250 lines
12 KiB
Zig
250 lines
12 KiB
Zig
//! system/services/fat — the FAT filesystem server. Spawned as a boot service, it
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//! opens the block device (a USB stick via usb-storage) under `.block`, mounts the
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//! FAT filesystem on it (the pure engine in engine.zig), and mounts itself into
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//! the VFS at /mnt/usb. From then on the VFS forwards every open/read/write/
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//! status/readdir/close under /mnt/usb to this server, which serves the same
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//! vfs-protocol as a backend — turning block reads into file reads.
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//!
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//! The block data path never crosses IPC: a DMA bounce buffer is handed to the
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//! block driver by physical address, and the engine copies sectors in and out of
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//! it.
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const std = @import("std");
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const runtime = @import("runtime");
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const engine = @import("engine.zig");
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const on_disk = @import("on-disk.zig");
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const protocol = runtime.vfs_protocol;
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const dma = runtime.dma;
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fn writeLine(comptime fmt: []const u8, arguments: anytype) void {
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var line: [96]u8 = undefined;
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_ = runtime.system.write(std.fmt.bufPrint(&line, fmt, arguments) catch return);
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}
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const mount_point = "/mnt/usb";
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// The engine's BlockDevice, backed by the `.block` driver plus a DMA bounce
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// buffer the driver reads/writes by physical address.
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const IpcBlock = struct {
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device: runtime.block.Device,
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bounce: dma.Region,
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fn readBlock(context: *anyopaque, lba: u64, buffer: []u8) bool {
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const self: *IpcBlock = @ptrCast(@alignCast(context));
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if (!self.device.read(lba, 1, self.bounce.physical)) return false;
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const source: [*]const u8 = @ptrFromInt(self.bounce.virtual);
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@memcpy(buffer[0..512], source[0..512]);
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return true;
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}
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fn writeBlock(context: *anyopaque, lba: u64, buffer: []const u8) bool {
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const self: *IpcBlock = @ptrCast(@alignCast(context));
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const destination: [*]u8 = @ptrFromInt(self.bounce.virtual);
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@memcpy(destination[0..512], buffer[0..512]);
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if (!self.device.write(lba, 1, self.bounce.physical)) return false;
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device_dirty = true; // a block reached the device; a close will flush it
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return true;
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}
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};
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var ipc_block: IpcBlock = undefined;
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// Set whenever a block is written, cleared when the device cache is flushed on a
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// file close — so writes are committed to stable media before a power-off.
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var device_dirty: bool = false;
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var filesystem: engine.FileSystem = undefined;
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// Open handles the VFS holds against this backend: each maps a node id to a
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// resolved engine node.
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const OpenNode = struct { used: bool = false, node: engine.Node = undefined, owner: u32 = 0 };
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var open_nodes = [_]OpenNode{.{}} ** 32;
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fn allocOpen() ?usize {
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for (&open_nodes, 0..) |*o, i| {
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if (!o.used) return i;
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}
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return null;
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}
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fn openAt(id: u64) ?*OpenNode {
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if (id >= open_nodes.len) return null;
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const o = &open_nodes[@intCast(id)];
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return if (o.used) o else null;
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}
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fn writeReply(out: []u8, reply: protocol.Reply, payload: []const u8) usize {
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@memcpy(out[0..protocol.reply_size], std.mem.asBytes(&reply));
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const n = @min(payload.len, out.len - protocol.reply_size);
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@memcpy(out[protocol.reply_size..][0..n], payload[0..n]);
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return protocol.reply_size + n;
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}
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fn fail(out: []u8) usize {
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return writeReply(out, .{ .status = -1 }, &.{});
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}
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fn initialise(endpoint: runtime.ipc.Handle) bool {
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_ = runtime.system.write("/system/services/fat: starting, waiting for a block device\n");
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const device = runtime.block.open() orelse {
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_ = runtime.system.write("/system/services/fat: no block device (no storage attached)\n");
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return false; // clean exit: nothing to serve
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};
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const geometry = device.geometry() orelse {
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_ = runtime.system.write("/system/services/fat: block geometry unavailable\n");
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return false;
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};
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ipc_block = .{ .device = device, .bounce = dma.alloc(4096, dma.coherent) orelse return false };
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const block_device = engine.BlockDevice{
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.context = &ipc_block,
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.block_size = geometry.block_size,
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.block_count = geometry.block_count,
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.readBlockFn = IpcBlock.readBlock,
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.writeBlockFn = IpcBlock.writeBlock,
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};
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filesystem = engine.FileSystem.mount(block_device) orelse {
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_ = runtime.system.write("/system/services/fat: not a FAT filesystem\n");
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return false;
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};
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writeLine("/system/services/fat: mounted FAT ({s}, {d} clusters, partition lba {d})\n", .{ @tagName(filesystem.geometry.fat_type), filesystem.geometry.cluster_count, filesystem.base_lba });
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// Mount ourselves into the VFS namespace at /mnt/usb (retry while the VFS
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// comes up). From here the VFS routes /mnt/usb/... to this server.
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var tries: u32 = 0;
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while (tries < 100) : (tries += 1) {
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if (runtime.fs.mount(mount_point, endpoint)) {
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writeLine("/system/services/fat: mounted {s}\n", .{mount_point});
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return true;
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}
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runtime.system.sleep(50);
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}
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_ = runtime.system.write("/system/services/fat: could not mount into the VFS\n");
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return true; // still serve directly, even if the namespace mount didn't take
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}
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const ParentLeaf = struct { parent: []const u8, leaf: []const u8 };
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// Split a path into its parent directory and final component: "/a/b" -> ("/a",
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// "b"); "/b" -> ("/", "b"); "b" -> ("/", "b").
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fn splitParent(path: []const u8) ParentLeaf {
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const slash = std.mem.lastIndexOfScalar(u8, path, '/');
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return .{
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.parent = if (slash) |s| (if (s == 0) "/" else path[0..s]) else "/",
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.leaf = if (slash) |s| path[s + 1 ..] else path,
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};
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}
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fn handleOpen(out: []u8, path: []const u8, flags: u32) usize {
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var node = filesystem.resolve(path);
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if (node == null and flags & protocol.create != 0) {
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const split = splitParent(path);
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const parent = filesystem.resolve(split.parent) orelse return fail(out);
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node = filesystem.createFile(parent, split.leaf);
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}
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var resolved = node orelse return fail(out);
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// O_TRUNC: replace an existing file's contents rather than overwriting in place
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// (frees the old chain, so a shorter rewrite leaves no stale tail).
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if (flags & protocol.truncate != 0 and !resolved.is_directory) {
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filesystem.truncate(&resolved);
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}
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const index = allocOpen() orelse return fail(out);
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open_nodes[index] = .{ .used = true, .node = resolved };
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return writeReply(out, .{ .status = 0, .node = index }, &.{});
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}
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fn onMessage(message: []const u8, out: []u8, sender: u32, capability: ?runtime.ipc.Handle) usize {
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_ = capability;
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_ = sender;
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if (message.len < protocol.request_size) return fail(out);
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const request = std.mem.bytesToValue(protocol.Request, message[0..protocol.request_size]);
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const payload = message[protocol.request_size..];
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// Stamp create/write with the current wall-clock time (mtime). Cheap, and it
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// keeps the engine pure (it takes the time as data, not a syscall).
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filesystem.current_time_epoch = runtime.system.wallClock();
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switch (request.operation) {
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.open => return handleOpen(out, payload[0..@min(payload.len, request.len)], request.flags),
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.read => {
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const o = openAt(request.node) orelse return fail(out);
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var buffer: [protocol.maximum_payload]u8 = undefined;
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const want = @min(@as(usize, request.len), buffer.len);
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const n = filesystem.readFile(o.node, @intCast(request.offset), buffer[0..want]);
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return writeReply(out, .{ .status = 0, .len = @intCast(n) }, buffer[0..n]);
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},
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.write => {
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const o = openAt(request.node) orelse return fail(out);
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const data = payload[0..@min(payload.len, request.len)];
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const n = filesystem.writeFile(&o.node, @intCast(request.offset), data);
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return writeReply(out, .{ .status = 0, .len = @intCast(n) }, &.{});
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},
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.status => {
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const o = openAt(request.node) orelse return fail(out);
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const kind: protocol.NodeKind = if (o.node.is_directory) .directory else .regular;
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const status = protocol.FileStatus{ .size = o.node.size, .kind = @intFromEnum(kind), .mtime = o.node.mtime };
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return writeReply(out, .{ .status = 0, .len = @sizeOf(protocol.FileStatus) }, std.mem.asBytes(&status));
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},
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.readdir => {
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const o = openAt(request.node) orelse return fail(out);
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if (!o.node.is_directory) return writeReply(out, .{ .status = 0, .len = 0 }, &.{});
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const listing = filesystem.listEntry(o.node, @intCast(request.offset)) orelse return writeReply(out, .{ .status = 0, .len = 0 }, &.{});
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const kind: protocol.NodeKind = if (listing.is_directory) .directory else .regular;
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const header = protocol.DirectoryEntry{ .kind = @intFromEnum(kind), .name_len = @intCast(listing.name_len), .size = listing.size };
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var buffer: [protocol.maximum_payload]u8 = undefined;
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@memcpy(buffer[0..protocol.directory_entry_size], std.mem.asBytes(&header));
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const nlen = @min(listing.name_len, buffer.len - protocol.directory_entry_size);
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@memcpy(buffer[protocol.directory_entry_size..][0..nlen], listing.name_buffer[0..nlen]);
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const total = protocol.directory_entry_size + nlen;
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return writeReply(out, .{ .status = 0, .len = @intCast(total) }, buffer[0..total]);
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},
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.close => {
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if (openAt(request.node)) |o| o.used = false;
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// Durable-on-close: if any block reached the device since the last
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// flush, commit its cache to stable media now (best-effort). This is
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// what makes init's shutdown log flush survive a real power-off, and is
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// the right default for removable media the user may unplug.
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if (device_dirty) {
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_ = ipc_block.device.flush();
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device_dirty = false;
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}
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return writeReply(out, .{ .status = 0 }, &.{});
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},
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.mkdir => {
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const split = splitParent(payload[0..@min(payload.len, request.len)]);
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const parent = filesystem.resolve(split.parent) orelse return fail(out);
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if (filesystem.createDirectory(parent, split.leaf) == null) return fail(out);
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return writeReply(out, .{ .status = 0 }, &.{});
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},
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.unlink => {
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const split = splitParent(payload[0..@min(payload.len, request.len)]);
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const parent = filesystem.resolve(split.parent) orelse return fail(out);
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if (!filesystem.removeFile(parent, split.leaf)) return fail(out);
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return writeReply(out, .{ .status = 0 }, &.{});
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},
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.rename => {
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const both = payload[0..@min(payload.len, request.len)];
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const sep = std.mem.indexOfScalar(u8, both, 0) orelse return fail(out);
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const old_split = splitParent(both[0..sep]);
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const new_split = splitParent(both[sep + 1 ..]);
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// Same-directory rename only.
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if (!std.mem.eql(u8, old_split.parent, new_split.parent)) return fail(out);
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const parent = filesystem.resolve(old_split.parent) orelse return fail(out);
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if (!filesystem.rename(parent, old_split.leaf, new_split.leaf)) return fail(out);
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return writeReply(out, .{ .status = 0 }, &.{});
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},
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// A backend is never itself a mount target.
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.mount, .unmount => return fail(out),
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}
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}
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pub fn main() void {
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runtime.service.run(protocol.message_maximum, .{
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.service = .fat,
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.init = initialise,
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.on_message = onMessage,
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});
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}
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pub const panic = runtime.panic;
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comptime {
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_ = &runtime.start._start;
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}
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