ext2.asm

一个类似windows

Done:
		mov al,0dh
		call PutCharsCallBios
		mov al,0ah
		call PutCharsCallBios
        retn



msgDiskError		db 'Disk error',0
; Sorry, need the space...
;msgAnyKey			db 'Press any key to restart',0
msgAnyKey			db 'Press any key',0

        times 509-($-$$) db 0   ; Pad to 509 bytes

BootPartition			db 0

        dw 0aa55h       ; BootSector signature
        

; End of bootsector
;
; Now starts the extra boot code that we will store
; at sector 1 on a EXT2 volume



LoadRootDirectory:

		mov  eax,EXT2_ROOT_INO			; Put the root directory inode number in EAX
		call Ext2ReadInode				; Read in the inode

		; Point ES:DI to the inode structure at 6000:8000
		push WORD 6000h
		pop  es
		mov  di,8000h
		push di
		push es							; Save these for later

		; Get root directory size from inode structure
		mov  eax,DWORD [es:di+4]
		push eax

		; Now that the inode has been read in load
		; the root directory file data to 0000:8000
		call Ext2ReadEntireFile

		; Since the root directory was loaded to 0000:8000
		; then add 8000h to the root directory's size
		pop  eax
		mov  edx,8000h					; Set EDX to the current offset in the root directory
		add  eax,edx					; Initially add 8000h to the size of the root directory

SearchRootDirectory:
		push edx						; Save current offset in root directory
		push eax						; Save the size of the root directory

		; Now we have to convert the current offset
		; in the root directory to a SEGMENT:OFFSET pair
		mov  eax,edx
		xor  edx,edx
		mov  ecx,16
		div  ecx						; Now AX:DX has segment & offset
		mov  es,ax
		mov  di,dx
		push di							; Save the start of the directory entry
		add  di,byte 8					; Add the offset to the filename
		mov  si,filename
		mov  cl,11
		rep  cmpsb						; Compare the file names
		pop  di
		pop  eax
		pop  edx
		jz   FoundFile

		; Nope, didn't find it in this entry, keep looking
		movzx ecx,WORD [es:di+4]
		add   edx,ecx

		; Check to see if we have reached the
		; end of the root directory
		cmp  edx,eax
		jb   SearchRootDirectory
		jmp  PrintFileNotFound

FoundFile:
		mov  eax,[es:di]				; Get inode number from directory entry
		call Ext2ReadInode				; Read in the inode

		; Point ES:DI to the inode structure at 6000:8000
		pop  es
		pop  di							; These were saved earlier

		mov  cx,[es:di]					; Get the file mode so we can make sure it's a regular file
		and  ch,EXT2_S_IFMT				; Mask off everything but the file type
		cmp  ch,EXT2_S_IFREG			; Make sure it's a regular file
		je   LoadFreeLoader
		jmp  PrintRegFileError

LoadFreeLoader:
        mov  si,msgLoading				; "Loading FreeLoader..." message
        call PutChars					; Display it

		call Ext2ReadEntireFile			; Read freeldr.sys to 0000:8000

        mov  dl,[BYTE bp+BootDrive]
		mov  dh,[BYTE bp+BootPartition]
        push byte 0						; We loaded at 0000:8000
        push WORD 8000h					; We will do a far return to 0000:8000h
        retf							; Transfer control to FreeLoader





; Reads ext2 file data into [0000:8000]
; This function assumes that the file's
; inode has been read in to 6000:8000 *and*
; ES:DI points to 6000:8000
; This will load all the blocks up to
; and including the double-indirect pointers.
; This should be sufficient because it
; allows for ~64MB which is much bigger
; than we need for a boot loader.
Ext2ReadEntireFile:

		; Reset the load segment
		mov  WORD [BYTE bp+Ext2ReadEntireFileLoadSegment],800h

		; Now we must calculate how
		; many blocks to read in
		; We will do this by rounding the
		; file size up to the next block
		; size and then dividing by the block size
		mov  eax,DWORD [BYTE bp+Ext2BlockSizeInBytes]		; Get the block size in bytes
		push eax
		dec  eax											; Ext2BlockSizeInBytes -= 1
		add  eax,DWORD [es:di+4]							; Add the file size
		xor  edx,edx
		pop  ecx											; Divide by the block size in bytes
		div  ecx											; EAX now contains the number of blocks to load
		push eax

		; Make sure the file size isn't zero
		cmp  eax,byte 0
		jnz  Ext2ReadEntireFile2
		jmp  PrintFileSizeError

Ext2ReadEntireFile2:
		; Save the indirect & double indirect pointers
		mov  edx,DWORD [es:di+0x58]							; Get indirect pointer
		mov  [BYTE bp+Ext2InodeIndirectPointer],edx			; Save indirect pointer
		mov  edx,DWORD [es:di+0x5c]							; Get double indirect pointer
		mov  [BYTE bp+Ext2InodeDoubleIndirectPointer],edx	; Save double indirect pointer

		; Now copy the direct pointers to 7000:0000
		; so that we can call Ext2ReadDirectBlocks
		push ds												; Save DS
		push es
		push WORD 7000h
		pop  es
		pop  ds
		mov  si,8028h
		xor  di,di											; DS:SI = 6000:8028 ES:DI = 7000:0000
		mov  cx,24											; Moving 24 words of data
		rep  movsw
		pop  ds												; Restore DS

		; Now we have all the block pointers in the
		; right location so read them in
		pop  eax											; Restore the total number of blocks in this file
		xor  ecx,ecx										; Set the max count of blocks to read to 12
		mov  cl,12											; which is the number of direct block pointers in the inode
		call Ext2ReadDirectBlockList

		; Check to see if we actually have
		; blocks left to read
		cmp  eax,byte 0
		jz   Ext2ReadEntireFileDone

		; Now we have read all the direct blocks in
		; the inode. So now we have to read the indirect
		; block and read all it's direct blocks
		push eax											; Save the total block count
		mov  eax,DWORD [BYTE bp+Ext2InodeIndirectPointer]	; Get the indirect block pointer
		push WORD 7000h
		pop  es
		xor  bx,bx											; Set the load address to 7000:0000
		call Ext2ReadBlock									; Read the block

		; Now we have all the block pointers from the
		; indirect block in the right location so read them in
		pop  eax											; Restore the total block count
		mov  ecx,DWORD [BYTE bp+Ext2PointersPerBlock]		; Get the number of block pointers that one block contains
		call Ext2ReadDirectBlockList

		; Check to see if we actually have
		; blocks left to read
		cmp  eax,byte 0
		jz   Ext2ReadEntireFileDone

		; Now we have read all the direct blocks from
		; the inode's indirect block pointer. So now
		; we have to read the double indirect block
		; and read all it's indirect blocks
		; (whew, it's a good thing I don't support triple indirect blocks)
		mov  [BYTE bp+Ext2BlocksLeftToRead],eax				; Save the total block count
		mov  eax,DWORD [BYTE bp+Ext2InodeDoubleIndirectPointer]	; Get the double indirect block pointer
		push WORD 7800h
		pop  es
		push es												; Save an extra copy of this value on the stack
		xor  bx,bx											; Set the load address to 7000:8000
		call Ext2ReadBlock									; Read the block

		pop  es												; Put 7800h into ES (saved on the stack already)
		xor  di,di

Ext2ReadIndirectBlock:
		mov  eax,DWORD [es:di]								; Get indirect block pointer
		add  di,BYTE 4										; Update DI for next array index
		push es
		push di

		push WORD 7000h
		pop  es
		xor  bx,bx											; Set the load address to 7000:0000
		call Ext2ReadBlock									; Read the indirect block

		; Now we have all the block pointers from the
		; indirect block in the right location so read them in
		mov  eax,DWORD [BYTE bp+Ext2BlocksLeftToRead]		; Restore the total block count
		mov  ecx,DWORD [BYTE bp+Ext2PointersPerBlock]		; Get the number of block pointers that one block contains
		call Ext2ReadDirectBlockList
		mov  [BYTE bp+Ext2BlocksLeftToRead],eax				; Save the total block count
		pop  di
		pop  es

		; Check to see if we actually have
		; blocks left to read
		cmp  eax,byte 0
		jnz  Ext2ReadIndirectBlock

Ext2ReadEntireFileDone:
		ret

; Reads a maximum number of blocks
; from an array at 7000:0000
; and updates the total count
; ECX contains the max number of blocks to read
; EAX contains the number of blocks left to read
; On return:
;  EAX contians the new number of blocks left to read
Ext2ReadDirectBlockList:
		cmp  eax,ecx										; Compare it to the maximum number of blocks to read
		ja   CallExt2ReadDirectBlocks						; If it will take more blocks then just read all of the blocks
		mov  cx,ax											; Otherwise adjust the block count accordingly

CallExt2ReadDirectBlocks:
		sub  eax,ecx										; Subtract the number of blocks being read from the total count
		push eax											; Save the new total count
		call Ext2ReadDirectBlocks
		pop  eax											; Restore the total count
		ret


; Reads a specified number of blocks
; from an array at 7000:0000
; CX contains the number of blocks to read
Ext2ReadDirectBlocks:

		push WORD 7000h
		pop  es
		xor  di,di											; Set ES:DI = 7000:0000

Ext2ReadDirectBlocksLoop:
		mov  eax,[es:di]									; Get direct block pointer from array
		add  di,BYTE 4										; Update DI for next array index

		push cx												; Save number of direct blocks left
		push es												; Save array segment
		push di												; Save array offset
		mov  es,[BYTE bp+Ext2ReadEntireFileLoadSegment]
		xor  bx,bx											; Setup load address for next read

		call Ext2ReadBlock									; Read the block (this updates ES for the next read)

		mov  [BYTE bp+Ext2ReadEntireFileLoadSegment],es		; Save updated ES

		pop  di												; Restore the array offset
		pop  es												; Restore the array segment
		pop  cx												; Restore the number of blocks left

		loop Ext2ReadDirectBlocksLoop

		; At this point all the direct blocks should
		; be loaded and ES (Ext2ReadEntireFileLoadSegment)
		; should be ready for the next read.
		ret



; Displays a file not found error message
; And reboots
PrintFileNotFound:
        mov  si,msgFreeLdr      ; FreeLdr not found message
		jmp short DisplayItAndReboot

; Displays a file size is 0 error
; And reboots
PrintFileSizeError:
        mov  si,msgFileSize     ; Error message
		jmp short DisplayItAndReboot

; Displays a file is not a regular file error
; And reboots
PrintRegFileError:
        mov  si,msgRegFile      ; Error message
DisplayItAndReboot:
        call PutChars           ; Display it
		jmp  Reboot

msgFreeLdr   db 'freeldr.sys not found',0
msgFileSize  db 'File size is 0',0
msgRegFile   db 'freeldr.sys isnt a regular file',0
filename     db 'freeldr.sys'
msgLoading   db 'Loading FreeLoader...',0

        times 1022-($-$$) db 0   ; Pad to 1022 bytes

        dw 0aa55h       ; BootSector signature