From babf3897f4d3dda277c3de3ad2acf11c9f0d2a09 Mon Sep 17 00:00:00 2001
From: Alexander Myltsev <a.myltsev@gmail.com>
Date: Tue, 13 Dec 2022 00:50:28 +0300
Subject: [PATCH] Add fs.c.

---
 Makefile      |  3 ++-
 drivers/ata.h |  3 +--
 fs/fs.c       | 39 +++++++++++++++++++++++++++++++++++++++
 fs/fs.h       |  3 ++-
 kernel.c      | 10 +++++++---
 string.c      | 12 ++++++++++++
 string.h      |  1 +
 7 files changed, 64 insertions(+), 7 deletions(-)
 create mode 100644 fs/fs.c

diff --git a/Makefile b/Makefile
index 351c481..d0e184e 100644
--- a/Makefile
+++ b/Makefile
@@ -59,7 +59,8 @@ image.bin: mbr.bin fs.img
 	cat $^ >$@
 
 kernel.bin: kernel.o console.o drivers/vga.o drivers/keyboard.o \
-	string.o drivers/ata.o cpu/vectors.o cpu/idt.o cpu/gdt.o drivers/uart.o
+	string.o drivers/ata.o cpu/vectors.o cpu/idt.o cpu/gdt.o drivers/uart.o \
+	fs/fs.o
 	$(LD) $(LDFLAGS) -o $@ -Ttext 0x1000 $^
 
 %.o: %.c
diff --git a/drivers/ata.h b/drivers/ata.h
index 3d5b3d6..67aea2f 100644
--- a/drivers/ata.h
+++ b/drivers/ata.h
@@ -1,5 +1,4 @@
 #pragma once
 #include <stdint.h>
 
-void read_sectors_ATA_PIO(uint32_t target_address, uint32_t LBA, uint8_t sector_count);
-void write_sectors_ATA_PIO(uint32_t LBA, uint8_t sector_count, uint32_t* bytes);
+void read_sectors_ATA_PIO(void* target_address, uint32_t LBA, uint8_t sector_count);
diff --git a/fs/fs.c b/fs/fs.c
new file mode 100644
index 0000000..6a5c74a
--- /dev/null
+++ b/fs/fs.c
@@ -0,0 +1,39 @@
+#include "fs.h"
+#include "../string.h"
+#include "../drivers/ata.h"
+
+enum {
+    fs_start = 1, // sector where the FS starts
+};
+
+int stat(const char* name, struct stat *buf) {
+    struct dir dir;
+    read_sectors_ATA_PIO(&dir, fs_start, 1);
+    for (int i = 0; i < ents_in_dir; ++i) {
+        struct dirent *e = &dir.entries[i];
+        if (!strncmp(e->name, name, sizeof(e->name))) {
+            buf->size = e->size_bytes;
+            buf->reserved[0] = e->offset_sectors;
+            return 0;
+        }
+    }
+    return -1;
+}
+
+/* Find file by name and read it into buffer with size bufsize.
+ * At most (bufsize & -512) bytes will be read.
+ * Return number of bytes read or -1 on failure. */
+int read_file(const char* name, void* buf, uint32_t bufsize) {
+    struct stat statbuf;
+    if (stat(name, &statbuf) != 0) {
+        return -1;
+    }
+    uint32_t sector = fs_start + statbuf.reserved[0];
+    while (bufsize >= sector_size) {
+        read_sectors_ATA_PIO(buf, sector, 1);
+        sector++;
+        bufsize -= sector_size;
+        buf += sector_size;
+    }
+    return 0;
+}
diff --git a/fs/fs.h b/fs/fs.h
index 8de61a3..67f01a2 100644
--- a/fs/fs.h
+++ b/fs/fs.h
@@ -21,6 +21,7 @@ size is in bytes, name is 0-terminated.
 
 enum {
 	sector_size = 512,
+	ents_in_dir = 15,
 };
 
 struct dirent {
@@ -32,7 +33,7 @@ struct dirent {
 
 struct dir {
 	char reserved[32];
-	struct dirent entries[15];
+	struct dirent entries[ents_in_dir];
 };
 
 struct stat {
diff --git a/kernel.c b/kernel.c
index 430c8d5..a7b3ec2 100644
--- a/kernel.c
+++ b/kernel.c
@@ -8,6 +8,7 @@ asm(".asciz \"kernel start\"");
 #include "drivers/ata.h"
 #include "drivers/misc.h"
 #include "drivers/uart.h"
+#include "fs/fs.h"
 
 void _start() {
     load_gdt();
@@ -15,13 +16,16 @@ void _start() {
     uartinit();
     load_idt();
     sti();
-    char buf[512];
+    char buf[4096 + 512];
 
     vga_clear_screen();
     printk("YABLOKO\n");
 
-    read_sectors_ATA_PIO((uint32_t)buf, 10, 1);
-    printk(buf);
+    if (read_file("kernel.bin", buf, sizeof(buf)) == 0) {
+        printk(buf + 4096);
+    } else {
+        printk("failed to read file\n");
+    }
 
     while (1) {
         asm("hlt");
diff --git a/string.c b/string.c
index bb71bff..99e1171 100644
--- a/string.c
+++ b/string.c
@@ -14,3 +14,15 @@ void kmemmove(char* dst, char* src, size_t size) {
 		}
 	}
 }
+
+int strncmp(const char* s1, const char* s2, size_t size) {
+    while (size && *s1 && *s2 && *s1 == *s2) {
+        size--;
+        s1++;
+        s2++;
+    }
+    if (!size) {
+        return 0;
+    }
+    return (unsigned char)(*s1) - (unsigned char)(*s2);
+}
diff --git a/string.h b/string.h
index 9d8b0de..584f7d7 100644
--- a/string.h
+++ b/string.h
@@ -3,3 +3,4 @@
 typedef unsigned size_t;
 
 void kmemmove(char* dst, char* src, size_t size);
+int strncmp(const char* s1, const char* s2, size_t size);