diff --git a/README.md b/README.md
index 7b2dcff608320cd4768b92be436dc19ceb4dbfdf..ca00752b05032c8f650850a9f546f711e7edc894 100644
--- a/README.md
+++ b/README.md
@@ -55,7 +55,7 @@ Any custom backend may also be used that defines the following functions:
 
 - `pub fn init() !void`
 - `pub fn deinit() void`
-- `pub fn init_thread() !void`
+- `pub fn init_thread(dir: std.fs.Dir) !void`
 - `pub fn deinit_thread() void`
 - `pub inline fn trace_begin(ctx: tracer.Ctx, comptime ifmt: []const u8, iargs: anytype) void`
 - `pub inline fn trace_end(ctx: tracer.Ctx) void`
diff --git a/src/chrome.zig b/src/chrome.zig
index b8bd32b0e72228ca8d93e092c7b07fef18411288..8ad286fb92902b5a9f632590bf17f7b5abdeace7 100644
--- a/src/chrome.zig
+++ b/src/chrome.zig
@@ -19,11 +19,11 @@ pub fn deinit() void {
     //
 }
 
-pub fn init_thread() !void {
+pub fn init_thread(dir: std.fs.Dir) !void {
     tid = std.os.linux.gettid();
 
-    path = try std.fmt.allocPrint(alloc, "/data/trace.{d}.{d}.chrome.json", .{ pid, tid });
-    file = try std.fs.cwd().createFile(path, .{});
+    path = try std.fmt.allocPrint(alloc, "trace.{d}.{d}.chrome.json", .{ pid, tid });
+    file = try dir.createFile(path, .{});
     buffered_writer = std.io.bufferedWriter(file.writer());
 
     try buffered_writer.writer().writeAll("[\n");
diff --git a/src/log.zig b/src/log.zig
index 056529e536cfcb36f0a2de9e762d2ddd49eb2229..dad5459b769347bf9589887b4f9753e773c62271 100644
--- a/src/log.zig
+++ b/src/log.zig
@@ -6,7 +6,9 @@ pub fn init() !void {}
 
 pub fn deinit() void {}
 
-pub fn init_thread() !void {}
+pub fn init_thread(dir: std.fs.Dir) !void {
+    _ = dir;
+}
 
 pub fn deinit_thread() void {}
 
diff --git a/src/main.zig b/src/main.zig
index 7c9ac56c20fbfc3b3350992db65e9653586deda4..78dc47ea672ac67db7abd7d3c475eca367239aaa 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -17,7 +17,7 @@ pub fn main() !void {
     // main loop
     var go = false;
     while (go) {
-        try tracer.init_thread();
+        try tracer.init_thread(std.fs.cwd());
         defer tracer.deinit_thread();
 
         handler();
diff --git a/src/mod.zig b/src/mod.zig
index f4674b0b6ec79a4e2e39617b15c58eb8b105d6cf..e8b62566bfef61074737bb58fa4bb72f33dc1834 100644
--- a/src/mod.zig
+++ b/src/mod.zig
@@ -17,8 +17,8 @@ pub fn deinit() void {
     impl.deinit();
 }
 
-pub fn init_thread() !void {
-    try impl.init_thread();
+pub fn init_thread(dir: ?std.fs.Dir) !void {
+    try impl.init_thread(dir orelse std.fs.cwd());
     started = true;
 }
 
diff --git a/src/none.zig b/src/none.zig
index 29ef21951d60822d6bd22926aebe5f7b9f656c96..355ad7981015ac088025e564702ddb4165134ec7 100644
--- a/src/none.zig
+++ b/src/none.zig
@@ -6,7 +6,9 @@ pub fn init() !void {}
 
 pub fn deinit() void {}
 
-pub fn init_thread() !void {}
+pub fn init_thread(dir: std.fs.Dir) !void {
+    _ = dir;
+}
 
 pub fn deinit_thread() void {}
 
diff --git a/src/spall.zig b/src/spall.zig
index fe48e99b0888ac949667aa57038dac9a542043b0..65a4f7e82569b3cbadc833822aa1bad262b0dbb2 100644
--- a/src/spall.zig
+++ b/src/spall.zig
@@ -19,11 +19,11 @@ pub fn deinit() void {
     //
 }
 
-pub fn init_thread() !void {
+pub fn init_thread(dir: std.fs.Dir) !void {
     tid = std.os.linux.gettid();
 
-    path = try std.fmt.allocPrint(alloc, "/data/trace.{d}.{d}.spall", .{ pid, tid });
-    file = try std.fs.cwd().createFile(path, .{});
+    path = try std.fmt.allocPrint(alloc, "{d}.{d}.spall", .{ pid, tid });
+    file = try dir.createFile(path, .{});
     buffered_writer = std.io.bufferedWriter(file.writer());
 
     try buffered_writer.writer().writeStruct(Header{});