From 3349ec20ae5e1c5c628133c456ca6d424e69e0a6 Mon Sep 17 00:00:00 2001
From: d0p1 <contact@d0p1.eu>
Date: Mon, 2 Sep 2024 15:12:19 +0200
Subject: [PATCH] feat(boot): load kernel from StupidFS

---
 boot/loader/loader.asm |  10 +++
 boot/loader/stpdfs.inc | 164 +++++++++++++++++++++++++++++++++++------
 2 files changed, 152 insertions(+), 22 deletions(-)

diff --git a/boot/loader/loader.asm b/boot/loader/loader.asm
index 39a92e6..363f31c 100644
--- a/boot/loader/loader.asm
+++ b/boot/loader/loader.asm
@@ -84,7 +84,17 @@ _start:
 
 	mov si, szKernelStpdfsFile
 	call stpdfs_search
+	jc .error_not_found
 
+	call stpdfs_read_inode
+
+	mov ebx, dword [inode_cache + Inode.size]
+	mov [uKernelSize], ebx
+
+	mov ax, KERNEL_PRELOAD/0x10
+	mov es, ax
+	xor bx, bx
+	call stpdfs_copy_data
 
 	jmp .skip_fat
 
diff --git a/boot/loader/stpdfs.inc b/boot/loader/stpdfs.inc
index feacb75..f5d722b 100644
--- a/boot/loader/stpdfs.inc
+++ b/boot/loader/stpdfs.inc
@@ -1,6 +1,9 @@
-STPDFS_NAME_MAX = 28
+	;; File: stpdfs.inc
 
-	;; Struct: inode
+STPDFS_BLOCK_SIZE = 512
+STPDFS_NAME_MAX   = 28
+
+	;; Struct: Inode
 struc Inode {
 	.inode   dw ?
 	.nlink   dw ?
@@ -14,16 +17,19 @@ struc Inode {
 }
 DEFN Inode
 
-	;; Struct: dirent
-struc dirent {
+STPDFS_INODE_PER_BLOCK equ STPDFS_BLOCK_SIZE / sizeof.Inode
+
+	;; Struct: DirEntry
+struc DirEntry {
 	.inum dd ?
 	.name db STPDFS_NAME_MAX dup(?)
 }
-DEFN dirent
+DEFN DirEntry
 
 	;; Function: stpdfs_load_rootdir
 	;;
 	;; Out:
+	;;    
 stpdfs_load_rootdir:
 	; read first inode
 	mov ax, DISK_BUFFER/0x10
@@ -44,10 +50,48 @@ stpdfs_load_rootdir:
 
 	mov ax, DISK_BUFFER/0x10
 	mov es, ax
-
+	xor bx, bx
 	call stpdfs_copy_data
 
-	xchg bx, bx
+	ret
+
+	;; Function: stpdfs_read_inode
+	;; 
+	;; copy selected inode from file system to `inode_cache` 
+	;;
+	;; In:
+	;;    EAX - inum
+	;;
+stpdfs_read_inode:
+	; get block where inode is located
+	xor edx, edx
+	mov ecx, STPDFS_INODE_PER_BLOCK
+	div ecx
+	add eax, 2
+
+	; read block
+	push edx
+	push eax
+	mov ax, DISK_BUFFER/0x10
+	mov es, ax
+	pop eax
+	mov cx, 1
+	xor bx, bx
+	call disk_read_sectors
+	pop edx
+
+	; copy to inode cache
+	mov eax, edx
+	mov cl, sizeof.Inode
+	mul cl
+	movzx esi, ax
+	add esi, DISK_BUFFER
+
+	xor ax, ax
+	mov es, ax
+	mov ecx, sizeof.Inode
+	mov edi, inode_cache
+	rep movsb
 
 	ret
 
@@ -56,47 +100,123 @@ stpdfs_load_rootdir:
 	;; In:
 	;;    SI - filename
 	;;
+	;; Out:
+	;;    EAX - kernel inode
 stpdfs_search:
 	clc	; clear carry flag
+	
+	xor ax, ax
+	mov es, ax
 
+	xor ecx, ecx
+.search_loop:
+	cmp ecx, dword [inode_cache + Inode.size]
+	jge .search_end
 
+	push ecx
+
+	; check if inum != 0
+	mov eax, DISK_BUFFER
+	add eax, ecx
+	mov edx, [eax]
+
+	or edx, edx
+	jz .search_next
+
+	; compare filename
+	mov edi, eax
+	add edi, 4
+
+	push si
+.strcmp:
+	mov al, [si]
+	cmpsb
+	jne .strcmp_not_equal
+	or al, al
+	jz .kernel_found
+	jmp .strcmp
+.strcmp_not_equal:
+	pop si
+.search_next:
+	pop ecx
+	add ecx, sizeof.DirEntry
+	jmp .search_loop
+.search_end:
+	stc
+	ret
+.kernel_found:
+	pop si
+	pop ecx
+
+	mov eax, edx
+
+	clc
 	ret
 
 	;; Function: stpdfs_copy_data
 	;;
 	;; In:
-	;;	ES  - Buffer
+	;;	ES:BX - buffer
+	;;
 stpdfs_copy_data:
 	xor edx, edx
-	mov bx, es
 	movzx ebx, bx
-@@:
-	mov ax, es
-	movzx ecx, ax
-	sub ecx, ebx
-	cmp ecx, dword [inode_cache + Inode.size]
-	jg .all_read
 
+	;; read direct
+@@:
+	cmp ebx, dword [inode_cache + Inode.size]
+	jg .all_read
 	mov eax, edx
 	shl eax, 2
-	add eax, dword [inode_cache + Inode.zones]
+	add eax, inode_cache + Inode.zones
+	mov eax, [eax]
 
 	push edx
 	push ebx
 	mov cx, 1
-	xor bx, bx
 	call disk_read_sectors
 	pop ebx
 	pop edx
 
-	mov ax, es
-	add ax, 512
-	mov es, ax
+	add ebx, STPDFS_BLOCK_SIZE
 	inc edx
-	cmp edx, 8
-	jbe @b
+	cmp edx, 7
+	jb @b
 
 .indirect_read:
+	push ebx
+	mov ax, es
+	push ax
 
+	mov ax, DISK_BUFFER/0x10
+	mov es, ax
+	
+	mov eax, dword [inode_cache + Inode.zones + 28]
+	mov cx, 1
+	xor bx, bx
+	call disk_read_sectors
+
+	pop ax
+	mov es, ax
+
+	pop ebx
+	xor edx, edx
+@@:
+	cmp ebx, dword [inode_cache + Inode.size]
+	jg .all_read
+	mov eax, edx
+	shl eax, 2
+	add eax, DISK_BUFFER
+	mov eax, [eax]
+
+	mov cx, 1
+	push edx
+	call disk_read_sectors
+	pop edx
+
+	add ebx, STPDFS_BLOCK_SIZE
+	inc edx
+	cmp edx, 128
+	jbe @b
 .all_read:
 	ret