[WasmFS] Fix absolute path access under NODERAWFS

system/lib/wasmfs/backend.h

@@ -21,6 +21,11 @@ class Backend {
   virtual std::shared_ptr<Directory> createDirectory(mode_t mode) = 0;
   virtual std::shared_ptr<Symlink> createSymlink(std::string target) = 0;
 
+  // Returns true if this backend requires WasmFS to traverse and resolve
+  // paths (e.g. because it is mounted under a prefix). Returns false if
+  // paths can be passed through directly to the backend.
+  virtual bool requiresPathTraversal() { return true; }
+
   virtual ~Backend() = default;
 };
 

system/lib/wasmfs/backends/node_backend.cpp

@@ -23,6 +23,9 @@ class NodeState {
   int fd = -1;
 
 public:
+  // Base path in the host filesystem for this backend.
+  // An empty string means "no base path": paths are used as-is without
+  // prefixing.
   std::string path;
 
   NodeState(std::string path) : path(path) {}
@@ -180,6 +183,11 @@ class NodeDirectory : public Directory {
 
 private:
   std::string getChildPath(const std::string& name) {
+    // If state.path is empty, this backend represents the real root and paths
+    // should be passed through unchanged.
+    if (state.path.empty()) {
+      return name;
+    }
     return state.path + '/' + name;
   }
 
@@ -296,6 +304,10 @@ class NodeBackend : public Backend {
   std::shared_ptr<Symlink> createSymlink(std::string target) override {
     WASMFS_UNREACHABLE("TODO: implement NodeBackend::createSymlink");
   }
+
+  virtual bool requiresPathTraversal() override {
+    return !mountPath.empty();
+  }
 };
 
 // TODO: symlink

system/lib/wasmfs/backends/noderawfs_root.cpp

@@ -6,5 +6,9 @@
 #include "emscripten/wasmfs.h"
 
 backend_t wasmfs_create_root_dir(void) {
-  return wasmfs_create_node_backend(".");
+  // Use an empty string as the backend "path" to indicate that this backend
+  // is mounted at the real filesystem root. In this mode, paths are passed
+  // through verbatim (no "./" prefix or path rewriting), which is required
+  // for correct handling of absolute paths under NODERAWFS.
+  return wasmfs_create_node_backend("");
 }

system/lib/wasmfs/paths.cpp

@@ -66,12 +66,21 @@ ParsedParent doParseParent(std::string_view path,
                            size_t& recursions) {
   // Empty paths never exist.
   if (path.empty()) {
-    return {-ENOENT};
+    return -ENOENT;
+  }
+
+  auto root = wasmFS.getRootDirectory();
+
+  // If the root backend does not require path traversal, it can operate on the
+  // 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)};
   }
 
   // Handle absolute paths.
   if (path.front() == '/') {
-    curr = wasmFS.getRootDirectory();
+    curr = root;
     path.remove_prefix(1);
   }
 
@@ -84,7 +93,7 @@ ParsedParent doParseParent(std::string_view path,
   // contain a child segment for us to return. The root is its own parent, so we
   // can handle this by returning (root, ".").
   if (path.empty()) {
-    return {std::make_pair(std::move(curr), std::string_view("."))};
+    return {std::make_pair(std::move(curr), ".")};
   }
 
   while (true) {

test/test_core.py

@@ -6151,9 +6151,12 @@ def test_unistd_unlink(self):
 
     # Several differences/bugs on non-linux including https://github.com/nodejs/node/issues/18014
     # TODO: NODERAWFS in WasmFS
-    if '-DNODERAWFS' in self.cflags and os.geteuid() == 0:
+    if '-DNODERAWFS' in self.cflags:
       # 0 if root user
-      self.cflags += ['-DSKIP_ACCESS_TESTS']
+      if os.geteuid() == 0:
+        self.cflags += ['-DSKIP_ACCESS_TESTS']
+      if self.get_setting('WASMFS'):
+        self.skipTest('https://github.com/emscripten-core/emscripten/issues/18112')
 
     self.do_runf('unistd/unlink.c', 'success')
 

test/test_other.py

@@ -9291,12 +9291,19 @@ def test_noderawfs_disables_embedding(self):
     self.assert_fail(base + ['--preload-file', 'somefile'], expected)
     self.assert_fail(base + ['--embed-file', 'somefile'], expected)
 
+  @crossplatform
+  @also_with_wasmfs
   def test_noderawfs_access_abspath(self):
     create_file('foo', 'bar')
     create_file('access.c', r'''
+      #include <stdio.h>
+      #include <assert.h>
       #include <unistd.h>
       int main(int argc, char** argv) {
-        return access(argv[1], F_OK);
+        printf("testing access to %s\n", argv[1]);
+        int rtn = access(argv[1], F_OK);
+        assert(rtn == 0);
+        return 0;
       }
     ''')
     self.do_runf('access.c', cflags=['-sNODERAWFS'], args=[os.path.abspath('foo')])
@@ -13256,6 +13263,8 @@ def test_unistd_chown(self):
 
   @wasmfs_all_backends
   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')
@@ -13844,15 +13853,13 @@ def test_fs_icase(self):
   @crossplatform
   @with_all_fs
   def test_std_filesystem(self):
-    if self.get_setting('NODERAWFS') and self.get_setting('WASMFS'):
-      self.skipTest('https://github.com/emscripten-core/emscripten/issues/24830')
+    if (WINDOWS or MACOS) and self.get_setting('NODERAWFS') and self.get_setting('WASMFS'):
+      self.skipTest('fails with ENOTEMPTY (Directory not empty) during fs::remove_all')
     self.do_other_test('test_std_filesystem.cpp')
 
   @crossplatform
   @with_all_fs
   def test_std_filesystem_tempdir(self):
-    if self.get_setting('NODERAWFS') and self.get_setting('WASMFS'):
-      self.skipTest('https://github.com/emscripten-core/emscripten/issues/24830')
     self.do_other_test('test_std_filesystem_tempdir.cpp', cflags=['-g'])
 
   def test_strict_js_closure(self):