[WasmFS] Fix absolute path access under NODERAWFS by kleisauke · Pull Request #24733 · emscripten-core/emscripten

kleisauke · 2025-07-17T19:38:33Z

Resolves: #24830.
Supersedes: #24833.

See: emscripten-core/emscripten#24733.

This reverts commit 88df6ba.

kleisauke · 2026-03-24T16:03:13Z

Marking as ready for review with a few caveats:

~~wasmfs.test_readdir_rawfs appears to be failing.~~ Edit: see comment below.
It also fails in the wasm-vips Windows CI when writing to C:\Users\RUNNER~1\AppData\Local\Temp, see:
https://github.com/kleisauke/wasm-vips/actions/runs/23491851397/job/68365978350
(this was workarounded in commit kleisauke/wasm-vips@52f2d3c) Edit: see comment below.
Code size expectations need to be rebaselined.
~~Some changes could be split into separate PRs.~~ Edit: done.

This reverts commit 88df6ba.

kleisauke · 2026-03-25T16:00:08Z

The Windows CI issue was caused due to the temporary directory being located on C:\ while the current working directory was on D:\, which broke WasmFS's single-root (/) assumption.

This has been fixed in commit d364aeb, which also appears to resolve the test failure in wasmfs.test_readdir_rawfs.

system/lib/wasmfs/backends/node_backend.cpp

tlively · 2026-04-01T17:05:50Z

system/lib/wasmfs/paths.cpp

+  if (!root->getBackend()->isVirtualized()) {
+    return {std::make_pair(std::move(curr), path)};


The whole point of virtualization is that a virtual backend looks the same as a "real" backend. Can we get away without this part of the change?

IIRC, this change was related to -sNODERAWFS on Windows, which doesn't have a single-root directory

I initially attempted a different fix (see e.g. the changes before commit d364aeb), but it failed when the current working directory and the absolute path to be accessed were on different drives, see comment #24733 (comment).

I renamed this isVirtualized() check with a requiresPathTraversal() check via commit cb9bb3e.

tlively · 2026-04-01T17:07:44Z

system/lib/wasmfs/wasmfs.cpp

+  if (!rootBackend->isVirtualized()) {
+    return rootDirectory;
+  }


Let's use a more precise overridable hook here, e.g. shouldMountSpecialFiles, rather than checking whether the backend is virtual.

I've just separated this change to PR #26607.

tlively · 2026-04-01T17:12:10Z

src/lib/libwasmfs_node.js

Are all the changes here just cleanups that are not directly related to the absolute path access problem?

Yup, I've just separated these changes into individual PRs.

tlively · 2026-04-01T17:12:22Z

src/lib/libwasmfs_node.js


 addToLibrary({
-  $wasmfsNodeIsWindows: !!process.platform.match(/^win/),
+#if !ENVIRONMENT_MAY_BE_NODE


What's the goal of this change?

This change was to allow a single Wasm binary to run both on Node.js and on the web (if you build with -sWASMFS -sNODERAWFS the Wasm binary is restricted to Node.js only).

I reverted this (and its test case) with commit ff4bba2. A PR will be opened for this later.

... I just opened PR #26608 for this change.

In line with commit f1dfaf3. Split out from #24733.

In line with commit c77be74. Split out from #24733.

Resolves: emscripten-core#24830.

Split out from #24733, this fixes a test failure in `other.test_fs_dev_random_wasmfs_rawfs` from that PR.

See commit 48459c6 for details. Split out from #24733, this fixes a test failure in `core0.test_fs_js_api_wasmfs_rawfs` from that PR.

tlively

Thanks for splitting this up. It's much more focused and easier to review now. Mostly LGTM, with some bikeshedding and a correctness concern.

tlively · 2026-04-03T00:28:35Z

system/lib/wasmfs/backends/node_backend.cpp

    WASMFS_UNREACHABLE("TODO: implement NodeBackend::createSymlink");
  }
+
+  virtual bool requiresPathTraversal() override {


How about calling this usesRawPaths? (And flipping the result, of course.) I think that's slightly easier to understand than requiresPathTraversal, though it's not perfect.

I think usesRawPaths it's too implementation-specific. How about requiresPathResolution? See commit e21bc63.

tlively · 2026-04-03T00:33:14Z

system/lib/wasmfs/paths.cpp

+  // full path directly. In that case, skip WasmFS path parsing and pass the
+  // path through unchanged.
+  if (!root->getBackend()->requiresPathTraversal()) {
+    return {std::make_pair(std::move(curr), path)};


Is this going to cause WasmFS to model the underlying file system as completely flat, so that there is a single mount directory directly containing every file ever opened, no matter how deep that file is in the underlying directory structure?

If so, is that going to cause problems with reading directory entries?

Indeed, this is going to break in such situations as it implicitly assumes that the entire file system behaves like the root backend.

Commit e21bc63 changes this to curr->getBackend() instead, which allows:

$ tree / -L 2 --dirsfirst / (MEMFS) ├── dev │ ├── null -> SpecialFiles::getNull() │ ├── random -> SpecialFiles::getRandom() │ ├── stderr -> SpecialFiles::getStderr() │ ├── stdin -> SpecialFiles::getStdin() │ ├── stdout -> SpecialFiles::getStdout() │ └── urandom -> SpecialFiles::getURandom() ├── tmp └── host (NODERAWFS)

(i.e. the Node filesystem is mounted under /host, while the wasmfs_create_root_dir() hook is not overriden)

Split out from #24733.

Previously, the WasmFS Node backend assumed Node.js was always available. This change allows building binaries that include Node backend stubs, so they can run in web environments. Split out from #24733.

kleisauke added a commit to kleisauke/wasm-vips that referenced this pull request Jul 18, 2025

[WiP] Try to fix non-Linux CI

fe2267f

See: emscripten-core/emscripten#24733.

kleisauke mentioned this pull request Jul 31, 2025

WasmFS NodeRawFS is not consistent with NodeRawFS (non-WasmFS version) #24830

Open

kleisauke force-pushed the wasmfs-noderawfs-abspath branch from 539e100 to 4c2d596 Compare March 23, 2026 18:06

kleisauke changed the title ~~[WasmFS] Add testcases for absolute path handling with NODERAWFS~~ [WasmFS] Fix absolute path access under NODERAWFS Mar 23, 2026

kleisauke force-pushed the wasmfs-noderawfs-abspath branch 4 times, most recently from 99a1e0d to fd7f0a9 Compare March 24, 2026 12:17

kleisauke added a commit to kleisauke/wasm-vips that referenced this pull request Mar 24, 2026

Update for emscripten-core/emscripten#24733

4a8c45c

This reverts commit 88df6ba.

kleisauke marked this pull request as ready for review March 24, 2026 16:03

kleisauke added a commit to kleisauke/wasm-vips that referenced this pull request Mar 25, 2026

Update for emscripten-core/emscripten#24733

ef3bbe1

This reverts commit 88df6ba.

tlively reviewed Apr 1, 2026

View reviewed changes

sbc100 pushed a commit that referenced this pull request Apr 1, 2026

[WasmFS] Simplify cDefs in the Node backend. NFC (#26594)

fcff6d8

In line with commit f1dfaf3. Split out from #24733.

sbc100 pushed a commit that referenced this pull request Apr 1, 2026

[WasmFS] Simplify read/write in the Node backend. NFC (#26595)

d362b72

In line with commit c77be74. Split out from #24733.

kleisauke mentioned this pull request Apr 2, 2026

[WasmFS] Skip mounting special files under NODERAWFS #26607

Open

kleisauke added 2 commits April 2, 2026 10:09

[WasmFS] Fix absolute path access under NODERAWFS

a6e22e4

Resolves: emscripten-core#24830.

Add comments

f04892c

kleisauke force-pushed the wasmfs-noderawfs-abspath branch 2 times, most recently from b1edba4 to 4f20a95 Compare April 2, 2026 08:41

Rename isVirtualized() to requiresPathTraversal()

cb9bb3e

kleisauke force-pushed the wasmfs-noderawfs-abspath branch from 4f20a95 to cb9bb3e Compare April 2, 2026 08:48

kleisauke mentioned this pull request Apr 2, 2026

[WasmFS] Make the Node backend optional for web builds #26608

Merged

sbc100 pushed a commit that referenced this pull request Apr 2, 2026

[WasmFS] Allow reading from char devices in the Node backend (#26599)

bc56904

Split out from #24733, this fixes a test failure in `other.test_fs_dev_random_wasmfs_rawfs` from that PR.

sbc100 pushed a commit that referenced this pull request Apr 2, 2026

[WasmFS] Ensure error codes are negative in the Node backend (#26598)

34f6bcf

See commit 48459c6 for details. Split out from #24733, this fixes a test failure in `core0.test_fs_js_api_wasmfs_rawfs` from that PR.

kleisauke added 2 commits April 2, 2026 20:27

Cherry-pick commit f3b85c9

11233e0

Merge branch 'main' into wasmfs-noderawfs-abspath

2dd31f5

tlively reviewed Apr 3, 2026

View reviewed changes

kleisauke added 2 commits April 3, 2026 10:43

Simplify

e21bc63

Fix NodeFS test failures after e21bc63

fa12429

kleisauke added a commit that referenced this pull request Apr 4, 2026

[WasmFS] Add missing dependency in the Node backend. NFC (#26596)

07d59b6

Split out from #24733.

		if (!root->getBackend()->isVirtualized()) {
		return {std::make_pair(std::move(curr), path)};

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