exfat: the engine read path (S4 step 2)
mount + resolve + list + read over a BlockDevice, host-tested against a RAM-backed image the tests build with formatExfat. mount reads the VBR, loads the geometry, and scans the root for the Allocation Bitmap (0x81) and Up-case Table (0x82); the up-case prefix is decompressed (0xFFFF identity runs) into a bounded table so names fold correctly. A directory is read as consecutive 32-byte entries via readChain, so a File/Stream/Name SET that straddles a sector or cluster boundary assembles cleanly; each set's checksum is validated before it counts as a file. A stream's no_fat_chain flag picks contiguous-arithmetic vs FAT-follow cluster walking. reads honor valid_data_length (allocated- but-unwritten tail reads as zero) and clamp data_length to the vfs u32 offset surface. Tests cover mount + up-case fold, listing (skipping the metadata entries), case-insensitive resolve, and reads across a cluster boundary on both a contiguous and a FAT-fragmented file. Wired via engine.zig (which imports on-disk.zig) into the host-test aggregate. 12/12, bounds green. Write path is step 3.
This commit is contained in:
Daniel Samson
@@ -422,9 +422,10 @@ pub fn build(b: *std.Build) void {
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"system/boot-handoff.zig",
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"system/abi.zig",
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"system/initial-ramdisk.zig", // v2 path-named entries: find/basename/magic
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// The exFAT engine's pure on-disk layer (S4), std-only, before its package
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// exists — moves into the `exfat` package's own test step once that lands.
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"system/services/exfat/on-disk.zig",
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// The exFAT engine (S4), std-only, before its package exists — the
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// engine imports on-disk.zig, so this one entry runs both files' tests.
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// Moves into the `exfat` package's own test step once that lands (step 4).
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"system/services/exfat/engine.zig",
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}) |root| {
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const mod_tests = b.addTest(.{
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.root_module = b.createModule(.{
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@@ -0,0 +1,730 @@
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//! The exFAT filesystem engine: mount a block device, walk the allocation
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//! structures and directory entry sets, and (this step) resolve, list, and read.
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//! Pure logic over a `BlockDevice` interface — no IPC — host-testable against a
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//! RAM-backed image (the tests at the bottom build one with `formatExfat`). The
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//! exfat.zig server wraps a real `.block` device and serves this over the VFS
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//! protocol through the shared filesystem harness, exactly as fat.zig does.
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//!
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//! Three things differ from FAT and shape this file. A file is a directory-entry
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//! SET — a File entry (0x85), a Stream Extension (0xC0), then File Name entries
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//! (0xC1) — read as consecutive 32-byte entries that may cross sector and cluster
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//! boundaries. A stream's `no_fat_chain` flag says its clusters are contiguous
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//! (walk by arithmetic) or fragmented (follow the 32-bit FAT). And names are
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//! matched case-folded through the volume's own on-disk up-case table, a bounded
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//! prefix of which is loaded at mount. Allocation authority (the bitmap) is the
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//! write path's concern (step 3); reads never touch it.
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//!
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//! Everything works in 512-byte sectors; a cluster is N sectors.
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const std = @import("std");
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const on_disk = @import("on-disk.zig");
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const sector_size = 512;
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const name_units_per_entry = on_disk.name_units_per_entry; // 15
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/// bound: UTF-16 units of a file name (the longest name a listing/resolve handles)
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/// decided-by: external
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/// protects: the on-stack name buffers and the Listing name_buffer
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/// at-limit: truncate - the exFAT format caps a name at 255 units, so a longer
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/// name is impossible on a valid volume; a corrupt over-long name is cut and the
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/// set's checksum mismatch (checked on read) flags it
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/// observed-by: a set-checksum rejection in scanDirectory
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const name_maximum = 255;
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/// bound: code points whose case-fold the engine loads from the up-case table
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/// decided-by: ours
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/// protects: the in-memory `upcase` table
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/// at-limit: truncate - code points at or above this fold to themselves, so two
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/// names differing only in case ABOVE this point compare as distinct (danos
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/// names are ASCII, far below it)
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/// observed-by: a case-only-different high-plane name resolving as not-found
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const upcase_fold_limit = 256;
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/// bound: 32-byte entries one directory scan will read before giving up
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/// decided-by: ours
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/// protects: scanDirectory / mount against a directory with no end marker or a
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/// cyclic cluster chain (a corrupt medium)
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/// at-limit: truncate - entries beyond are not listed or resolved; a real
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/// directory is far smaller, so hitting this means corruption
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/// observed-by: an on-disk file absent from a listing under a huge directory
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const directory_entry_scan_maximum = 65536;
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/// The most sectors one multi-sector transfer moves (the DMA bounce the exfat
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/// server sizes to). The engine's read path works a sector at a time, so this only
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/// bounds the server's buffer; kept for parity with the fat engine.
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/// bound: sectors in one coalesced device transfer
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/// decided-by: ours
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/// protects: the exfat server's DMA bounce buffer (max_transfer_sectors * 512)
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/// at-limit: truncate - a longer run is split into several transfers, no data lost
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/// observed-by: more device commands than the ideal, never a wrong byte
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pub const max_transfer_sectors = 8;
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const block_cache_lines = 16;
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/// A block device the engine reads and writes in fixed-size blocks (identical to
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/// the fat engine's — the shared harness is generic over whichever engine wraps a
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/// real `.block` driver or, in tests, a RAM buffer).
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pub const BlockDevice = struct {
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context: *anyopaque,
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block_size: u32,
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block_count: u64,
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readBlocksFn: *const fn (context: *anyopaque, lba: u64, count: u32, buffer: []u8) bool,
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writeBlocksFn: *const fn (context: *anyopaque, lba: u64, count: u32, buffer: []const u8) bool,
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pub fn readBlocks(self: BlockDevice, lba: u64, count: u32, buffer: []u8) bool {
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return self.readBlocksFn(self.context, lba, count, buffer);
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}
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pub fn writeBlocks(self: BlockDevice, lba: u64, count: u32, buffer: []const u8) bool {
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return self.writeBlocksFn(self.context, lba, count, buffer);
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}
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pub fn readBlock(self: BlockDevice, lba: u64, buffer: []u8) bool {
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return self.readBlocksFn(self.context, lba, 1, buffer);
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}
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pub fn writeBlock(self: BlockDevice, lba: u64, buffer: []const u8) bool {
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return self.writeBlocksFn(self.context, lba, 1, buffer);
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}
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};
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/// A resolved filesystem object and where its directory-entry set lives, so writes
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/// (step 3) can rewrite the Stream entry's sizes/first-cluster and recompute the
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/// set checksum.
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pub const Node = struct {
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first_cluster: u32,
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size: u32, // data_length, clamped to the vfs u32 offset surface
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is_directory: bool,
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no_fat_chain: bool = false,
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valid_data_length: u32 = 0, // bytes actually written; [valid, size) read as zero
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mtime: u64 = 0,
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// The set's home: its parent directory's chain and the File entry's linear
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// 32-byte-entry index within it, plus how many secondary entries follow.
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parent_first_cluster: u32 = 0,
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parent_no_fat_chain: bool = false,
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entry_index: u64 = 0,
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secondary_count: u8 = 0,
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has_entry: bool = false,
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};
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pub const Listing = struct {
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name_buffer: [name_maximum]u8 = undefined,
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name_len: usize = 0,
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is_directory: bool = false,
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size: u32 = 0,
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mtime: u64 = 0,
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};
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const CacheLine = struct {
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lba: u64 = 0,
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valid: bool = false,
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data: [sector_size]u8 = undefined,
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};
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pub const FileSystem = struct {
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device: BlockDevice,
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geometry: on_disk.Geometry,
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base_lba: u64 = 0, // the volume manager confines the channel volume-relative
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sector: [sector_size]u8 = undefined,
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cache: [block_cache_lines]CacheLine = [_]CacheLine{.{}} ** block_cache_lines,
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cache_cursor: u32 = 0,
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// The case-fold table, a bounded prefix loaded at mount (unit -> uppercase).
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upcase: [upcase_fold_limit]u16 = undefined,
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upcase_len: usize = 0,
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// The allocation bitmap's location, for the write path (step 3).
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bitmap_first_cluster: u32 = 0,
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bitmap_length: u64 = 0, // bytes
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// Wall-clock (Unix epoch seconds) the server sets before a mutating op.
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current_time_epoch: u64 = 0,
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// --- single-sector write-through cache ----------------------------------
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fn cacheFind(self: *FileSystem, lba: u64) ?*CacheLine {
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for (&self.cache) |*line| if (line.valid and line.lba == lba) return line;
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return null;
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}
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fn cacheInstall(self: *FileSystem, lba: u64, data: []const u8) void {
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const line = self.cacheFind(lba) orelse blk: {
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const slot = &self.cache[self.cache_cursor];
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self.cache_cursor = (self.cache_cursor + 1) % block_cache_lines;
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slot.valid = true;
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slot.lba = lba;
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break :blk slot;
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};
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@memcpy(&line.data, data[0..sector_size]);
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}
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fn cacheInvalidateRange(self: *FileSystem, lba: u64, count: u32) void {
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for (&self.cache) |*line| {
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if (line.valid and line.lba >= lba and line.lba < lba + count) line.valid = false;
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}
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}
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fn blockRead(self: *FileSystem, lba: u64, buffer: []u8) bool {
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if (self.cacheFind(lba)) |line| {
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@memcpy(buffer[0..sector_size], &line.data);
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return true;
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}
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if (!self.device.readBlock(self.base_lba + lba, buffer)) return false;
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self.cacheInstall(lba, buffer);
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return true;
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}
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fn blockWrite(self: *FileSystem, lba: u64, buffer: []const u8) bool {
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if (!self.device.writeBlock(self.base_lba + lba, buffer)) return false;
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self.cacheInstall(lba, buffer);
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return true;
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}
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// --- cluster <-> sector, and the FAT ------------------------------------
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fn clusterBytes(self: *const FileSystem) u32 {
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return self.geometry.sectors_per_cluster * sector_size;
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}
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fn clusterSector(self: *const FileSystem, cluster: u32, sector_in_cluster: u32) u64 {
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return @as(u64, self.geometry.cluster_heap_offset_sectors) +
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@as(u64, cluster - 2) * self.geometry.sectors_per_cluster + sector_in_cluster;
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}
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fn validCluster(self: *const FileSystem, cluster: u32) bool {
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return cluster >= on_disk.first_data_cluster and cluster < self.geometry.cluster_count + on_disk.first_data_cluster;
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}
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/// Read the 32-bit FAT entry for `cluster` (exFAT's FAT is only consulted for a
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/// fragmented chain — a stream with `no_fat_chain` clear, or the metadata).
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fn readFatEntry(self: *FileSystem, cluster: u32) u32 {
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const byte = @as(u64, self.geometry.fat_offset_sectors) * sector_size + @as(u64, cluster) * 4;
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const lba = byte / sector_size;
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const within: usize = @intCast(byte % sector_size);
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if (!self.blockRead(lba, &self.sector)) return on_disk.end_of_chain;
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return std.mem.readInt(u32, self.sector[within..][0..4], .little);
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}
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fn isEndOfChain(_: *const FileSystem, value: u32) bool {
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return value >= 0xFFFFFFF8; // EOC (0xFFFFFFFF) or bad (0xFFFFFFF7) and up
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}
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/// The `index`-th cluster of a chain: contiguous arithmetic when `no_fat_chain`,
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/// else a FAT walk. Null past the end or off a corrupt/out-of-range link.
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fn clusterOfChain(self: *FileSystem, first: u32, no_fat_chain: bool, index: u32) ?u32 {
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if (!self.validCluster(first)) return null;
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if (no_fat_chain) {
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const cluster = first + index;
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return if (self.validCluster(cluster)) cluster else null;
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}
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var cluster = first;
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var steps = index;
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while (steps > 0) : (steps -= 1) {
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const next = self.readFatEntry(cluster);
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if (self.isEndOfChain(next) or !self.validCluster(next)) return null;
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cluster = next;
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}
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return cluster;
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}
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/// Read up to `out.len` bytes of a cluster chain starting at `byte_offset`,
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/// a sector at a time. Returns bytes produced (short at the chain's end).
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fn readChain(self: *FileSystem, first: u32, no_fat_chain: bool, byte_offset: u64, out: []u8) usize {
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const cluster_bytes = self.clusterBytes();
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var produced: usize = 0;
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var position = byte_offset;
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while (produced < out.len) {
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const cluster = self.clusterOfChain(first, no_fat_chain, @intCast(position / cluster_bytes)) orelse break;
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const in_cluster: u32 = @intCast(position % cluster_bytes);
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const lba = self.clusterSector(cluster, in_cluster / sector_size);
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const in_sector = in_cluster % sector_size;
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if (!self.blockRead(lba, &self.sector)) break;
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const n = @min(out.len - produced, sector_size - in_sector);
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@memcpy(out[produced .. produced + n], self.sector[in_sector .. in_sector + n]);
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produced += n;
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position += n;
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}
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return produced;
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}
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/// Read the `index`-th 32-byte directory entry (an entry never straddles a
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/// sector: 512/32 divides evenly and entries are 32-aligned).
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fn entryAt(self: *FileSystem, dir_first: u32, dir_no_fat_chain: bool, index: u64, out: *[on_disk.entry_bytes]u8) bool {
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return self.readChain(dir_first, dir_no_fat_chain, index * on_disk.entry_bytes, out) == on_disk.entry_bytes;
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}
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// --- the up-case table --------------------------------------------------
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fn fold(self: *const FileSystem, unit: u16) u16 {
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return if (unit < self.upcase_len) self.upcase[unit] else unit;
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}
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/// Load a bounded prefix of the on-disk up-case table (unit -> uppercase),
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/// decompressing 0xFFFF identity runs. Any prefix entry the table does not
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/// reach folds to itself.
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fn loadUpcase(self: *FileSystem, first_cluster: u32, data_length: u64) void {
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var raw: [upcase_fold_limit * 2]u8 = undefined;
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const want: usize = @intCast(@min(data_length, @as(u64, raw.len)));
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const got = self.readChain(first_cluster, false, 0, raw[0..want]);
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var out_index: usize = 0;
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var in_index: usize = 0;
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while (out_index < upcase_fold_limit and in_index + 2 <= got) {
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const value = std.mem.readInt(u16, raw[in_index..][0..2], .little);
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in_index += 2;
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if (value == 0xFFFF and in_index + 2 <= got) {
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var run = std.mem.readInt(u16, raw[in_index..][0..2], .little);
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in_index += 2;
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while (run > 0 and out_index < upcase_fold_limit) : (run -= 1) {
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self.upcase[out_index] = @intCast(out_index);
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out_index += 1;
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}
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} else {
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self.upcase[out_index] = value;
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out_index += 1;
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}
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}
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while (out_index < upcase_fold_limit) : (out_index += 1) self.upcase[out_index] = @intCast(out_index);
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self.upcase_len = upcase_fold_limit;
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}
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// --- mount --------------------------------------------------------------
|
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/// Mount an exFAT volume: read the VBR, load the geometry, then scan the root
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/// directory for the Allocation Bitmap (0x81) and Up-case Table (0x82). Null
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/// unless it is a 512-byte-sector exFAT volume.
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pub fn mount(device: BlockDevice) ?FileSystem {
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var boot: [sector_size]u8 = undefined;
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if (!device.readBlock(0, &boot)) return null;
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const geometry = on_disk.geometryOf(&boot) orelse return null;
|
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if (geometry.bytes_per_sector != sector_size) return null; // danos handles 512-byte sectors
|
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|
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var fs = FileSystem{ .device = device, .geometry = geometry };
|
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// Identity fold until the table loads, so a volume with no up-case entry
|
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// still matches ASCII case-insensitively is NOT assumed — we only fold what
|
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// the table gives; unloaded means case-sensitive. loadUpcase fills it.
|
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fs.upcase_len = 0;
|
||||
|
||||
var index: u64 = 0;
|
||||
var found_upcase = false;
|
||||
while (index < directory_entry_scan_maximum) : (index += 1) {
|
||||
var raw: [on_disk.entry_bytes]u8 = undefined;
|
||||
if (!fs.entryAt(geometry.first_cluster_of_root, false, index, &raw)) break;
|
||||
switch (raw[0]) {
|
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on_disk.entry_type_end_of_directory => break,
|
||||
on_disk.entry_type_allocation_bitmap => {
|
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const entry = std.mem.bytesToValue(on_disk.AllocationBitmapEntry, &raw);
|
||||
if (fs.bitmap_first_cluster == 0) { // the first (active, flags bit0=0) bitmap
|
||||
fs.bitmap_first_cluster = entry.first_cluster;
|
||||
fs.bitmap_length = entry.data_length;
|
||||
}
|
||||
},
|
||||
on_disk.entry_type_upcase_table => {
|
||||
if (!found_upcase) {
|
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const entry = std.mem.bytesToValue(on_disk.UpcaseTableEntry, &raw);
|
||||
fs.loadUpcase(entry.first_cluster, entry.data_length);
|
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found_upcase = true;
|
||||
}
|
||||
},
|
||||
else => {},
|
||||
}
|
||||
}
|
||||
return fs;
|
||||
}
|
||||
|
||||
pub fn rootNode(self: *const FileSystem) Node {
|
||||
return .{
|
||||
.first_cluster = self.geometry.first_cluster_of_root,
|
||||
.size = 0,
|
||||
.is_directory = true,
|
||||
.no_fat_chain = false, // the root's chain is followed via the FAT
|
||||
.has_entry = false,
|
||||
};
|
||||
}
|
||||
|
||||
// --- directory scan (entry-set assembly) --------------------------------
|
||||
|
||||
fn nameMatches(self: *const FileSystem, display: []const u8, query: []const u8) bool {
|
||||
if (display.len != query.len) return false;
|
||||
for (display, query) |a, b| {
|
||||
if (self.fold(a) != self.fold(b)) return false;
|
||||
}
|
||||
return true;
|
||||
}
|
||||
|
||||
/// Assemble each File-entry SET in `dir` and hand it to `visit`. Stops when
|
||||
/// `visit` returns true, the directory ends, or the scan cap is hit.
|
||||
fn scanDirectory(
|
||||
self: *FileSystem,
|
||||
dir: Node,
|
||||
context: anytype,
|
||||
comptime visit: fn (@TypeOf(context), node: Node, name: []const u8) bool,
|
||||
) void {
|
||||
var index: u64 = 0;
|
||||
while (index < directory_entry_scan_maximum) {
|
||||
var raw: [on_disk.entry_bytes]u8 = undefined;
|
||||
if (!self.entryAt(dir.first_cluster, dir.no_fat_chain, index, &raw)) return;
|
||||
if (raw[0] == on_disk.entry_type_end_of_directory) return;
|
||||
if (raw[0] != on_disk.entry_type_file) {
|
||||
index += 1;
|
||||
continue;
|
||||
}
|
||||
const file = std.mem.bytesToValue(on_disk.FileEntry, &raw);
|
||||
|
||||
var stream_raw: [on_disk.entry_bytes]u8 = undefined;
|
||||
if (!self.entryAt(dir.first_cluster, dir.no_fat_chain, index + 1, &stream_raw)) return;
|
||||
if (stream_raw[0] != on_disk.entry_type_stream_extension) {
|
||||
index += 1;
|
||||
continue; // a File entry without its Stream — malformed, skip
|
||||
}
|
||||
const stream = std.mem.bytesToValue(on_disk.StreamExtensionEntry, &stream_raw);
|
||||
|
||||
// Reconstruct the name from the File Name entries, and validate the
|
||||
// whole set's checksum as we go (over File + Stream + Name bytes).
|
||||
var checksum_bytes: [on_disk.entry_bytes * (1 + 255)]u8 = undefined;
|
||||
@memcpy(checksum_bytes[0..on_disk.entry_bytes], &raw);
|
||||
@memcpy(checksum_bytes[on_disk.entry_bytes .. on_disk.entry_bytes * 2], &stream_raw);
|
||||
var set_bytes: usize = on_disk.entry_bytes * 2;
|
||||
|
||||
var name_buf: [name_maximum]u8 = undefined;
|
||||
var name_len: usize = 0;
|
||||
const name_entries = (@as(usize, stream.name_length) + name_units_per_entry - 1) / name_units_per_entry;
|
||||
var e: usize = 0;
|
||||
var malformed = false;
|
||||
while (e < name_entries) : (e += 1) {
|
||||
var fn_raw: [on_disk.entry_bytes]u8 = undefined;
|
||||
if (!self.entryAt(dir.first_cluster, dir.no_fat_chain, index + 2 + e, &fn_raw)) return;
|
||||
if (fn_raw[0] != on_disk.entry_type_file_name) {
|
||||
malformed = true;
|
||||
break;
|
||||
}
|
||||
@memcpy(checksum_bytes[set_bytes .. set_bytes + on_disk.entry_bytes], &fn_raw);
|
||||
set_bytes += on_disk.entry_bytes;
|
||||
const name_entry = std.mem.bytesToValue(on_disk.FileNameEntry, &fn_raw);
|
||||
for (name_entry.file_name) |unit| {
|
||||
if (name_len >= stream.name_length) break;
|
||||
if (name_len < name_buf.len) name_buf[name_len] = if (unit < 0x80) @truncate(unit) else '?';
|
||||
name_len += 1;
|
||||
}
|
||||
}
|
||||
const advance = @as(u64, file.secondary_count) + 1;
|
||||
if (malformed or on_disk.setChecksum(checksum_bytes[0..set_bytes]) != file.set_checksum) {
|
||||
index += advance;
|
||||
continue; // a set that does not check out is not a file
|
||||
}
|
||||
|
||||
const node = Node{
|
||||
.first_cluster = stream.first_cluster,
|
||||
.size = clampU32(stream.data_length),
|
||||
.is_directory = file.file_attributes & on_disk.attribute_directory != 0,
|
||||
.no_fat_chain = stream.general_secondary_flags & on_disk.secondary_flag_no_fat_chain != 0,
|
||||
.valid_data_length = clampU32(stream.valid_data_length),
|
||||
.mtime = on_disk.timestampToEpoch(file.last_modified_timestamp),
|
||||
.parent_first_cluster = dir.first_cluster,
|
||||
.parent_no_fat_chain = dir.no_fat_chain,
|
||||
.entry_index = index,
|
||||
.secondary_count = file.secondary_count,
|
||||
.has_entry = true,
|
||||
};
|
||||
if (visit(context, node, name_buf[0..@min(name_len, name_buf.len)])) return;
|
||||
index += advance;
|
||||
}
|
||||
}
|
||||
|
||||
const FindResult = struct { found: bool = false, node: Node = undefined };
|
||||
const FindContext = struct { fs: *FileSystem, query: []const u8, result: *FindResult };
|
||||
|
||||
fn findVisit(context: *FindContext, node: Node, name: []const u8) bool {
|
||||
if (!context.fs.nameMatches(name, context.query)) return false;
|
||||
context.result.* = .{ .found = true, .node = node };
|
||||
return true;
|
||||
}
|
||||
|
||||
fn findChild(self: *FileSystem, dir: Node, name: []const u8) ?Node {
|
||||
var result = FindResult{};
|
||||
var context = FindContext{ .fs = self, .query = name, .result = &result };
|
||||
self.scanDirectory(dir, &context, findVisit);
|
||||
return if (result.found) result.node else null;
|
||||
}
|
||||
|
||||
/// Resolve an absolute or "/"-relative path to a node. "/" is the root.
|
||||
pub fn resolve(self: *FileSystem, path: []const u8) ?Node {
|
||||
var node = self.rootNode();
|
||||
var it = std.mem.tokenizeScalar(u8, path, '/');
|
||||
while (it.next()) |component| {
|
||||
if (component.len == 0) continue;
|
||||
if (!node.is_directory) return null;
|
||||
node = self.findChild(node, component) orelse return null;
|
||||
}
|
||||
return node;
|
||||
}
|
||||
|
||||
const ListContext = struct { target: u32, index: u32 = 0, out: *Listing, done: bool = false };
|
||||
|
||||
fn listVisit(context: *ListContext, node: Node, name: []const u8) bool {
|
||||
if (context.index == context.target) {
|
||||
const n = @min(name.len, context.out.name_buffer.len);
|
||||
@memcpy(context.out.name_buffer[0..n], name[0..n]);
|
||||
context.out.name_len = n;
|
||||
context.out.is_directory = node.is_directory;
|
||||
context.out.size = node.size;
|
||||
context.out.mtime = node.mtime;
|
||||
context.done = true;
|
||||
return true;
|
||||
}
|
||||
context.index += 1;
|
||||
return false;
|
||||
}
|
||||
|
||||
/// The `cursor`th entry of a directory (for readdir): name, kind, size, mtime.
|
||||
pub fn listEntry(self: *FileSystem, dir: Node, cursor: u32) ?Listing {
|
||||
var listing = Listing{};
|
||||
var context = ListContext{ .target = cursor, .out = &listing };
|
||||
self.scanDirectory(dir, &context, listVisit);
|
||||
return if (context.done) listing else null;
|
||||
}
|
||||
|
||||
// --- read ---------------------------------------------------------------
|
||||
|
||||
/// Read up to `buffer.len` bytes of `node` from `offset`. Bytes at or past the
|
||||
/// stream's valid-data-length read as zero even though clusters are allocated.
|
||||
pub fn readFile(self: *FileSystem, node: Node, offset: u32, buffer: []u8) usize {
|
||||
if (offset >= node.size or !self.validCluster(node.first_cluster)) return 0;
|
||||
const want = @min(buffer.len, node.size - offset);
|
||||
const got = self.readChain(node.first_cluster, node.no_fat_chain, offset, buffer[0..want]);
|
||||
// Zero the region beyond valid_data_length (allocated but never written).
|
||||
if (offset + got > node.valid_data_length) {
|
||||
const zero_from: usize = if (offset >= node.valid_data_length) 0 else node.valid_data_length - offset;
|
||||
if (zero_from < got) @memset(buffer[zero_from..got], 0);
|
||||
}
|
||||
return got;
|
||||
}
|
||||
};
|
||||
|
||||
fn clampU32(value: u64) u32 {
|
||||
return @intCast(@min(value, @as(u64, std.math.maxInt(u32))));
|
||||
}
|
||||
|
||||
// --- tests: a RAM-backed exFAT image -----------------------------------------
|
||||
|
||||
const RamDisk = struct {
|
||||
bytes: []u8,
|
||||
fn readBlocks(context: *anyopaque, lba: u64, count: u32, buffer: []u8) bool {
|
||||
const self: *RamDisk = @ptrCast(@alignCast(context));
|
||||
const len = @as(usize, count) * sector_size;
|
||||
const start = lba * sector_size;
|
||||
if (start + len > self.bytes.len or buffer.len < len) return false;
|
||||
@memcpy(buffer[0..len], self.bytes[start .. start + len]);
|
||||
return true;
|
||||
}
|
||||
fn writeBlocks(context: *anyopaque, lba: u64, count: u32, buffer: []const u8) bool {
|
||||
const self: *RamDisk = @ptrCast(@alignCast(context));
|
||||
const len = @as(usize, count) * sector_size;
|
||||
const start = lba * sector_size;
|
||||
if (start + len > self.bytes.len or buffer.len < len) return false;
|
||||
@memcpy(self.bytes[start .. start + len], buffer[0..len]);
|
||||
return true;
|
||||
}
|
||||
fn device(self: *RamDisk) BlockDevice {
|
||||
return .{
|
||||
.context = self,
|
||||
.block_size = sector_size,
|
||||
.block_count = self.bytes.len / sector_size,
|
||||
.readBlocksFn = readBlocks,
|
||||
.writeBlocksFn = writeBlocks,
|
||||
};
|
||||
}
|
||||
};
|
||||
|
||||
// A minimal exFAT layout for the tests: 512-byte clusters (spc=1), FAT at sector
|
||||
// 8, cluster heap at sector 9. Cluster 2 = allocation bitmap, 3 = up-case table,
|
||||
// 4 = root. Two files: HELLO (contiguous, clusters 5-6) and SPLIT (fragmented,
|
||||
// clusters 7,9 linked through the FAT), each 1024 bytes (two clusters, so a read
|
||||
// crosses a cluster boundary).
|
||||
const test_clusters = 64;
|
||||
const test_fat_sector = 8;
|
||||
const test_heap_sector = 9;
|
||||
const test_read_bytes = 1024; // the two-cluster test files are 1024 bytes
|
||||
|
||||
fn testCluster(cluster: u32) usize {
|
||||
return (test_heap_sector + (cluster - 2)) * sector_size;
|
||||
}
|
||||
|
||||
fn writeFatEntry(bytes: []u8, cluster: u32, value: u32) void {
|
||||
std.mem.writeInt(u32, bytes[test_fat_sector * sector_size + cluster * 4 ..][0..4], value, .little);
|
||||
}
|
||||
|
||||
fn asciiUpper(c: u8) u16 {
|
||||
return if (c >= 'a' and c <= 'z') c - 'a' + 'A' else c;
|
||||
}
|
||||
|
||||
// Lay a File+Stream+Name set into the root at `entry_index`, naming `name` and
|
||||
// pointing at `first_cluster`/`length`, contiguous or FAT-linked.
|
||||
fn writeFileSet(bytes: []u8, entry_index: usize, name: []const u8, first_cluster: u32, length: u64, no_fat_chain: bool) void {
|
||||
const root = testCluster(4);
|
||||
var set: [on_disk.entry_bytes * 3]u8 = [_]u8{0} ** (on_disk.entry_bytes * 3);
|
||||
// File entry (0x85).
|
||||
set[0] = on_disk.entry_type_file;
|
||||
set[1] = 2; // stream + one name entry (names <= 15 units)
|
||||
std.mem.writeInt(u16, set[4..6], on_disk.attribute_archive, .little);
|
||||
// Stream entry (0xC0).
|
||||
const s = on_disk.entry_bytes;
|
||||
set[s + 0] = on_disk.entry_type_stream_extension;
|
||||
set[s + 1] = on_disk.secondary_flag_allocation_possible | (if (no_fat_chain) on_disk.secondary_flag_no_fat_chain else 0);
|
||||
set[s + 3] = @intCast(name.len); // name_length
|
||||
var upname: [name_maximum]u16 = undefined;
|
||||
for (name, 0..) |c, i| upname[i] = asciiUpper(c);
|
||||
std.mem.writeInt(u16, set[s + 4 ..][0..2], on_disk.nameHash(upname[0..name.len]), .little);
|
||||
std.mem.writeInt(u64, set[s + 8 ..][0..8], length, .little); // valid_data_length
|
||||
std.mem.writeInt(u32, set[s + 20 ..][0..4], first_cluster, .little);
|
||||
std.mem.writeInt(u64, set[s + 24 ..][0..8], length, .little); // data_length
|
||||
// File Name entry (0xC1).
|
||||
const f = on_disk.entry_bytes * 2;
|
||||
set[f + 0] = on_disk.entry_type_file_name;
|
||||
for (name, 0..) |c, i| std.mem.writeInt(u16, set[f + 2 + i * 2 ..][0..2], c, .little);
|
||||
// Set checksum (over all three entries, skipping its own two bytes).
|
||||
std.mem.writeInt(u16, set[2..4], on_disk.setChecksum(&set), .little);
|
||||
@memcpy(bytes[root + entry_index * on_disk.entry_bytes ..][0 .. on_disk.entry_bytes * 3], &set);
|
||||
}
|
||||
|
||||
fn formatExfat(bytes: []u8) void {
|
||||
@memset(bytes, 0);
|
||||
// VBR (sector 0).
|
||||
@memcpy(bytes[3..11], "EXFAT ");
|
||||
std.mem.writeInt(u64, bytes[72..80], bytes.len / sector_size, .little); // volume_length
|
||||
std.mem.writeInt(u32, bytes[80..84], test_fat_sector, .little); // fat_offset
|
||||
std.mem.writeInt(u32, bytes[84..88], 1, .little); // fat_length
|
||||
std.mem.writeInt(u32, bytes[88..92], test_heap_sector, .little); // cluster_heap_offset
|
||||
std.mem.writeInt(u32, bytes[92..96], test_clusters, .little); // cluster_count
|
||||
std.mem.writeInt(u32, bytes[96..100], 4, .little); // first_cluster_of_root
|
||||
std.mem.writeInt(u32, bytes[100..104], 0x1234ABCD, .little); // volume_serial_number
|
||||
bytes[108] = 9; // bytes_per_sector_shift = 512
|
||||
bytes[109] = 0; // sectors_per_cluster_shift = 1
|
||||
bytes[110] = 1; // number_of_fats
|
||||
bytes[510] = 0x55;
|
||||
bytes[511] = 0xAA;
|
||||
|
||||
// FAT: reserved entries + the chains that must be walkable.
|
||||
writeFatEntry(bytes, 0, 0xFFFFFFF8);
|
||||
writeFatEntry(bytes, 1, 0xFFFFFFFF);
|
||||
for ([_]u32{ 2, 3, 4, 5, 6 }) |c| writeFatEntry(bytes, c, 0xFFFFFFFF); // metadata + contiguous file (single-cluster chains / EOC)
|
||||
writeFatEntry(bytes, 7, 9); // SPLIT: cluster 7 -> 9
|
||||
writeFatEntry(bytes, 9, 0xFFFFFFFF); // SPLIT ends
|
||||
|
||||
// Allocation bitmap (cluster 2): clusters 2,3,4,5,6,7,9 in use.
|
||||
const bitmap = testCluster(2);
|
||||
for ([_]u32{ 2, 3, 4, 5, 6, 7, 9 }) |c| {
|
||||
const bit = c - 2;
|
||||
bytes[bitmap + bit / 8] |= @as(u8, 1) << @intCast(bit % 8);
|
||||
}
|
||||
|
||||
// Up-case table (cluster 3): 256 explicit units, a-z -> A-Z.
|
||||
const upcase = testCluster(3);
|
||||
var i: u32 = 0;
|
||||
while (i < upcase_fold_limit) : (i += 1) {
|
||||
std.mem.writeInt(u16, bytes[upcase + i * 2 ..][0..2], asciiUpper(@intCast(i)), .little);
|
||||
}
|
||||
const table_checksum = on_disk.upcaseChecksum(bytes[upcase .. upcase + upcase_fold_limit * 2]);
|
||||
|
||||
// Root directory (cluster 4): bitmap entry, up-case entry, then the two files.
|
||||
const root = testCluster(4);
|
||||
var bmp = std.mem.zeroes(on_disk.AllocationBitmapEntry);
|
||||
bmp.entry_type = on_disk.entry_type_allocation_bitmap;
|
||||
bmp.first_cluster = 2;
|
||||
bmp.data_length = (test_clusters + 7) / 8;
|
||||
@memcpy(bytes[root..][0..on_disk.entry_bytes], std.mem.asBytes(&bmp));
|
||||
var uct = std.mem.zeroes(on_disk.UpcaseTableEntry);
|
||||
uct.entry_type = on_disk.entry_type_upcase_table;
|
||||
uct.first_cluster = 3;
|
||||
uct.data_length = upcase_fold_limit * 2;
|
||||
uct.table_checksum = table_checksum;
|
||||
@memcpy(bytes[root + on_disk.entry_bytes ..][0..on_disk.entry_bytes], std.mem.asBytes(&uct));
|
||||
|
||||
writeFileSet(bytes, 2, "HELLO", 5, 1024, true); // contiguous (clusters 5-6)
|
||||
writeFileSet(bytes, 5, "SPLIT", 7, 1024, false); // fragmented (clusters 7,9)
|
||||
|
||||
// File contents: a distinct byte pattern per file, spanning both clusters.
|
||||
var b: usize = 0;
|
||||
while (b < 1024) : (b += 1) {
|
||||
bytes[testCluster(5) + b] = @truncate(b); // HELLO (5,6 contiguous)
|
||||
}
|
||||
b = 0;
|
||||
while (b < 512) : (b += 1) bytes[testCluster(7) + b] = @truncate(b +% 100); // SPLIT first cluster
|
||||
b = 0;
|
||||
while (b < 512) : (b += 1) bytes[testCluster(9) + b] = @truncate((b + 512) +% 100); // SPLIT second cluster
|
||||
}
|
||||
|
||||
test "mount an exFAT image and read its geometry + up-case table" {
|
||||
const allocator = std.testing.allocator;
|
||||
const bytes = try allocator.alloc(u8, 128 * sector_size);
|
||||
defer allocator.free(bytes);
|
||||
formatExfat(bytes);
|
||||
|
||||
var disk = RamDisk{ .bytes = bytes };
|
||||
var fs = FileSystem.mount(disk.device()) orelse return error.ShouldMount;
|
||||
try std.testing.expectEqual(@as(u32, 512), fs.geometry.bytes_per_sector);
|
||||
try std.testing.expectEqual(@as(u32, 4), fs.geometry.first_cluster_of_root);
|
||||
try std.testing.expectEqual(@as(u32, 2), fs.bitmap_first_cluster);
|
||||
// The up-case table loaded and folds ASCII.
|
||||
try std.testing.expectEqual(@as(u16, 'A'), fs.fold('a'));
|
||||
try std.testing.expectEqual(@as(u16, 'Z'), fs.fold('z'));
|
||||
try std.testing.expectEqual(@as(u16, '5'), fs.fold('5'));
|
||||
}
|
||||
|
||||
test "list the root directory (skipping the bitmap/up-case entries)" {
|
||||
const allocator = std.testing.allocator;
|
||||
const bytes = try allocator.alloc(u8, 128 * sector_size);
|
||||
defer allocator.free(bytes);
|
||||
formatExfat(bytes);
|
||||
var disk = RamDisk{ .bytes = bytes };
|
||||
var fs = FileSystem.mount(disk.device()).?;
|
||||
|
||||
const first = fs.listEntry(fs.rootNode(), 0).?;
|
||||
try std.testing.expectEqualStrings("HELLO", first.name_buffer[0..first.name_len]);
|
||||
try std.testing.expectEqual(@as(u32, 1024), first.size);
|
||||
const second = fs.listEntry(fs.rootNode(), 1).?;
|
||||
try std.testing.expectEqualStrings("SPLIT", second.name_buffer[0..second.name_len]);
|
||||
try std.testing.expect(fs.listEntry(fs.rootNode(), 2) == null);
|
||||
}
|
||||
|
||||
test "resolve is case-insensitive through the up-case table" {
|
||||
const allocator = std.testing.allocator;
|
||||
const bytes = try allocator.alloc(u8, 128 * sector_size);
|
||||
defer allocator.free(bytes);
|
||||
formatExfat(bytes);
|
||||
var disk = RamDisk{ .bytes = bytes };
|
||||
var fs = FileSystem.mount(disk.device()).?;
|
||||
|
||||
try std.testing.expect(fs.resolve("/hello") != null); // lower-case query matches HELLO
|
||||
try std.testing.expect(fs.resolve("/Hello") != null);
|
||||
try std.testing.expect(fs.resolve("/NOPE") == null);
|
||||
const node = fs.resolve("/HELLO").?;
|
||||
try std.testing.expectEqual(@as(u32, 5), node.first_cluster);
|
||||
try std.testing.expect(node.no_fat_chain);
|
||||
}
|
||||
|
||||
test "read a contiguous file across its cluster boundary" {
|
||||
const allocator = std.testing.allocator;
|
||||
const bytes = try allocator.alloc(u8, 128 * sector_size);
|
||||
defer allocator.free(bytes);
|
||||
formatExfat(bytes);
|
||||
var disk = RamDisk{ .bytes = bytes };
|
||||
var fs = FileSystem.mount(disk.device()).?;
|
||||
|
||||
const node = fs.resolve("/HELLO").?;
|
||||
var readback: [test_read_bytes]u8 = undefined;
|
||||
const got = fs.readFile(node, 0, &readback);
|
||||
try std.testing.expectEqual(@as(usize, 1024), got);
|
||||
for (readback, 0..) |byte, i| try std.testing.expectEqual(@as(u8, @truncate(i)), byte);
|
||||
}
|
||||
|
||||
test "read a fragmented file follows the FAT across non-contiguous clusters" {
|
||||
const allocator = std.testing.allocator;
|
||||
const bytes = try allocator.alloc(u8, 128 * sector_size);
|
||||
defer allocator.free(bytes);
|
||||
formatExfat(bytes);
|
||||
var disk = RamDisk{ .bytes = bytes };
|
||||
var fs = FileSystem.mount(disk.device()).?;
|
||||
|
||||
const node = fs.resolve("/SPLIT").?;
|
||||
try std.testing.expect(!node.no_fat_chain);
|
||||
var readback: [test_read_bytes]u8 = undefined;
|
||||
const got = fs.readFile(node, 0, &readback);
|
||||
try std.testing.expectEqual(@as(usize, 1024), got);
|
||||
// Cluster 7 held b+100; cluster 9 (the FAT-linked second) held (b+512)+100.
|
||||
for (readback, 0..) |byte, i| try std.testing.expectEqual(@as(u8, @truncate(i +% 100)), byte);
|
||||
// A mid-file read that starts in the second cluster still lands right.
|
||||
const mid = fs.readFile(node, 600, readback[0..10]);
|
||||
try std.testing.expectEqual(@as(usize, 10), mid);
|
||||
for (readback[0..10], 600..) |byte, i| try std.testing.expectEqual(@as(u8, @truncate(i +% 100)), byte);
|
||||
}
|
||||
Reference in New Issue
Block a user