Implement reading of partition offset and size

kernel/diskio.asm

@@ -14,11 +14,16 @@ disk_chs: ; DL, DH, CL, CH for int 13h CHS functions
 disk_dap: ; disk access packet for int 13h EBIOS functions
 	resb 0x10
 
-disk_tracks: ; heads * spt
+disk_spc: ; sectors per cylinder = heads * spt
 	resw 1
 disk_spt:
 	resb 1
 
+part_offset:
+	resd 1
+part_size:
+	resd 1
+
 	; Disk access packet for EBIOS extensions
 dapps:	equ 0 ; byte packet size
 dapnum: equ 2 ; word number of sectors to transfer
@@ -53,22 +58,42 @@ select:	mov byte [disk_current], 0xFF
 	mov bx, 0x55AA
 	int 0x13
 	test cx, 1
-	jz .nolba
+	jz select_hdd
 	cmp bx, 0xAA55
-	jnz .nolba
+	jnz select_hdd
 	mov byte [lba_supported], 1
-.nolba:	call seek_zero
+	jmp select_hdd
-	ret
 
 select_floppy:
-	xor dx, dx
+	call seek_zero
-	xor ax, ax
-	call seek
 	call read
+	; load disk geometry
 	mov ax, [disk_buffer+0x0B+bpb_spt]
 	mov [disk_spt], ax
 	mul word [disk_buffer+0x0B+bpb_nos]
-	mov [disk_tracks], ax
+	mov [disk_spc], ax
+	; set partition size
+	; we dont rely on the 'total sectors' given in the BPB
+	; instead, we assume maximum cylinder
+	; 1023 is the maximum encodable for int 13h
+	mov di, 1023
+	mul di
+	mov [part_size], ax
+	mov [part_size+2], dx
+	; set partition offset to zero
+	xor ax, ax
+	mov [part_offset], ax
+	mov [part_offset+2], ax
+	ret
+
+select_hdd:
+	call seek_zero
+	call read
+	mov bx, disk_buffer+0x1BE
+	lea si, [bx+8]
+	lea di, [part_offset]
+	mov cx, 4
+	rep movsw
 	ret
 
 	; Set absolute sector number
@@ -79,7 +104,7 @@ seek:	push ax
 	jz seek_zero
 
 	; dx:ax = lba
-	div word [disk_tracks]
+	div word [disk_spc]
 	xchg ax, dx
 	; dx = cylinder, ax = head * spt + sector
 	div byte [disk_spt]
@@ -98,8 +123,14 @@ seek:	push ax
 	ret
 
 seek_zero:
+	; set chs data to first sector
 	mov byte [disk_chs+1], 0
 	mov word [disk_chs+2], 1
+	; set lba data to first sector
+	lea di, [disk_dap+dapsec]
+	mov cx, 4
+	xor ax, ax
+	rep stosw
 	ret
 
 	; Read a sector into buffer