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[WasmFS] Skip mounting special files under NODERAWFS #26607

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[WasmFS] Skip mounting special files under NODERAWFS #26607

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50159b1
[WasmFS] Skip mounting special files under NODERAWFS
kleisauke Mar 25, 2026
e1da2f5
Automatic rebaseline of codesize expectations. NFC
kleisauke Apr 2, 2026
f3b85c9
Incorporate feedback
kleisauke Apr 2, 2026
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2 changes: 2 additions & 0 deletions system/lib/wasmfs/backend.h
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,8 @@ class Backend {
virtual std::shared_ptr<Directory> createDirectory(mode_t mode) = 0;
virtual std::shared_ptr<Symlink> createSymlink(std::string target) = 0;

virtual bool shouldMountSpecialFiles() { return true; }
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@sbc100 sbc100 Apr 2, 2026

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I was thinking maybe shouldPopulateRoot, but maybe your name is more explicit?

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@kleisauke kleisauke Apr 2, 2026

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This function name was mentioned in comment #24733 (comment). But I'd like shouldPopulateRoot as well.


virtual ~Backend() = default;
};

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2 changes: 2 additions & 0 deletions system/lib/wasmfs/backends/node_backend.cpp
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Expand Up @@ -294,6 +294,8 @@ class NodeBackend : public Backend {
std::shared_ptr<Symlink> createSymlink(std::string target) override {
WASMFS_UNREACHABLE("TODO: implement NodeBackend::createSymlink");
}

virtual bool shouldMountSpecialFiles() override { return false; }
};

// TODO: symlink
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7 changes: 6 additions & 1 deletion system/lib/wasmfs/wasmfs.cpp
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Expand Up @@ -106,8 +106,13 @@ std::shared_ptr<Directory> WasmFS::initRootDirectory() {
// The root directory is its own parent.
lockedRoot.setParent(rootDirectory);

// Don't mount special files if not needed (e.g. in NODERAWFS mode).
if (!rootBackend->shouldMountSpecialFiles()) {
return rootDirectory;
}

// If the /dev/ directory does not already exist, create it. (It may already
// exist in NODERAWFS mode, or if those files have been preloaded.)
// exist if those files have been preloaded.)
auto devDir = lockedRoot.insertDirectory("dev", S_IRUGO | S_IXUGO);
if (devDir) {
auto lockedDev = devDir->locked();
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8 changes: 4 additions & 4 deletions test/codesize/test_codesize_cxx_wasmfs.json
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Original file line number Diff line number Diff line change
@@ -1,10 +1,10 @@
{
"a.out.js": 7023,
"a.out.js.gz": 3310,
"a.out.nodebug.wasm": 172714,
"a.out.nodebug.wasm.gz": 63316,
"total": 179737,
"total_gz": 66626,
"a.out.nodebug.wasm": 172741,
"a.out.nodebug.wasm.gz": 63348,
"total": 179764,
"total_gz": 66658,
"sent": [
"__cxa_throw",
"_abort_js",
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8 changes: 4 additions & 4 deletions test/codesize/test_codesize_files_wasmfs.json
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Original file line number Diff line number Diff line change
@@ -1,10 +1,10 @@
{
"a.out.js": 5465,
"a.out.js.gz": 2575,
"a.out.nodebug.wasm": 58418,
"a.out.nodebug.wasm.gz": 18067,
"total": 63883,
"total_gz": 20642,
"a.out.nodebug.wasm": 58443,
"a.out.nodebug.wasm.gz": 18094,
"total": 63908,
"total_gz": 20669,
"sent": [
"a (emscripten_date_now)",
"b (emscripten_err)",
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4 changes: 4 additions & 0 deletions test/test_other.py
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Expand Up @@ -5553,6 +5553,8 @@ def test_fsync(self, args):
def test_fs_dev_random(self):
if WINDOWS and self.get_setting('NODERAWFS'):
self.skipTest('Crashes on Windows and NodeFS')
if self.get_setting('NODERAWFS') and self.get_setting('WASMFS'):
self.skipTest('https://github.com/emscripten-core/emscripten/issues/24830')
self.do_runf('fs/test_fs_dev_random.c', 'success')

@parameterized({
Expand Down Expand Up @@ -13256,6 +13258,8 @@ def test_unistd_chown(self):

@wasmfs_all_backends
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@sbc100 sbc100 Apr 2, 2026

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Why remove this?

Does wasmfs_getdents.c need to get re-written to handle the rawfs mabye?

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@sbc100 sbc100 Apr 2, 2026

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Should we just skip under NODERAWFS rather than removing wasmfs_all_backends completely?

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@kleisauke kleisauke Apr 2, 2026

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I re-added the @wasmfs_all_backends decorator and skipped this only under NODERAWFS with commit f3b85c9.

See for details:

emscripten/test/wasmfs/wasmfs_getdents.out

Lines 51 to 59 in 34f6bcf

------------- Reading from /dev Directory via JS -------------
.
..
null
random
stderr
stdin
stdout
urandom

def test_wasmfs_getdents(self):
if self.get_setting('NODERAWFS'):
self.skipTest('test expectations assumes /dev is virtualized')
# Run only in WASMFS for now.
self.set_setting('FORCE_FILESYSTEM')
self.do_run_in_out_file_test('wasmfs/wasmfs_getdents.c')
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