Daniel Samson
c81120ef0f
The identity ladder's flag-day — no behavior change. partition.firstVolume stops
taking one preloaded block-0 slice and takes a SectorReader (a read-one-sector
fn), so it can reach GPT metadata at LBA 1 and each partition's VBR on demand
(the next commits). The u64 identity becomes Identity{rung,key,label}: key is the
id (the mount path derives from it), label is display metadata (empty at rung 4).
Identity equality is id-only (rung+key) — the label never enters it. Only rung-4
(MBR sig+index / bare-FAT index 0) is produced, byte-identical to before; the
four host tests port to a RAM-disk reader, and fat-mount/volume-probe/
volume-removal stay green.
350 lines
16 KiB
Zig
350 lines
16 KiB
Zig
//! system/services/volume-manager — the storage layer's policy home
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//! (docs/file-system-development/storage-architecture.md). Beside the device
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//! manager: that owns the DEVICE tree, this owns the VOLUME layer. It probes a
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//! storage provider's partition table, confines each filesystem to its
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//! partition, spawns one filesystem per volume, and answers that filesystem's
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//! startup hello with the range-confined block channel — so the filesystem
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//! never finds its storage by name and never sees the whole device. It
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//! supervises the filesystems it spawns, exactly as the device manager
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//! supervises drivers.
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//!
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//! This increment (V3b) is the flip: the FAT service stops acquiring its own
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//! volume and is spawned here instead, confined to its partition, and handed
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//! its channel over the volume-manager protocol. Single volume for now; the
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//! mount map (volumes.csv) and multi-volume land next.
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const std = @import("std");
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const channel = @import("channel");
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const device_manager_protocol = @import("device-manager-protocol");
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const volume_manager_protocol = @import("volume-manager-protocol");
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const driver = @import("driver");
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const ipc = @import("ipc");
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const block = @import("block");
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const memory = @import("memory");
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const logging = @import("logging");
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const process = @import("process");
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const service = @import("service");
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const time = @import("time");
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const envelope = @import("envelope");
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const partition = @import("partition.zig");
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const Serve = volume_manager_protocol.Protocol.Provider(void);
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const Invocation = envelope.Invocation;
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const Answer = envelope.Answer;
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/// The single volume this increment handles: its provider channel, its block
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/// sub-range, its identity, the id it is addressed by, and the filesystem
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/// process serving it (0 until spawned; reset on death for respawn).
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const Volume = struct {
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storage: block.Device,
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storage_device_id: u64, // the device-manager id this volume's provider serves
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base_lba: u64,
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block_count: u64,
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identity: partition.Identity,
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id: u64,
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filesystem_pid: u32 = 0,
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};
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/// The filesystem binary a probed volume is served by. The signature->binary
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/// map (filesystems.csv) lands with the identity ladder; for now every FAT-shaped
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/// volume gets the FAT service.
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const filesystem_binary = "/system/services/fat";
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const volume_id: u64 = 1;
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var service_endpoint: ipc.Handle = 0;
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var manager_handle: ?ipc.Handle = null;
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var bounce: memory.DmaRegion = undefined;
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var bounce_ready = false;
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/// The currently-mounted volume, or null while no storage is present. The whole
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/// removal lifecycle is this field going null and back: the poll sees the
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/// storage provider leave the device tree (a pulled stick), kills the filesystem
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/// and clears this; when it returns, the poll re-acquires and re-mounts.
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var volume: ?Volume = null;
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var logged_no_volume = false;
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/// How often the poll checks whether the storage provider is present. Fast
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/// enough that an unplug unmounts promptly; the poll is a bare device-manager
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/// enumerate, no channel work, so it is cheap to run continuously.
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const poll_interval_ms = 500;
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// Filesystem supervision, mirroring the device manager's (device-manager.zig):
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// a clean exit is not restarted, a fault restarts with backoff, and a fast
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// crash loop gives up rather than spinning. Without this a faulting filesystem
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// respawns in a zero-delay loop.
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const fast_death_ns: u64 = 2_000_000_000;
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const crash_loop_cap: u32 = 3;
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const backoff_base_ms: u64 = 300;
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var fs_restarts: u32 = 0;
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var fs_spawn_ns: u64 = 0;
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var fs_failed = false;
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/// A fat restart is due at `restart_due_ns`; the poll loop performs it once the
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/// backoff has elapsed (one timer, folded into the poll — no second timer).
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var restart_pending = false;
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var restart_due_ns: u64 = 0;
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fn deviceManager() ?ipc.Handle {
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if (manager_handle) |h| return h;
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const handle = channel.openEndpoint("device-manager") orelse return null;
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manager_handle = handle;
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return handle;
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}
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const OpenedStorage = struct { device_id: u64, device: block.Device };
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/// The first mass-storage provider whose block channel actually opens, with its
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/// device id. A device-manager tree can carry more than one entry of the
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/// mass-storage identity — a phantom that no driver is bound to answers a
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/// consumer hello with NO channel — so this tries each and takes the first that
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/// yields a channel, exactly as a filesystem's own acquisition loop does.
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/// Called only when there is no volume (an insertion), so the hellos it makes
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/// are not per-poll churn.
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fn openAnyStorage() ?OpenedStorage {
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const manager = deviceManager() orelse return null;
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const Entry = device_manager_protocol.ChildEntry;
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var start: u64 = 0;
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while (true) {
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const enumerate = envelope.Header{ .operation = envelope.operation_enumerate, .target = start };
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var reply: [device_manager_protocol.message_maximum]u8 = undefined;
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const length = ipc.call(manager, std.mem.asBytes(&enumerate), &reply) catch return null;
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const status = envelope.statusOf(reply[0..length]) orelse return null;
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if (status.status != 0) return null;
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const carried = @min(@as(usize, status.len), length -| envelope.prefix_size);
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const tail = reply[envelope.prefix_size..][0..carried];
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const count = tail.len / @sizeOf(Entry);
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if (count == 0) return null;
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var index: usize = 0;
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while (index < count) : (index += 1) {
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const entry = std.mem.bytesToValue(Entry, tail[index * @sizeOf(Entry) ..][0..@sizeOf(Entry)]);
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if (entry.device_id == device_manager_protocol.no_device) continue;
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if ((entry.identity >> 16) & 0xff != 0x08 or (entry.identity >> 8) & 0xff != 0x06) continue;
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const exchanged = driver.helloOn(manager, .consumer, entry.device_id, null, true) orelse continue;
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const provider = exchanged.channel orelse continue; // a phantom / not-yet-bound entry
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return .{ .device_id = entry.device_id, .device = .{ .endpoint = provider } };
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}
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start += count;
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}
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}
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/// Whether `device_id` is still in the device-manager tree — a bare enumerate,
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/// no consumer-hello, so it is cheap to call every poll. This is how removal is
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/// detected: the specific device the mounted volume sits on disappears.
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fn isDevicePresent(device_id: u64) bool {
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const manager = deviceManager() orelse return false;
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const Entry = device_manager_protocol.ChildEntry;
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var start: u64 = 0;
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while (true) {
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const enumerate = envelope.Header{ .operation = envelope.operation_enumerate, .target = start };
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var reply: [device_manager_protocol.message_maximum]u8 = undefined;
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const length = ipc.call(manager, std.mem.asBytes(&enumerate), &reply) catch return false;
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const status = envelope.statusOf(reply[0..length]) orelse return false;
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if (status.status != 0) return false;
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const carried = @min(@as(usize, status.len), length -| envelope.prefix_size);
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const tail = reply[envelope.prefix_size..][0..carried];
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const count = tail.len / @sizeOf(Entry);
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if (count == 0) return false;
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var index: usize = 0;
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while (index < count) : (index += 1) {
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const entry = std.mem.bytesToValue(Entry, tail[index * @sizeOf(Entry) ..][0..@sizeOf(Entry)]);
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if (entry.device_id == device_id) return true;
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}
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start += count;
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}
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}
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/// Spawn the filesystem for `v`, confine it to the volume's range, and record
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/// its pid. The confinement is defined for the fresh pid BEFORE the filesystem
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/// runs, so its first read is already bounded; the volume manager is the
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/// confinement controller (it defines the first range on the device).
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fn spawnFilesystem(v: *Volume) void {
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if (fs_failed) return;
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const pid = process.spawnSupervised(filesystem_binary, &.{"1"}, service_endpoint) orelse {
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_ = logging.write("volume-manager: could not spawn the filesystem; retrying\n");
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armRestart();
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return;
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};
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if (!v.storage.defineRange(pid, v.base_lba, v.block_count)) {
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_ = logging.write("volume-manager: could not confine the filesystem to its volume; retrying\n");
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_ = process.kill(pid);
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armRestart();
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return;
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}
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v.filesystem_pid = pid;
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fs_spawn_ns = time.clock();
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std.log.info("volume 0x{x} -> {s} (pid {d}), lba {d}, {d} blocks", .{ v.identity.key, filesystem_binary, pid, v.base_lba, v.block_count });
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}
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/// Schedule a fat restart after backoff; the poll loop performs it once due.
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fn armRestart() void {
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const delay = if (fs_restarts == 0) backoff_base_ms else backoff_base_ms << @intCast(@min(fs_restarts - 1, 5));
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restart_due_ns = time.clock() + delay * 1_000_000;
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restart_pending = true;
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}
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/// A storage provider just appeared: open its channel, read block 0, parse the
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/// volume, and spawn its filesystem. On any failure the channel is closed (so a
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/// present-but-unreadable device does not leak a handle every poll) and `volume`
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/// stays null — the next poll retries. A fresh medium gets a fresh supervision
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/// budget.
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fn bringUpVolume() void {
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if (!bounce_ready) {
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bounce = memory.dmaAlloc(512, memory.dma_coherent | memory.dma_shareable) orelse return;
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bounce_ready = true;
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}
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const opened = openAnyStorage() orelse return;
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const device = opened.device;
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// Attach the read buffer to THIS device (a no-op without an enforcing IOMMU).
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// The handle is kept, not closed, so it can be re-attached to the next
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// device after a replug.
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if (bounce.handle) |handle| {
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if (!device.attach(handle)) {
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_ = ipc.close(device.endpoint);
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return;
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}
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}
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const geometry = device.geometry() orelse {
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_ = ipc.close(device.endpoint);
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return;
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};
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const ProbeReader = struct {
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device: block.Device,
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fn readSector(context: *anyopaque, lba: u64, buffer: *[partition.sector_bytes]u8) bool {
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const self: *@This() = @ptrCast(@alignCast(context));
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if (!self.device.read(lba, 1, bounce.physical)) return false;
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const src: [*]const u8 = @ptrFromInt(bounce.virtual);
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@memcpy(buffer, src[0..partition.sector_bytes]);
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return true;
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}
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};
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var probe = ProbeReader{ .device = device };
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const reader = partition.SectorReader{ .context = &probe, .readFn = ProbeReader.readSector };
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const found = partition.firstVolume(reader, geometry.block_count) orelse {
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if (!logged_no_volume) {
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_ = logging.write("volume-manager: storage present but no recognizable volume\n");
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logged_no_volume = true;
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}
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_ = ipc.close(device.endpoint);
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return;
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};
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logged_no_volume = false;
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fs_restarts = 0;
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fs_failed = false;
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restart_pending = false;
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volume = .{ .storage = device, .storage_device_id = opened.device_id, .base_lba = found.base_lba, .block_count = found.block_count, .identity = found.identity, .id = volume_id };
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spawnFilesystem(&volume.?);
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}
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/// The storage provider left the device tree (a pulled stick): kill the
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/// filesystem so its mounts are retired. Retirement is lazy, not an eager
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/// death-time sweep — killing the process marks the filesystem's backend
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/// endpoint dead, and the VFS router drops each mount that endpoint backed on
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/// the next path resolution under it (that resolve frees the slot and returns
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/// not_found). Then drop the now-dead channel and clear the volume; the next
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/// poll that sees storage return re-mounts.
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fn removeVolume() void {
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const v = volume orelse return;
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std.log.info("storage for volume {d} removed; unmounting", .{v.id});
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if (v.filesystem_pid != 0) _ = process.kill(v.filesystem_pid);
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_ = ipc.close(v.storage.endpoint);
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volume = null;
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restart_pending = false;
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fs_restarts = 0;
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fs_failed = false;
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}
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/// One poll tick. Removal is checked FIRST and supersedes a pending restart: if
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/// the device is gone there is nothing to restart fat onto, and respawning it
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/// against the dead channel would just churn until the crash cap. Only once the
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/// device is confirmed present does a due restart fire.
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fn pollTick() void {
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if (volume) |v| {
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// Serving: watch for the specific device leaving (a pulled stick).
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if (!isDevicePresent(v.storage_device_id)) {
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removeVolume();
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return;
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}
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if (restart_pending and time.clock() >= restart_due_ns) {
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restart_pending = false;
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spawnFilesystem(&volume.?);
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}
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} else {
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// Idle: try to bring a present storage device up.
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bringUpVolume();
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}
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}
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/// A filesystem announces itself for the volume it was spawned to serve. Reply
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/// with that volume's block channel (already range-confined to this filesystem's
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/// badge) as the call's returned capability. No channel means the volume is not
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/// ready — the filesystem retries.
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fn onHello(_: void, invocation: Invocation(volume_manager_protocol.Hello), _: Answer(void)) isize {
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const v = volume orelse return 0; // not probed yet — retryable, no cap
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if (invocation.target != v.id) return 0; // unknown volume — retryable
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if (invocation.sender != v.filesystem_pid) {
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// Not the filesystem we spawned for this volume. Refuse: only the
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// confined filesystem gets the channel.
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std.log.info("refused hello for volume {d} from process {d}", .{ invocation.target, invocation.sender });
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return -envelope.EPERM;
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}
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service.replyWithCapability(v.storage.endpoint);
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std.log.info("handed volume {d} to pid {d}", .{ v.id, invocation.sender });
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return 0;
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}
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const handlers = Serve.Handlers{ .hello = onHello };
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fn onMessage(message: []const u8, out: []u8, sender: u32, arrived: *ipc.Arrival) usize {
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// No verb takes a capability up, so the turn closes whatever arrives.
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return Serve.dispatch({}, handlers, message, sender, arrived.peek(), out);
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}
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fn initialise(endpoint: ipc.Handle) bool {
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service_endpoint = endpoint;
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_ = logging.write("volume-manager: starting, waiting for a storage device\n");
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_ = process.subscribeExits(endpoint);
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pollTick();
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_ = time.timerOnce(endpoint, poll_interval_ms); // the poll runs for the life of the boot
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return true;
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}
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fn onNotification(badge: u64) void {
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const got = ipc.Received{ .len = 0, .badge = badge, .cap = null };
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if (got.isTimer()) {
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pollTick();
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_ = time.timerOnce(service_endpoint, poll_interval_ms); // always re-arm: presence is watched continuously
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return;
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}
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// A filesystem died. The exit reason drives the decision, exactly as the
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// device manager supervises drivers: a clean exit meant to stop; a fault
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// restarts with backoff until a fast crash loop gives up. The old range is
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// reclaimed by the driver on the same death; the respawn confines afresh.
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if (got.isChildExit()) {
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const dead = got.childProcessId();
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const v = &(volume orelse return);
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if (v.filesystem_pid != dead) return;
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v.filesystem_pid = 0;
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const reason = process.exitReason(dead) orelse .fault;
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if (reason == .exited) {
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std.log.info("filesystem for volume {d} exited cleanly; not restarting", .{v.id});
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return;
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}
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const alive = time.clock() -| fs_spawn_ns;
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fs_restarts = if (alive < fast_death_ns) fs_restarts + 1 else 1;
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if (fs_restarts >= crash_loop_cap) {
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fs_failed = true;
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std.log.info("filesystem for volume {d} is failing repeatedly; giving up", .{v.id});
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return;
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}
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std.log.info("filesystem for volume {d} died ({s}); restarting", .{ v.id, @tagName(reason) });
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armRestart();
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}
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}
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pub fn main(init: process.Init) void {
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_ = init;
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service.run(volume_manager_protocol.message_maximum, .{
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.service = "volume-manager",
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.init = initialise,
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.on_message = onMessage,
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.on_notification = onNotification,
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});
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}
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