A BUNCH OF STUFF

Metadata reading
Directory reading
Decompile cache
Actual SfsFile implementation
Finished Inode implementation
Actually build unsquashfs

src/decomp_cache.zig

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+const std = @import("std");
+const Io = std.Io;
+const File = Io.File;
+const MemoryMap = File.MemoryMap;
+const Atomic = std.atomic.Value;
+
+const Decomp = @import("decomp.zig");
+
+const DecompCache = @This();
+
+alloc: std.mem.Allocator,
+map: MemoryMap,
+decomp_fn: Decomp.Fn,
+
+cache: std.AutoHashMap(u64, Cache),
+mut: std.Io.RwLock = .init,
+cond: std.Io.Condition = .init,
+
+max_mem: u64,
+cur_mem: u64 = 0,
+
+pub fn init(alloc: std.mem.Allocator, map: MemoryMap, compression: Decomp.Enum, max_mem: u64) DecompCache {
+    return .{
+        .alloc = alloc,
+        .map = map,
+        .decomp_fn = try Decomp.DecompFn(compression),
+
+        .cache = .init(alloc),
+
+        .max_mem = max_mem,
+    };
+}
+pub fn deinit(self: *DecompCache, io: Io) void {
+    self.mut.lockUncancelable(io);
+
+    var iter = self.cache.valueIterator();
+    while (iter.next()) |v|
+        self.alloc.free(v.data);
+    self.cache.deinit();
+}
+
+pub fn get(self: *DecompCache, io: Io, offset: u64, compressed_size: u32, max_size: u32) ![]u8 {
+    {
+        try self.mut.lockShared(io);
+        defer self.mut.unlockShared(io);
+
+        const cache = self.cache.getPtr(offset);
+        if (cache != null) {
+            _ = cache.?.usage.fetchAdd(1, .acquire);
+            return cache.?.data;
+        }
+    }
+    try self.mut.lock(io);
+    defer self.mut.unlock(io);
+
+    const cache = try self.cache.getOrPut(offset);
+    if (cache.found_existing) {
+        _ = cache.?.usage.fetchAdd(1, .acquire);
+        return cache.?.data;
+    }
+    errdefer self.cache.removeByPtr(cache.key_ptr);
+
+    try self.ensureSpace(io, max_size);
+
+    var out = try self.alloc.alloc(u8, max_size);
+    errdefer self.alloc.free(out);
+
+    const decomp_size = try self.decomp_fn(self.alloc, self.map.memory[offset..][0..compressed_size], out);
+    if (decomp_size != max_size) {
+        if (!self.alloc.resize(out, decomp_size)) {
+            const new_out = try self.alloc.alloc(u8, decomp_size);
+            @memcpy(new_out, out[0..decomp_size]);
+            out = new_out;
+        } else {
+            out.len = decomp_size;
+        }
+    }
+    self.cur_mem += decomp_size;
+
+    cache.value_ptr.data = out;
+    _ = cache.value_ptr.usage.fetchAdd(1, .acquire);
+    return out;
+}
+pub fn finished(self: *DecompCache, io: Io, offset: u64) void {
+    const cache = self.cache.getPtr(offset);
+    if (cache == null) {
+        std.debug.print("Finished using cache, but cache does not exist: {}\n", .{offset});
+        return;
+    }
+    const use = cache.?.usage.fetchSub(1, .acquire);
+    if (use == 0)
+        self.cond.broadcast(io);
+}
+
+fn ensureSpace(self: *DecompCache, io: Io, size: u64) !void {
+    while (self.cur_mem + size > self.max_mem) {
+        var iter = self.cache.valueIterator();
+        while (iter.next()) |cache| {
+            if (cache.usage.load(.unordered) == 0) {
+                self.alloc.free(cache.data);
+                self.cur_mem -= cache.data.len;
+
+                if (self.cur_mem + size <= self.max_mem) return;
+            }
+        }
+        if (self.cur_mem + size <= self.max_mem) return;
+        try self.cond.wait(io, self.mut.mutex);
+    }
+}
+
+// Types
+
+const Cache = struct {
+    data: []u8,
+    usage: Atomic(u32),
+};