adding reference impementation for reading files from fat
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2c44bea9b1
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da1a2345a9
3 changed files with 167 additions and 10 deletions
57
build.zig
57
build.zig
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@ -18,16 +18,40 @@ pub fn build(b: *std.Build) void {
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var floppy = createFloppy(b, "main_floppy.img");
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var floppy = createFloppy(b, "main_floppy.img");
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floppy.run = formatFloppyFat12(b, floppy);
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floppy.run = formatFloppyFat12(b, floppy);
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var installToFloppy = installImgToFloppy(b, floppy, initramfs, &.{
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NamedFile{ .file = .{ .runFile = kernel }, .name = "::kernel.bin" },
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NamedFile{ .file = .{ .simpleFile = b.path("src/reference_implementations/test.txt") }, .name = "::test.txt" },
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});
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const img_install = b.addInstallBinFile(floppy.obj, "main_floppy.img");
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const img_install = b.addInstallBinFile(floppy.obj, "main_floppy.img");
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img_install.step.dependOn(&installImgToFloppy(b, floppy, initramfs, kernel).step);
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img_install.step.dependOn(&installToFloppy);
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b.getInstallStep().dependOn(&img_install.step);
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b.getInstallStep().dependOn(&img_install.step);
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const target = b.standardTargetOptions(.{});
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const fat_reference_mod = b.createModule(.{
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.root_source_file = b.path("src/reference_implementations/fat.zig"),
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.target = target,
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.link_libc = true,
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});
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const run = b.addSystemCommand(&.{ "qemu-system-i386", "-fda" });
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const run = b.addSystemCommand(&.{ "qemu-system-i386", "-fda" });
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run.addFileArg(floppy.obj);
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run.addFileArg(floppy.obj);
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const run_step = b.step("run", "run the os in qemu");
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const run_step = b.step("run", "run the os in qemu");
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run_step.dependOn(&run.step);
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run_step.dependOn(&run.step);
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const fat_reference = b.addExecutable(.{
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.root_module = fat_reference_mod,
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.name = "fat_reference_implementation",
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.use_lld = false,
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.use_llvm = false,
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});
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const fat_install = b.addInstallArtifact(fat_reference, .{});
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const build_references = b.step("references", "build the reference implementations");
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build_references.dependOn(&fat_install.step);
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}
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}
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const AddNasmFilesOptions = struct {
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const AddNasmFilesOptions = struct {
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@ -43,6 +67,11 @@ const NasmFile = struct {
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const Floppydisk = NasmFile;
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const Floppydisk = NasmFile;
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const NamedFile = struct {
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file: union(enum) { runFile: NasmFile, simpleFile: std.Build.LazyPath },
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name: []const u8,
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};
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fn createFloppy(b: *std.Build, name: []const u8) Floppydisk {
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fn createFloppy(b: *std.Build, name: []const u8) Floppydisk {
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const dd = b.addSystemCommand(&.{ "dd", "if=/dev/zero" });
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const dd = b.addSystemCommand(&.{ "dd", "if=/dev/zero" });
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const Floppy = dd.addPrefixedOutputFileArg("of=", name);
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const Floppy = dd.addPrefixedOutputFileArg("of=", name);
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@ -63,7 +92,7 @@ fn formatFloppyFat12(b: *std.Build, floppy: Floppydisk) *std.Build.Step.Run {
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return mkfs;
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return mkfs;
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}
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}
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fn installImgToFloppy(b: *std.Build, floppy: Floppydisk, bootloader: NasmFile, kernel: NasmFile) *std.Build.Step.Run {
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fn installImgToFloppy(b: *std.Build, floppy: Floppydisk, bootloader: NasmFile, additional_files: []const NamedFile) std.Build.Step {
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const dd = b.addSystemCommand(&.{"dd"});
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const dd = b.addSystemCommand(&.{"dd"});
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dd.addPrefixedFileArg("if=", bootloader.obj);
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dd.addPrefixedFileArg("if=", bootloader.obj);
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dd.addPrefixedFileArg("of=", floppy.obj);
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dd.addPrefixedFileArg("of=", floppy.obj);
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@ -71,14 +100,22 @@ fn installImgToFloppy(b: *std.Build, floppy: Floppydisk, bootloader: NasmFile, k
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dd.step.dependOn(&floppy.run.step);
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dd.step.dependOn(&floppy.run.step);
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dd.step.dependOn(&bootloader.run.step);
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dd.step.dependOn(&bootloader.run.step);
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const mcopy = b.addSystemCommand(&.{"mcopy"});
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var mcopy_step = std.Build.Step.init(.{ .name = "mcopy", .owner = b, .id = .custom });
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mcopy.addPrefixedFileArg("-i", floppy.obj);
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mcopy_step.dependOn(&dd.step);
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mcopy.addFileArg(kernel.obj);
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for (additional_files) |f| {
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mcopy.addArg("::kernel.bin");
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const mcopy = b.addSystemCommand(&.{"mcopy"});
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mcopy.step.dependOn(&dd.step);
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mcopy.addPrefixedFileArg("-i", floppy.obj);
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mcopy.step.dependOn(&kernel.run.step);
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switch (f.file) {
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.runFile => |file| {
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return mcopy;
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mcopy.addFileArg(file.obj);
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mcopy_step.dependOn(&file.run.step);
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},
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.simpleFile => |file| mcopy.addFileArg(file),
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}
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mcopy.addArg(f.name);
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mcopy_step.dependOn(&mcopy.step);
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}
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return mcopy_step;
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}
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}
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// adapted from https://codeberg.org/raddari/zig-nasm-lib.git
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// adapted from https://codeberg.org/raddari/zig-nasm-lib.git
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117
src/reference_implementations/fat.zig
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117
src/reference_implementations/fat.zig
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@ -0,0 +1,117 @@
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const std = @import("std");
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const Errors = error{ InvalidSyntax, ReadSectors, FileNotFound };
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var buffer: [1024]u8 = undefined;
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var g_Fat: []u8 = undefined;
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const BootSector = extern struct {
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BootJumpInstruction: [3]u8 align(1),
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OemIdentifier: [8]u8 align(1),
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BytesPerSector: u16 align(1),
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SectorsPerCluster: u8 align(1),
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ReservedSectors: u16 align(1),
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FatCount: u8 align(1),
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DirEntryCount: u16 align(1),
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TotalSectors: u16 align(1),
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MediaDescriptorType: u8 align(1),
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SectorsPerFat: u16 align(1),
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SectorsPerTrack: u16 align(1),
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Heads: u16 align(1),
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HiddenSectors: u32 align(1),
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LargeSectorCount: u32 align(1),
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// ebr
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DriveNumber: u8 align(1),
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_Reserved: u8 align(1),
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Signature: u8 align(1),
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VolumeId: u32 align(1),
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VolumeLaber: [11]u8 align(1),
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SystemId: [8]u8 align(1),
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};
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var g_BootSector: BootSector = undefined;
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const DirectoryEntry = extern struct {
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Name: [11]u8 align(1),
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Attributes: u8 align(1),
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_Reserved: u8 align(1),
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CreatedTimeTenths: u8 align(1),
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CreatedTime: u16 align(1),
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CreatedDate: u16 align(1),
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AccessedDate: u16 align(1),
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FirstClusterHigh: u16 align(1),
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ModifiedTime: u16 align(1),
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ModifiedDate: u16 align(1),
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FirstClusterLow: u16 align(1),
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Size: u32 align(1),
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};
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var g_RootDirectory: []DirectoryEntry = undefined;
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fn readStruct(reader: *std.fs.File.Reader, T: type) !T {
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var ret: [@sizeOf(T)]u8 = undefined;
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_ = try reader.*.read(&ret);
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return @bitCast(ret);
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}
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fn readBootSector(disk: *std.fs.File) !void {
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var reader = disk.*.reader(&buffer);
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g_BootSector = try readStruct(&reader, BootSector);
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}
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fn readSectors(disk: *std.fs.File, lba: u32, count: u32, bufferOut: *[]anyopaque) !void {
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const dest: []u8 = try std.heap.smp_allocator.alloc(u8, g_BootSector.BytesPerSector * count);
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defer std.heap.smp_allocator.free(dest);
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var stream = disk.readerStreaming(&buffer);
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try stream.seekTo(lba * g_BootSector.BytesPerSector);
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if (try stream.readStreaming(dest) != g_BootSector.BytesPerSector * count) return Errors.ReadSectors;
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@memcpy(@as(*[]u8, @ptrCast(bufferOut)).*, dest);
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}
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fn readFat(disk: *std.fs.File) !void {
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g_Fat = try std.heap.smp_allocator.alloc(u8, g_BootSector.SectorsPerFat * g_BootSector.BytesPerSector);
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errdefer std.heap.smp_allocator.free(g_Fat);
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try readSectors(disk, g_BootSector.ReservedSectors, g_BootSector.SectorsPerFat, &g_Fat);
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}
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fn readRootDirectory(disk: std.fs.File) !void {
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const lba: u32 = g_BootSector.ReservedSectors + g_BootSector.SectorsPerFat + g_BootSector.FatCount;
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const size: u32 = @sizeOf(DirectoryEntry) * g_BootSector.DirEntryCount;
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const sectors: u32 = (size / g_BootSector.BytesPerSector);
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if (@rem(size, g_BootSector.BytesPerSector > 0))
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sectors += 1;
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g_RootDirectory = try std.heap.smp_allocator.alloc(DirectoryEntry, sectors * g_BootSector.BytesPerSector);
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errdefer std.heap.smp_allocator.free(g_RootDirectory);
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try readSectors(disk, lba, sectors, &g_RootDirectory);
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}
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fn findFile(name: []const u8) !*DirectoryEntry {
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for (g_RootDirectory, 0..) |Entry, i|
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if (std.mem.eql(u8, Entry.Name, name))
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return &g_RootDirectory[i];
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return Errors.FileNotFound;
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}
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pub fn main() !void {
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if (std.os.argv.len < 3) {
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std.log.err("syntax: {s} <disk image> <file name>", .{std.os.argv[0]});
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return Errors.InvalidSyntax;
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}
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var disk = try std.fs.cwd().openFileZ(std.os.argv[1], .{ .mode = .read_only });
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_ = &disk;
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try readBootSector(&disk);
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try readFat(&disk);
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defer std.heap.smp_allocator.free(g_Fat);
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try readRootDirectory(disk);
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defer std.heap.smp_allocator.free(g_RootDirectory);
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const fileEntry = try findFile(std.os.argv[2]);
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_ = fileEntry;
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}
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3
src/reference_implementations/test.txt
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3
src/reference_implementations/test.txt
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@ -0,0 +1,3 @@
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testing file
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aabaacaadaaeaafaagaahaaiaajaakaalaamaanaaoaapaaqaaraasaataauaavaawaaxaayaaz
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tstngfl
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