From b3df18bb0467268c3385cff9d8d709371c2ef975 Mon Sep 17 00:00:00 2001
From: shikhin <draumr.shikhin@gmail.com>
Date: Sun, 19 Mar 2023 20:09:35 +0530
Subject: [PATCH] Switch from read_sectors to modify_sectors; return dirent in
 open_file

---
 extract_symbols.py |  2 +-
 ponydos.asm        | 38 ++++++++++++++++++--------------------
 ponydos_static.inc |  1 +
 shell.asm          |  3 ++-
 4 files changed, 22 insertions(+), 22 deletions(-)

diff --git a/extract_symbols.py b/extract_symbols.py
index b0d64cf..ecd1e5e 100644
--- a/extract_symbols.py
+++ b/extract_symbols.py
@@ -2,7 +2,7 @@ import sys
 
 syscalls = {
 	'open_file': None,
-	'read_sectors': None,
+	'modify_sectors': None,
 	'draw_rect': None,
 }
 
diff --git a/ponydos.asm b/ponydos.asm
index 1a99f82..d008b44 100644
--- a/ponydos.asm
+++ b/ponydos.asm
@@ -11,7 +11,6 @@ org 0x7c00
 COLUMNS equ 80
 ROWS equ 25
 
-DIRENTS equ 0x2000
 DIRENT_SIZE equ 32
 FILE_MAX_SIZE equ 128
 
@@ -65,7 +64,8 @@ load_shell:
 	mov si, shell_name
 	call 0:open_file
 	xor bx, bx
-	call 0:read_sectors
+	xor di, di ; read
+	call 0:modify_sectors
 	; TODO: error management? Surely this works...
 
 	xor ax, ax ; WM_INITIALIZE
@@ -231,11 +231,11 @@ flip_mouse_cursor:
 ;;  bl = drive number
 ;  cx = number of sectors to read (must be at least 1)
 ;  es:bx = output buffer
+;  di = 0x0100 for write, 0x0000 for read
 ; [Far calls only]
-read_sectors:
+modify_sectors:
 	pusha
 
-	xor di, di
 	.loop:
 		call modify_sector
 		inc ax
@@ -299,10 +299,10 @@ shell_name db 'shell.bin', 0
 ; out:
 ;  ax = LBA of first sector, 0 if no space left
 ;  cx = length in sectors
+;  di = dirent address (in GLOBAL_DIRENTS)
 ; [Far calls only]
 open_file:
 	push si
-	push di
 	push bx
 	push es
 
@@ -319,7 +319,7 @@ open_file:
 	mov es, ax
 	;mov ax, 1
 	mov al, 1
-	mov bx, DIRENTS
+	mov bx, GLOBAL_DIRENTS
 	xor di, di
 	call modify_sector
 
@@ -329,48 +329,46 @@ open_file:
 		cmp word [es:di], 0
 		je .create_file
 
+		pusha
 		inc di
 		inc di
 
-		pusha
 		repe cmpsb
 		popa
 		je .success
 
 		add ax, FILE_MAX_SIZE
-		add di, DIRENT_SIZE - 2
-		cmp di, DIRENTS + 0x200
+		add di, DIRENT_SIZE
+		cmp di, GLOBAL_DIRENTS + 0x200
 		jl .loop
 
 	.error:
 	xor ax, ax
-	; Return with mangled cx
+	; Return with mangled cx, di
 	.success:
-	mov cx, [es:di - 2]
+	mov cx, [es:di]
 	.return:
 	pop es
 	pop bx
-	pop di
 	pop si
 	retf
 
 	.create_file:
 		; TODO: zero out the sector for this file?
 		inc word [es:di]
+
+		pusha
 		inc di
 		inc di
 		rep movsb
-		
-		push ax
+
 		mov ax, 1
-		;mov bx, DIRENTS
+		;mov bx, GLOBAL_DIRENTS
 		mov di, 0x0100 ; write
 		call modify_sector
-		pop ax
-		
-		;mov cx, 1
-		mov cl, 1
-		jmp .return
+		popa
+
+		jmp .success
 
 ; ------------------------------------------------------------------
 ; Mouse callback
diff --git a/ponydos_static.inc b/ponydos_static.inc
index d9005c9..1ec8106 100644
--- a/ponydos_static.inc
+++ b/ponydos_static.inc
@@ -1,6 +1,7 @@
 PONYDOS_SEG equ 0
 
 GLOBAL_WALLPAPER equ 0x500
+GLOBAL_DIRENTS equ 0x2000
 
 WM_INITIALIZE equ 0
 WM_PAINT equ 1
diff --git a/shell.asm b/shell.asm
index 3430946..5387601 100644
--- a/shell.asm
+++ b/shell.asm
@@ -49,7 +49,8 @@ initialize:
 	mov bp, PONYDOS_SEG
 	mov es, bp
 	mov bx, GLOBAL_WALLPAPER
-	call PONYDOS_SEG:SYS_READ_SECTORS
+	xor di, di ; read
+	call PONYDOS_SEG:SYS_MODIFY_SECTORS
 
 	; Put window 1 in the window chain
 	mov ax, cs