3.5 编码风格
Windows上面编码的风格和Linux及其他语言有相当大的差异,比如Windows的函数名是驼峰式、首字母大写;但Linux、以及STL等的命名均是小写字母、单词之间是下划线等风格。
为此,以上的示例代码主要侧重于Linux的编码习惯,如此会和Windows SDK API的风格存在差异。以此说明。
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