什麼是MBR
硬盤的0柱面、0磁頭、1扇區稱爲主引導扇區，NANDFLASH由BLOCK和Sector組成，所以NANDFLASH的第0 BLOCK，第1 Sector爲主引導扇區，FDISK程序寫到該扇區的內容稱爲主引導記錄（MBR）。該記錄佔用512個字節，它用於硬盤啓動時將系統控制權交給用戶指定的，並在分區表中登記了的某個操作系統區。
MBR的組成
一個扇區的硬盤主引導記錄MBR由如圖6-15所示的4個部分組成。
·主引導程序（偏移地址0000H--0088H），它負責從活動分區中裝載，並運行系統引導程序。
·出錯信息數據區，偏移地址0089H--00E1H爲出錯信息，00E2H--01BDH全爲0字節。
·分區表（DPT,Disk Partition Table）含4個分區項，偏移地址01BEH--01FDH,每個分區表項長16個字節，共64字節爲分區項1、分區項2、分區項3、分區項4。
·結束標誌字，偏移地址01FE--01FF的2個字節值爲結束標誌55AA,如果該標誌錯誤系統就不能啓動。
|
0000-0088 |
Master Boot Record 主引導程序 |
主引導 程序 |
|
0089-01BD |
出錯信息數據區 |
數據區 |
|
01BE-01CD |
分區項1（16字節） |
分區表 |
|
01CE-01DD |
分區項2（16字節） |
|
|
01DE-01ED |
分區項3（16字節） |
|
|
01EE-01FD |
分區項4（16字節） |
|
|
01FE |
55 |
結束標誌 |
|
01FF |
AA |
圖6-15 MBR的組成結構圖
MBR中的分區信息結構
佔用512個字節的MBR中，偏移地址01BEH--01FDH的64個字節，爲4個分區項內容（分區信息表）。它是由磁盤介質類型及用戶在使用 FDISK定義分區說確定的。在實際應用中，FDISK對一個磁盤劃分的主分區可少於4個，但最多不超過4個。每個分區表的項目是16個字節，其內容含義 如表6-19所示。
表6-19 分區項表（16字節）內容及含義
|
存貯字節位 |
內容及含義 |
|
第1字節 |
引導標誌。若值爲80H表示活動分區，若值爲00H表示非活動分區。 |
|
第2、3、4字節 |
本分區的起始磁頭號、扇區號、柱面號。其中： 磁頭號——第2字節； 扇區號——第3字節的低6位； 柱面號——爲第3字節高2位+第4字節8位。 |
|
第5字節 |
分區類型符。 00H——表示該分區未用（即沒有指定）； 06H——FAT16基本分區； 0BH——FAT32基本分區； 05H——擴展分區； 07H——NTFS分區； 0FH——（LBA模式）擴展分區（83H爲Linux分區等）。 |
|
第6、7、8字節 |
本分區的結束磁頭號、扇區號、柱面號。其中： 磁頭號——第6字節； 扇區號——第7字節的低6位； 柱面號——第7字節的高2位+第8字節。 |
|
第9、10、11、12字節 |
本分區之前已用了的扇區數。 |
|
第13、14、15、16字節 |
本分區的總扇區數。 |
EBOOT中對NAND分區主要代碼，eboot目錄下的fmd.cpp文件，與NAND驅動基本相同，所以，要對NAND進行分區，就得對NAND驅動非常熟悉。透徹瞭解。然後就是
E:/WINCE500/PUBLIC/COMMON/OAK/DRIVERS/ETHDBG/BOOTPART/bootpart.cpp文件了。該文件主要通過調用NANDFLASH的讀寫操作來寫入MBR，也是今天主要的分析對象。
主要函數。
/* BP_OpenPartition
*
* Opens/creates a partition depending on the creation flags. If it is opening
* and the partition has already been opened, then it returns a handle to the
* opened partition. Otherwise, it loads the state information of that partition
* into memory and returns a handle.
*
* ENTRY
* dwStartSector - Logical sector to start the partition. NEXT_FREE_LOC if none
* specified. Ignored if opening existing partition.
* dwNumSectors - Number of logical sectors of the partition. USE_REMAINING_SPACE
* to indicate to take up the rest of the space on the flash for that partition (should
* only be used when creating extended partitions). This parameter is ignored
* if opening existing partition.
* dwPartType - Type of partition to create/open.
* fActive - TRUE indicates to create/open the active partition. FALSE for
* inactive.
* dwCreationFlags - PART_CREATE_NEW to create only. Fail if it already
* exists. PART_OPEN_EXISTING to open only. Fail if it doesn't exist.
* PART_OPEN_ALWAYS creates if it does not exist and opens if it
* does exist.
*
* EXIT
* Handle to the partition on success. INVALID_HANDLE_VALUE on error.
*/
HANDLE BP_OpenPartition(DWORD dwStartSector, DWORD dwNumSectors, DWORD dwPartType, BOOL fActive, DWORD dwCreationFlags)
注：示例代碼爲本人EBOOT中分區實現源碼（WINCE5.0+S3C2440+128MNAND,MBR寫在第4個BLOCK，分一個BINFS格式分區和一個FAT格式分區）。
BOOL WriteRegionsToBootMedia(DWORD dwImageStart, DWORD dwImageLength, DWORD dwLaunchAddr)
在把SDRAM中的NK燒寫到NAND中去之前，先創建一個BINFS分區。
hPart = BP_OpenPartition( (NK_START_BLOCK+1)*PAGES_PER_BLOCK, // next block of MBR BINFS_BLOCK*PAGES_PER_BLOCK,//SECTOR_TO_BLOCK_SIZE(FILE_TO_SECTOR_SIZE(dwBINFSPartLength))*PAGES_PER_BLOCK, //align to block
PART_BINFS,
TRUE,
PART_OPEN_ALWAYS);
第一個參數分區的起始sector 爲(NK_START_BLOCK+1)*PAGES_PER_BLOCK，
第二個參數分區的結束 sector爲BINFS_BLOCK*PAGES_PER_BLOCK，
第三個參數分區的格式爲PART_BINFS，即BINFS格式，
第四個參數指示該分區爲活動分區，fActive = TURE，
第五個參數PART_OPEN_ALWAYS指示如果分區不存在就創建該分區，存在就OPEN該分區，返回分區句柄。
HANDLE BP_OpenPartition(DWORD dwStartSector, DWORD dwNumSectors, DWORD dwPartType, BOOL fActive, DWORD dwCreationFlags)
{
DWORD dwPartIndex;
BOOL fExists;
ASSERT (g_pbMBRSector);
if (!IsValidMBR()) {
DWORD dwFlags = 0;
//fly
RETAILMSG(1, (TEXT("BP_OpenPartition:: dwStartSector=0x%x ,dwNumSectors= 0x%x.,dwPartType = 0x%x/r/n"), dwStartSector, dwNumSectors,dwPartType));
if (dwCreationFlags == PART_OPEN_EXISTING) {
RETAILMSG(1, (TEXT("OpenPartition: Invalid MBR. Cannot open existing partition 0x%x./r/n"), dwPartType));
return INVALID_HANDLE_VALUE;
}
RETAILMSG(1, (TEXT("OpenPartition: Invalid MBR. Formatting flash./r/n")));
if (g_FlashInfo.flashType == NOR) {
dwFlags |= FORMAT_SKIP_BLOCK_CHECK;
}
//fly
RETAILMSG(1, (TEXT("BP_LowLevelFormat: g_pbMBRSector=0x%x, g_dwMBRSectorNum= 0x%x./r/n"), *g_pbMBRSector, g_dwMBRSectorNum));
BP_LowLevelFormat (SECTOR_TO_BLOCK(dwStartSector), SECTOR_TO_BLOCK(dwNumSectors), dwFlags);
dwPartIndex = 0;
fExists = FALSE;
}
else {
fExists = GetPartitionTableIndex(dwPartType, fActive, &dwPartIndex);
}
RETAILMSG(1, (TEXT("OpenPartition: Partition Exists=0x%x for part 0x%x./r/n"), fExists, dwPartType));
if (fExists) {
// Partition was found.
if (dwCreationFlags == PART_CREATE_NEW)
return INVALID_HANDLE_VALUE;
if (g_partStateTable[dwPartIndex].pPartEntry == NULL) {
// Open partition. If this is the boot section partition, then file pointer starts after MBR
g_partStateTable[dwPartIndex].pPartEntry = (PPARTENTRY)(g_pbMBRSector + PARTTABLE_OFFSET + sizeof(PARTENTRY)*dwPartIndex);
g_partStateTable[dwPartIndex].dwDataPointer = 0;
}
if ( dwNumSectors > g_partStateTable[dwPartIndex].pPartEntry->Part_TotalSectors )
return CreatePartition (dwStartSector, dwNumSectors, dwPartType, fActive, dwPartIndex);
else
return (HANDLE)&g_partStateTable[dwPartIndex];
}
else {
// If there are already 4 partitions, or creation flag specified OPEN_EXISTING, fail.
if ((dwPartIndex == NUM_PARTS) || (dwCreationFlags == PART_OPEN_EXISTING))
return INVALID_HANDLE_VALUE;
// Create new partition
return CreatePartition (dwStartSector, dwNumSectors, dwPartType, fActive, dwPartIndex);
}
return INVALID_HANDLE_VALUE;
}
進入函數，首先做的事就是檢測MBR的有效性。通過函數IsValidMBR（）實現。
檢測MBR的有效性，首先要知道MBR保存在哪裏，前面說過NANDFLASH的第0 BLOCK，第1 Sector爲主引導扇區，也就是MBR，但是NAND如果被當作啓動芯片，○地址一般被BOOTLOADER代碼佔據，MBR只有放在後面的BLOCK中。所以我把第0 個BLOCK放NBOOT，第1個BLOCK放TOC，第2個BLOCK放EBOOT，第3個BLOCK保留，第4個BLOCK就放MBR。
static BOOL IsValidMBR()
{
// Check to see if the MBR is valid
// MBR block is always located at logical sector 0
g_dwMBRSectorNum = GetMBRSectorNum();
RETAILMSG (1, (TEXT("IsValidMBR: MBR sector = 0x%x/r/n"), g_dwMBRSectorNum));
if ((g_dwMBRSectorNum == INVALID_ADDR) || !FMD_ReadSector (g_dwMBRSectorNum, g_pbMBRSector, NULL, 1)) {
RETAILMSG (1, (TEXT("IsValidMBR-----return FALSE-------------------/r/n")));
return FALSE;
}
return ((g_pbMBRSector[0] == 0xE9) &&
(g_pbMBRSector[1] == 0xfd) &&
(g_pbMBRSector[2] == 0xff) &&
(g_pbMBRSector[SECTOR_SIZE_FS-2] == 0x55) &&
(g_pbMBRSector[SECTOR_SIZE_FS-1] == 0xAA));
}
IsValidMBR()實現的第一行就是給全局變量g_dwMBRSectorNum 賦值，顯而易見，g_dwMBRSectorNum就是指示保存MBR的那個Sector了。
g_dwMBRSectorNum = GetMBRSectorNum(); //是獲得保存MBR的那個Sector
static DWORD GetMBRSectorNum ()
{
DWORD dwBlockNum = 3, dwSector = 0;
SectorInfo si;
while (dwBlockNum < g_FlashInfo.dwNumBlocks) {
if (!IS_BLOCK_UNUSABLE (dwBlockNum)) {
dwSector = dwBlockNum * g_FlashInfo.wSectorsPerBlock;
if (!FMD_ReadSector (dwSector, NULL, &si, 1)) {
RETAILMSG(1, (TEXT("GetMBRSectorNum: Could not read sector 0x%x./r/n"), dwSector));
return INVALID_ADDR;
}
// Check to see if logical sector number is 0
if (si.dwReserved1 == 0) {
//RETAILMSG(1,(TEXT("dwBlockNum=%d/r/n"),dwBlockNum));
return dwSector;
}
}
dwBlockNum++;
}
return INVALID_ADDR;
}
這裏dwBlockNum直接給了個3，因爲NBOOT，TOC，EBOOT已經把前三個BLOCK用了。所以MBR的選擇直接排除了前三個BLOCK了。
#define IS_BLOCK_UNUSABLE(blockID) ((FMD_GetBlockStatus (blockID) & (BLOCK_STATUS_BAD|BLOCK_STATUS_RESERVED)) > 0)
然後確定BLOCK是否可使用的BLOCK，最後通si.dwReserved1 == 0來判斷是不是選擇這個Sector來保存MBR。
IsValidMBR（）中還有一個重要的結構就是g_pbMBRSector數組，它就是MBR了。
函數返回時，MBR必須符合下列記錄。
return ((g_pbMBRSector[0] == 0xE9) &&
(g_pbMBRSector[1] == 0xfd) &&
(g_pbMBRSector[2] == 0xff) &&
(g_pbMBRSector[SECTOR_SIZE_FS-2] == 0x55) &&
(g_pbMBRSector[SECTOR_SIZE_FS-1] == 0xAA));
可以看到只有開始三個字節爲0XE9,FD,FF，當然，還有熟悉的結束標誌符0X55AA。
如果沒有檢測到MBR，則先對NANDFLASH進行低級格式化。BP_LowLevelFormat (SECTOR_TO_BLOCK(dwStartSector), SECTOR_TO_BLOCK(dwNumSectors), dwFlags);再創建分區，CreatePartition (dwStartSector, dwNumSectors, dwPartType, fActive, dwPartIndex);。
BOOL BP_LowLevelFormat(DWORD dwStartBlock, DWORD dwNumBlocks, DWORD dwFlags)
{
dwNumBlocks = min (dwNumBlocks, g_FlashInfo.dwNumBlocks);
RETAILMSG(1,(TEXT("fly::Enter LowLevelFormat [0x%x, 0x%x]./r/n"), dwStartBlock,dwNumBlocks));// dwStartBlock + dwNumBlocks - 1));
// Erase all the flash blocks.
if (!EraseBlocks(dwStartBlock, dwNumBlocks, dwFlags))
return(FALSE);
// Determine first good starting block
while (IS_BLOCK_UNUSABLE (dwStartBlock) && dwStartBlock < g_FlashInfo.dwNumBlocks) {
dwStartBlock++;
}
if (dwStartBlock >= g_FlashInfo.dwNumBlocks) {
RETAILMSG(1,(TEXT("BP_LowLevelFormat: no good blocks/r/n")));
return FALSE;
}
// MBR goes in the first sector of the starting block. This will be logical sector 0.
g_dwMBRSectorNum = dwStartBlock * g_FlashInfo.wSectorsPerBlock;
RETAILMSG(1,(TEXT("fly:g_dwMBRSectorNum=%d/r/n"),g_dwMBRSectorNum));
// Create an MBR.
CreateMBR();
return(TRUE);
}
在對NANDFLASH進行低格時，主要對壞塊的處理。if (!EraseBlocks(dwStartBlock, dwNumBlocks, dwFlags))檢測每一個Sector，每個BLOCK只要有一個Sector不能讀寫這個塊都會被處理成壞塊，這樣才能保證系統的穩定性。在函數的最後調用了 CreateMBR();來創建一個MBR。static BOOL CreateMBR()
{
// This, plus a valid partition table, is all the CE partition manager needs to recognize
// the MBR as valid. It does not contain boot code.
memset (g_pbMBRSector, 0xff, g_FlashInfo.wDataBytesPerSector);
g_pbMBRSector[0] = 0xE9;
g_pbMBRSector[1] = 0xfd;
g_pbMBRSector[2] = 0xff;
g_pbMBRSector[SECTOR_SIZE_FS-2] = 0x55;
g_pbMBRSector[SECTOR_SIZE_FS-1] = 0xAA;
// Zero out partition table so that mspart treats entries as empty.
memset (g_pbMBRSector+PARTTABLE_OFFSET, 0, sizeof(PARTENTRY) * NUM_PARTS);
return WriteMBR();
} 當然。因爲還沒有進行分區，這裏寫入的MBR分區表部分是空的。static BOOL WriteMBR()
{
DWORD dwMBRBlockNum = g_dwMBRSectorNum / g_FlashInfo.wSectorsPerBlock;
//dwMBRBlockNum = 1 ;
RETAILMSG(1, (TEXT("WriteMBR: MBR block = 0x%x,g_dwMBRSectorNum = 0x%x./r/n"), dwMBRBlockNum,g_dwMBRSectorNum));
memset (g_pbBlock, 0xff, g_dwDataBytesPerBlock);
memset (g_pSectorInfoBuf, 0xff, sizeof(SectorInfo) * g_FlashInfo.wSectorsPerBlock);
// No need to check return, since a failed read means data hasn't been written yet.
ReadBlock (dwMBRBlockNum, g_pbBlock, g_pSectorInfoBuf);
if (!FMD_EraseBlock (dwMBRBlockNum)) {
RETAILMSG (1, (TEXT("CreatePartition: error erasing block 0x%x/r/n"), dwMBRBlockNum));
return FALSE;
}
memcpy (g_pbBlock + (g_dwMBRSectorNum % g_FlashInfo.wSectorsPerBlock) * g_FlashInfo.wDataBytesPerSector, g_pbMBRSector, g_FlashInfo.wDataBytesPerSector);
g_pSectorInfoBuf->bOEMReserved &= ~OEM_BLOCK_READONLY;
g_pSectorInfoBuf->wReserved2 &= ~SECTOR_WRITE_COMPLETED;
g_pSectorInfoBuf->dwReserved1 = 0;
RETAILMSG(1, (TEXT("fly::WriteMBR: MBR block = 0x%x./r/n"), dwMBRBlockNum));
if (!WriteBlock (dwMBRBlockNum, g_pbBlock, g_pSectorInfoBuf)) {
RETAILMSG (1, (TEXT("CreatePartition: could not write to block 0x%x/r/n"), dwMBRBlockNum));
return FALSE;
}
return TRUE;
}
在WriteMBR()函數中，就寫入了判斷MBR 的一些標誌到BLOCK， g_pSectorInfoBuf->bOEMReserved &= ~OEM_BLOCK_READONLY;
g_pSectorInfoBuf->wReserved2 &= ~SECTOR_WRITE_COMPLETED;
g_pSectorInfoBuf->dwReserved1 = 0;
Wince系統啓動時，具體是NANDFLASH驅動加載成功後，MOUNT文件系統到NANDFLASH之前，也會通過讀取這些SectorInfo來得到MBR 保存的BLOCK，進而讀取MBR，獲得分區信息，從而把各分區MOUNT到相應文件系統。格式化完成，MBR也寫入成功後就可以開始新建分區了。
/* CreatePartition
*
* Creates a new partition. If it is a boot section partition, then it formats
* flash.
*
* ENTRY
* dwStartSector - Logical sector to start the partition. NEXT_FREE_LOC if
* none specified.
* dwNumSectors - Number of logical sectors of the partition. USE_REMAINING_SPACE
* to indicate to take up the rest of the space on the flash for that partition.
* dwPartType - Type of partition to create.
* fActive - TRUE indicates to create the active partition. FALSE for
* inactive.
* dwPartIndex - Index of the partition entry on the MBR
*
* EXIT
* Handle to the partition on success. INVALID_HANDLE_VALUE on error.
*/
static HANDLE CreatePartition (DWORD dwStartSector, DWORD dwNumSectors, DWORD dwPartType, BOOL fActive, DWORD dwPartIndex)
{
DWORD dwBootInd = 0;
RETAILMSG(1, (TEXT("CreatePartition: Enter CreatePartition for 0x%x./r/n"), dwPartType));
if (fActive)
dwBootInd |= PART_IND_ACTIVE;
if (dwPartType == PART_BOOTSECTION || dwPartType == PART_BINFS || dwPartType == PART_XIP)
dwBootInd |= PART_IND_READ_ONLY;
// If start sector is invalid, it means find next free sector
if (dwStartSector == NEXT_FREE_LOC) {
dwStartSector = FindFreeSector();
if (dwStartSector == INVALID_ADDR) {
RETAILMSG(1, (TEXT("CreatePartition: can't find free sector./r/n")));
return INVALID_HANDLE_VALUE;
}
// Start extended partition on a block boundary
if ((dwPartType == PART_EXTENDED) && (dwStartSector % g_FlashInfo.wSectorsPerBlock)) {
dwStartSector = (dwStartSector / g_FlashInfo.wSectorsPerBlock + 1) * g_FlashInfo.wSectorsPerBlock;
}
}
// If num sectors is invalid, fill the rest of the space up
if (dwNumSectors == USE_REMAINING_SPACE) {
DWORD dwLastLogSector = LastLogSector();
if (dwLastLogSector == INVALID_ADDR)
return INVALID_HANDLE_VALUE;
// Determine the number of blocks to reserve for the FAL compaction when creating an extended partition.
DWORD dwReservedBlocks = g_FlashInfo.dwNumBlocks / PERCENTAGE_OF_MEDIA_TO_RESERVE;
if((dwReservedBlocks = g_FlashInfo.dwNumBlocks / PERCENTAGE_OF_MEDIA_TO_RESERVE) < MINIMUM_FLASH_BLOCKS_TO_RESERVE) {
dwReservedBlocks = MINIMUM_FLASH_BLOCKS_TO_RESERVE;
}
dwNumSectors = dwLastLogSector - dwStartSector + 1 - dwReservedBlocks * g_FlashInfo.wSectorsPerBlock;
}
if (!AreSectorsFree (dwStartSector, dwNumSectors)){
RETAILMSG (1, (TEXT("fly:::::CreatePartition: sectors [0x%x, 0x%x] requested are out of range or taken by another partition/r/n"), dwStartSector, dwNumSectors));
return INVALID_HANDLE_VALUE;
}
RETAILMSG(1, (TEXT("CreatePartition: Start = 0x%x, Num = 0x%x./r/n"), dwStartSector, dwNumSectors));
AddPartitionTableEntry (dwPartIndex, dwStartSector, dwNumSectors, (BYTE)dwPartType, (BYTE)dwBootInd);
if (dwBootInd & PART_IND_READ_ONLY) {
if (!WriteLogicalNumbers (dwStartSector, dwNumSectors, TRUE)) {
RETAILMSG(1, (TEXT("CreatePartition: can't mark sector info./r/n")));
return INVALID_HANDLE_VALUE;
}
}
if (!WriteMBR())
return INVALID_HANDLE_VALUE;
g_partStateTable[dwPartIndex].pPartEntry = (PPARTENTRY)(g_pbMBRSector + PARTTABLE_OFFSET + sizeof(PARTENTRY)*dwPartIndex);
g_partStateTable[dwPartIndex].dwDataPointer = 0;
return (HANDLE)&g_partStateTable[dwPartIndex];
}
如果第二個參數爲－1，則視爲將餘下的所有空間劃爲一個分區。LastLogSector();函數獲得最後一個邏輯Sector。static DWORD LastLogSector()
{
if (g_dwLastLogSector) {
return g_dwLastLogSector;
}
DWORD dwMBRBlock = g_dwMBRSectorNum / g_FlashInfo.wSectorsPerBlock;
DWORD dwUnusableBlocks = dwMBRBlock;
for (DWORD i = dwMBRBlock; i < g_FlashInfo.dwNumBlocks; i++) {
if (IS_BLOCK_UNUSABLE (i))
dwUnusableBlocks++;
}
g_dwLastLogSector = (g_FlashInfo.dwNumBlocks - dwUnusableBlocks) * g_FlashInfo.wSectorsPerBlock - 1;
RETAILMSG(1, (TEXT("fly:::LastLogSector: Last log sector is: 0x%x./r/n"), g_dwLastLogSector));
return g_dwLastLogSector;
}
即g_dwLastLogSector = (g_FlashInfo.dwNumBlocks - dwUnusableBlocks) * g_FlashInfo.wSectorsPerBlock - 1;//（NAND 的BLOCK總數 – MBR保存的那個BLOCK）* 每個BLOCK的Sector數 – 保存MBR的那個Sector。得到的就是從MBR那個Sector之後的所有Sector，即邏輯大小。
AreSectorsFree (dwStartSector, dwNumSectors)函數判斷參數提供的起始Sector和個數有沒有超出來NAND的界限，或者邏輯分區的界限。
重頭戲開始了。通過AddPartitionTableEntry (dwPartIndex, dwStartSector, dwNumSectors, (BYTE)dwPartType, (BYTE)dwBootInd); 準備分區信息寫入分區表。
/* AddPartitionTableEntry
*
* Generates the partition entry for the partition table and copies the entry
* into the MBR that is stored in memory.
*
*
* ENTRY
* entry - index into partition table
* startSector - starting logical sector
* totalSectors - total logical sectors
* fileSystem - type of partition
* bootInd - byte in partition entry that stores various flags such as
* active and read-only status.
*
* EXIT
*/
static void AddPartitionTableEntry(DWORD entry, DWORD startSector, DWORD totalSectors, BYTE fileSystem, BYTE bootInd)
{
PARTENTRY partentry = {0};
Addr startAddr;
Addr endAddr;
ASSERT(entry < 4);
// no checking with disk info and start/total sectors because we allow
// bogus partitions for testing purposes
// initially known partition table entry
partentry.Part_BootInd = bootInd;
partentry.Part_FileSystem = fileSystem;
partentry.Part_StartSector = startSector;
partentry.Part_TotalSectors = totalSectors;
// logical block addresses for the first and final sector (start on the second head)
startAddr.type = LBA;
startAddr.lba = partentry.Part_StartSector;
endAddr.type = LBA;
endAddr.lba = partentry.Part_StartSector + partentry.Part_TotalSectors-1;
// translate the LBA addresses to CHS addresses
startAddr = LBAtoCHS(&g_FlashInfo, startAddr);
endAddr = LBAtoCHS(&g_FlashInfo, endAddr);
// starting address
partentry.Part_FirstTrack = (BYTE)(startAddr.chs.cylinder & 0xFF);
partentry.Part_FirstHead = (BYTE)(startAddr.chs.head & 0xFF);
// lower 6-bits == sector, upper 2-bits = cylinder upper 2-bits of 10-bit cylinder #
partentry.Part_FirstSector = (BYTE)((startAddr.chs.sector & 0x3F) | ((startAddr.chs.cylinder & 0x0300) >> 2));
// ending address:
partentry.Part_LastTrack = (BYTE)(endAddr.chs.cylinder & 0xFF);
partentry.Part_LastHead = (BYTE)(endAddr.chs.head & 0xFF);
// lower 6-bits == sector, upper 2-bits = cylinder upper 2-bits of 10-bit cylinder #
partentry.Part_LastSector = (BYTE)((endAddr.chs.sector & 0x3F) | ((endAddr.chs.cylinder & 0x0300) >> 2));
memcpy(g_pbMBRSector+PARTTABLE_OFFSET+(sizeof(PARTENTRY)*entry), &partentry, sizeof(PARTENTRY));
}
這裏面的地址信息是一種叫CHS(Cyinder/Head/Sector)的地址。eboot中有將邏輯地址LBS(Logical Block Addr)與這種地址互相轉換的函數LBAtoCHS,CHSToLBA。
Addr LBAtoCHS(FlashInfo *pFlashInfo, Addr lba)
{
Addr chs;
DWORD tmp = pFlashInfo->dwNumBlocks * pFlashInfo->wSectorsPerBlock;
chs.type = CHS;
chs.chs.cylinder = (WORD)(lba.lba / tmp); // 柱面,應該始終是0
tmp = lba.lba % tmp;
chs.chs.head = (WORD)(tmp / pFlashInfo->wSectorsPerBlock); // 塊地址
chs.chs.sector = (WORD)((tmp % pFlashInfo->wSectorsPerBlock) + 1); // 扇區+1
return chs;
}
Addr CHStoLBA(FlashInfo *pFlashInfo, Addr chs)
{
Addr lba;
lba.type = LBA;
lba.lba = ((chs.chs.cylinder * pFlashInfo->dwNumBlocks + chs.chs.head)
* pFlashInfo->wSectorsPerBlock)+ chs.chs.sector - 1;
return lba;
}
如果分區的格式有隻讀屬性，則通過WriteLogicalNumbers（）函數寫分區的Sectorinfo，把這部分空間保護起來。
static BOOL WriteLogicalNumbers (DWORD dwStartSector, DWORD dwNumSectors, BOOL fReadOnly)
{
DWORD dwNumSectorsWritten = 0;
DWORD dwPhysSector = Log2Phys (dwStartSector);
DWORD dwBlockNum = dwPhysSector / g_FlashInfo.wSectorsPerBlock;
DWORD dwOffset = dwPhysSector % g_FlashInfo.wSectorsPerBlock;
while (dwNumSectorsWritten < dwNumSectors) {
// If bad block, move to the next block
if (IS_BLOCK_UNUSABLE (dwBlockNum)) {
dwBlockNum++;
continue;
}
memset (g_pbBlock, 0xff, g_dwDataBytesPerBlock);
memset (g_pSectorInfoBuf, 0xff, sizeof(SectorInfo) * g_FlashInfo.wSectorsPerBlock);
// No need to check return, since a failed read means data hasn't been written yet.
ReadBlock (dwBlockNum, g_pbBlock, g_pSectorInfoBuf);
if (!FMD_EraseBlock (dwBlockNum)) {
return FALSE;
}
DWORD dwSectorsToWrite = g_FlashInfo.wSectorsPerBlock - dwOffset;
PSectorInfo pSectorInfo = g_pSectorInfoBuf + dwOffset;
// If this is the last block, then calculate sectors to write if there isn't a full block to update
if ((dwSectorsToWrite + dwNumSectorsWritten) > dwNumSectors)
dwSectorsToWrite = dwNumSectors - dwNumSectorsWritten;
for (DWORD iSector = 0; iSector < dwSectorsToWrite; iSector++, pSectorInfo++, dwNumSectorsWritten++) {
// Assert read only by setting bit to 0 to prevent wear-leveling by FAL
if (fReadOnly)
pSectorInfo->bOEMReserved &= ~OEM_BLOCK_READONLY;
// Set to write completed so FAL can map the sector
pSectorInfo->wReserved2 &= ~SECTOR_WRITE_COMPLETED;
// Write the logical sector number
pSectorInfo->dwReserved1 = dwStartSector + dwNumSectorsWritten;
}
if (!WriteBlock (dwBlockNum, g_pbBlock, g_pSectorInfoBuf))
return FALSE;
dwOffset = 0;
dwBlockNum++;
}
return TRUE;
}
這就是爲什麼系統啓動後，我們無法寫入文件的BINFS文件系統格式分區的原因了。而FAT格式就可以。最後調用WriteMBR()完全MBR的寫入，分區完畢。
讓我們繼續回到BP_OpenPartition函數中，如果從一開始IsValidMBR()就檢測到有效的MBR，GetPartitionTableIndex(dwPartType, fActive, &dwPartIndex);獲得分區表。和dwPartIndex分區表的索引號。
static BOOL GetPartitionTableIndex (DWORD dwPartType, BOOL fActive, PDWORD pdwIndex)
{
PPARTENTRY pPartEntry = (PPARTENTRY)(g_pbMBRSector + PARTTABLE_OFFSET);
DWORD iEntry = 0;
for (iEntry = 0; iEntry < NUM_PARTS; iEntry++, pPartEntry++) {
if ((pPartEntry->Part_FileSystem == dwPartType) && (((pPartEntry->Part_BootInd & PART_IND_ACTIVE) != 0) == fActive)) {
*pdwIndex = iEntry;
return TRUE;
}
if (!IsValidPart (pPartEntry)) {
*pdwIndex = iEntry;
return FALSE;
}
}
return FALSE;
}
重要結構：PARTENTRY
// end of master boot record contains 4 partition entries
typedef struct _PARTENTRY {
BYTE Part_BootInd; // If 80h means this is boot partition
BYTE Part_FirstHead; // Partition starting head based 0
BYTE Part_FirstSector; // Partition starting sector based 1
BYTE Part_FirstTrack; // Partition starting track based 0
BYTE Part_FileSystem; // Partition type signature field
BYTE Part_LastHead; // Partition ending head based 0
BYTE Part_LastSector; // Partition ending sector based 1
BYTE Part_LastTrack; // Partition ending track based 0
DWORD Part_StartSector; // Logical starting sector based 0
DWORD Part_TotalSectors; // Total logical sectors in partition
} PARTENTRY;
分區表就是通過這個結構寫入MBR，起始地址，分區大小，分區格式，對應結構寫入MBR所在的Sector就可以了。在檢測有效分區時static BOOL IsValidPart (PPARTENTRY pPartEntry)
{
return (pPartEntry->Part_FileSystem != 0xff) && (pPartEntry->Part_FileSystem != 0);
}
就是通過對分區表文件系統格式的判斷了。
把NAND後面的空間，全部分爲一個FAT格式的分區。
//
// create extended partition in whatever is left
//
hPartEx = BP_OpenPartition( (NK_START_BLOCK+1+BINFS_BLOCK) * PAGES_PER_BLOCK,
NEXT_FREE_LOC, // (1024 - (NK_START_BLOCK+1+SECTOR_TO_BLOCK_SIZE(FILE_TO_SECTOR_SIZE(dwBINFSPartLength)))) * PAGES_PER_BLOCK,
PART_DOS32,
TRUE,
PART_OPEN_ALWAYS);
if (hPartEx == INVALID_HANDLE_VALUE )
{
EdbgOutputDebugString("*** WARN: StoreImageToBootMedia: Failed to open/create Extended partition ***/r/n");
}