initial fs code, readme and gitignore changes, etc

.gitignore

@@ -1,3 +1,4 @@
 obj/
 foxdos
 kernel.map
+*.swp

README.md

@@ -1 +1,3 @@
 # foxdos
+
+WIP MS-DOS reimplementation for 386+ machines

doc/README.md

@@ -0,0 +1,7 @@
+# foxdos docs
+
+most of the documentation exists in the form of code comments at the moment
+
+## mothfs
+
+`tool/inc/fs.h` contains the majority of documentation for the fs. eventually one of us will probably write a more readable version in md or html

src/disk.s

@@ -32,10 +32,11 @@ read_sector:
 	push bx
 	push es
 .retry:
-	mov es, SECTOR_SEG
+	mov bx, SECTOR_SEG
+	mov es, bx
 	mov bx, SECTOR_ADDR
 	call lba2chs
-	mov ax 0x0201
+	mov ax, 0x0201
 	int 0x13
 	jc .retry
 	pop es

src/int21/2.s

@@ -12,6 +12,8 @@ setint:
 	xor ah, ah
 	shl ax, 2
 	mov di, ax
+	mov ax, word [callerds]
+	mov ds, ax
 	xor ax, ax
 	push es
 	mov es, ax

tool/build

@@ -0,0 +1,9 @@
+for i in xxd; do which $i || exit; done
+
+CC='cc -O3 -Iinc'
+
+for i in bin2h; do [ ! -f "$i" ] && $CC "$i.c" -o "$i"; done
+
+[ ! -f mkmothfs ] && nasm mfs_hdr.s && \
+			xxd -i mfs_hdr > inc/mfs_hdr.h && \
+			$CC mkmothfs.c

tool/inc/fs.h

@@ -0,0 +1,58 @@
+typedef struct {
+	uint32_t jmp;		// used to jump past the header
+	uint8_t magic[7];	// 'MOTHFS\0'
+	uint8_t version;	// currently fs version 0
+	uint32_t size;		// partition size in sectors - sectors always 512b
+				// this means the max size is 'only' 2tb but i would
+				// be surprised if anyone managed to use 2tb in dos
+
+	uint32_t offset;	// offset of partition from start of disk
+	uint8_t volname[15];	// name of partition
+	uint8_t reserved;	// number of sectors reserved for boot code. these
+				// are stored immediately following this header
+
+	uint32_t abm;		// number of sectors reserved for the allocation
+				// bitmap. these immediately follow the boot code
+				// sectors. the root directory is stored in the first
+				// non-reserved sector
+	
+	uint8_t bootcode[470];
+	uint16_t signature;	// 0xAA55 as usual to make it directly bootable
+} mothfs_header; // 512 bytes
+
+typedef struct {
+	uint32_t sector;	// sector offset relative to the partition, not the disk
+	uint32_t length;	// number of consecutive sectors to address
+} ptrlen; // 8 bytes
+
+typedef struct {
+	uint8_t type;		// 0 - file
+				// 1 - directory
+
+	uint8_t perms[3];	// unused in foxdos. good for alignment. top bit of
+				// each nibble must be zero
+
+	uint32_t ext;		// undefined in version 0 - contains uid, gid, data
+				// for other file types, long filename, etc
+
+	uint8_t name[8];	// filename
+	uint8_t ext[3];		// extension
+	uint8_t lfn;		// size of long filename - must be zero in version 0
+				// this is on par with most filesystems
+
+	uint16_t freebytes;	// number of bytes unused in last sector of file data
+	uint16_t pad;
+	
+	uint32_t data[122];
+
+	// for files - `data` is 61 `ptrlen`s. if not all 60 are used, it must be null
+	// terminated by setting ptrlen.sector to zero. if there is no terminator,
+	// data[60].sector points to a sector containing 64 more `ptrlen`s. if there is
+	// no terminator in that sector, the last `ptrlen` points to another sector of
+	// identical layout. this continues until a sector with a terminator is found
+
+	// for directories - `data` is 122 sector offsets. if not all 121 are used, it
+	// must be null terminated. if there is no terminator, data[121] points to a
+	// sector containing 128 more sector offsets. the rules for this are similar
+	// enough to how files work that i do not want to write it out again
+} mothfs_file; // 512 bytes

tool/mfs_hdr.s

@@ -0,0 +1,73 @@
+; TODO implement boot via chs for old bioses (even ones
+; as new as 1996 lack support for lba via bios call)
+[bits 16]
+[org 0x7C00]
+
+jmp entry
+times 4 - ($-$$) db 0
+
+db "MOTHFS",0
+db 0
+sz:	dd 32768	; 32768 * 512 = 16mb disk image
+off:	dd 1		; immediately follows mbr
+	db "mkmothfs",0,0,0,0,0,0,0
+rsv:	db 127		; 64kb of boot code
+abm:	dd 4096		; 16mb/(512*8)
+
+entry:
+	push cs
+	pop ds
+	push dx
+
+	; enable a20 a few different ways
+	in al, 0xEE
+
+	; bios call
+	mov ax, 0x2401	; l is real
+	int 0x15
+
+	; fast a20 gate
+	in al, 0x92
+	or al, 2
+	out 0x92, al
+
+	mov eax, [off]
+	mov dword [dapw], eax
+
+	; check for lba support
+	mov ah, 0x41
+	mov bx, 0x55AA
+	int 0x13	; dl is drive number - mbr should pass this value
+	jc .nde
+	shr cx, 2	; wikipedia says bit 1 is disk packet support
+	jnc .nde
+
+	; load kernel flat binary into hma using lba
+	pop dx
+	mov ah, 0x42
+	mov si, dap
+	int 0x13
+
+	; jump to FFFF:0010, the start of HMA. this limits the kernel
+	; size to 65520 bytes but we are actually loading 496 bytes
+	; less than that and even that should be more than enough for
+	; foxdos and any more would probably blow up some garbage bios
+	mov ax, 0xFFFF
+	push ax
+	mov ax, 16
+	push ax
+	retf
+	
+.nde:	mov eax, [sz]
+	add eax, [off]
+	cmp eax, 0xFB0400 ; max chs sectors
+	jg $		; too big to use chs
+	jmp $		; TODO load via chs
+
+dap:	dw 0x10		; size of disk packet
+	dw 127		; foxdos will always load 127 segments
+	dw 16, 0xFFFF	; offset:segment to start of HMA - foxdos loads high
+dapw:	dd 0, 0
+
+times 510 - ($-$$) db 0
+dw 0xAA55

tool/mkmothfs.c

@@ -0,0 +1,10 @@
+#include <stdint.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+#include <mfs_hdr.h>
+
+int main(int argc, char** argv) {
+	if(argc < 100) return !!printf("need arguments: ?\n");
+	
+}