[WasmFS] Fix absolute path access under NODERAWFS

Resolves: #24830.
Resolves: #24836.

Author: kleisauke

src/lib/libwasmfs_node.js

@@ -206,7 +206,7 @@ addToLibrary({
     return wasmfsTry(() => {
       // TODO: Cache open file descriptors to guarantee that opened files will
       // still exist when we try to access them.
-      let nread = fs.readSync(fd, new Int8Array(HEAPU8.buffer, buf_p, len), 0, len, pos);
+      let nread = fs.readSync(fd, HEAPU8.subarray(buf_p, buf_p + len), 0, len, pos);
       {{{ makeSetValue('nread_p', 0, 'nread', 'i32') }}};
       // implicitly return 0
     });
@@ -217,7 +217,7 @@ addToLibrary({
     return wasmfsTry(() => {
       // TODO: Cache open file descriptors to guarantee that opened files will
       // still exist when we try to access them.
-      let nwritten = fs.writeSync(fd, new Int8Array(HEAPU8.buffer, buf_p, len), 0, len, pos);
+      let nwritten = fs.writeSync(fd, HEAPU8.subarray(buf_p, buf_p + len), 0, len, pos);
       {{{ makeSetValue('nwritten_p', 0, 'nwritten', 'i32') }}};
       // implicitly return 0
     });

system/include/emscripten/wasmfs.h

@@ -77,7 +77,7 @@ backend_t wasmfs_create_memory_backend(void);
 //
 backend_t wasmfs_create_fetch_backend(const char* _Nonnull base_url, uint32_t chunk_size);
 
-backend_t wasmfs_create_node_backend(const char* _Nonnull root);
+backend_t wasmfs_create_node_backend(const char* _Nonnull mount_path);
 
 // Note: this cannot be called on the browser main thread because it might
 // deadlock while waiting for the OPFS dedicated worker thread to be spawned.
@@ -111,6 +111,11 @@ void wasmfs_flush(void);
 // default backend is used.
 backend_t wasmfs_create_root_dir(void);
 
+// A hook users can do to create the working directory. Overriding this allows
+// the user to set a particular backend as the CWD. If this is not set then the
+// result of wasmfs_create_root_dir() is used.
+backend_t wasmfs_create_working_dir(void);
+
 // A hook users can do to run code during WasmFS startup. This hook happens
 // before file preloading, so user code could create backends and mount them,
 // which would then affect in which backend the preloaded files are loaded (the

system/lib/wasmfs/backends/node_backend.cpp

@@ -191,7 +191,9 @@ class NodeDirectory : public Directory {
     if (_wasmfs_node_get_mode(childPath.c_str(), &mode)) {
       return nullptr;
     }
-    if (S_ISREG(mode)) {
+    // Allow reading from character device files (e.g. `/dev/random`,
+    // `/dev/urandom`)
+    if (S_ISREG(mode) || S_ISCHR(mode)) {
       return std::make_shared<NodeFile>(mode, getBackend(), childPath);
     } else if (S_ISDIR(mode)) {
       return std::make_shared<NodeDirectory>(mode, getBackend(), childPath);
@@ -300,8 +302,8 @@ class NodeBackend : public Backend {
 
 extern "C" {
 
-backend_t wasmfs_create_node_backend(const char* root) {
-  return wasmFS.addBackend(std::make_unique<NodeBackend>(root));
+backend_t wasmfs_create_node_backend(const char* mount_path) {
+  return wasmFS.addBackend(std::make_unique<NodeBackend>(mount_path));
 }
 
 void EMSCRIPTEN_KEEPALIVE _wasmfs_node_record_dirent(

system/lib/wasmfs/backends/noderawfs_root.cpp

@@ -5,6 +5,10 @@
 
 #include "emscripten/wasmfs.h"
 
-backend_t wasmfs_create_root_dir(void) {
+backend_t wasmfs_create_root_dir() {
+  return wasmfs_create_node_backend("");
+}
+
+backend_t wasmfs_create_working_dir() {
   return wasmfs_create_node_backend(".");
 }

system/lib/wasmfs/wasmfs.cpp

@@ -37,7 +37,7 @@ __attribute__((init_priority(100))) WasmFS wasmFS;
 __attribute__((weak)) extern "C" void wasmfs_before_preload(void) {}
 
 // Set up global data structures and preload files.
-WasmFS::WasmFS() : rootDirectory(initRootDirectory()), cwd(rootDirectory) {
+WasmFS::WasmFS() : rootDirectory(initRootDirectory()), cwd(initCWD()) {
   wasmfs_before_preload();
   preloadFiles();
 }
@@ -87,8 +87,8 @@ WasmFS::~WasmFS() {
   rootDirectory->locked().setParent(nullptr);
 }
 
-// Special backends that want to install themselves as the root use this hook.
-// Otherwise, we use the default backends.
+// Hooks for backends that want to install themselves as the root or CWD.
+// Otherwise, we use the default memory backends.
 __attribute__((weak)) extern "C" backend_t wasmfs_create_root_dir(void) {
 #ifdef WASMFS_CASE_INSENSITIVE
   return createIgnoreCaseBackend([]() { return createMemoryBackend(); });
@@ -97,6 +97,8 @@ __attribute__((weak)) extern "C" backend_t wasmfs_create_root_dir(void) {
 #endif
 }
 
+__attribute__((weak)) extern "C" backend_t wasmfs_create_working_dir(void);
+
 std::shared_ptr<Directory> WasmFS::initRootDirectory() {
   auto rootBackend = wasmfs_create_root_dir();
   auto rootDirectory =
@@ -126,6 +128,21 @@ std::shared_ptr<Directory> WasmFS::initRootDirectory() {
   return rootDirectory;
 }
 
+std::shared_ptr<Directory> WasmFS::initCWD() {
+  if (wasmfs_create_working_dir == nullptr) {
+    return rootDirectory;
+  }
+
+  auto cwdBackend = wasmfs_create_working_dir();
+  auto cwd = cwdBackend->createDirectory(S_IRUGO | S_IXUGO | S_IWUGO);
+  auto lockedCwd = cwd->locked();
+
+  // The current working directory is its own parent.
+  lockedCwd.setParent(cwd);
+
+  return cwd;
+}
+
 // Initialize files specified by the --preload-file option.
 // Set up directories and files in wasmFS$preloadedDirs and
 // wasmFS$preloadedFiles from JS. This function will be called before any file

system/lib/wasmfs/wasmfs.h

@@ -32,6 +32,9 @@ class WasmFS {
   // dev/stderr. Refers to the same std streams in the open file table.
   std::shared_ptr<Directory> initRootDirectory();
 
+  // Private method to initialize CWD once.
+  std::shared_ptr<Directory> initCWD();
+
   // Initialize files specified by --preload-file option.
   void preloadFiles();
 

test/fs/test_fs_dev_random.c

@@ -13,12 +13,14 @@ int main() {
   int nread;
 
   fp = fopen("/dev/random", "r");
-  nread = fread(&data, 1, byte_count, fp);
+  assert(fp != NULL);
+  nread = fread(data, 1, byte_count, fp);
   assert(nread == byte_count);
   fclose(fp);
 
   fp = fopen("/dev/urandom", "r");
-  nread = fread(&data, 1, byte_count, fp);
+  assert(fp != NULL);
+  nread = fread(data, 1, byte_count, fp);
   assert(nread == byte_count);
   fclose(fp);
 

test/test_other.py

@@ -9255,16 +9255,43 @@ 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')])
 
+  @crossplatform
+  @also_with_wasmfs
+  def test_noderawfs_open_abspath(self):
+    create_file('foo', 'bar')
+    create_file('open.c', r'''
+      #include <stdio.h>
+      #include <fcntl.h>
+      #include <assert.h>
+      #include <unistd.h>
+      int main(int argc, char** argv) {
+        printf("testing open to %s\n", argv[1]);
+        int fd = open(argv[1], O_RDONLY, 0644);
+        assert(fd >= 0);
+        int rtn = close(fd);
+        assert(rtn == 0);
+        return 0;
+      }
+    ''')
+    self.do_runf('open.c', cflags=['-sNODERAWFS'], args=[os.path.abspath('foo')])
+
   def test_noderawfs_readfile_prerun(self):
     create_file('foo', 'bar')
     self.add_pre_run("console.log(FS.readFile('foo', { encoding: 'utf8' }));")
@@ -13210,11 +13237,10 @@ def test_unistd_chown(self):
     self.set_setting('WASMFS')
     self.do_run_in_out_file_test('wasmfs/wasmfs_chown.c')
 
-  @wasmfs_all_backends
   def test_wasmfs_getdents(self):
     # Run only in WASMFS for now.
     self.set_setting('FORCE_FILESYSTEM')
-    self.do_run_in_out_file_test('wasmfs/wasmfs_getdents.c')
+    self.do_run_in_out_file_test('wasmfs/wasmfs_getdents.c', cflags=['-sWASMFS'])
 
   def test_wasmfs_jsfile(self):
     self.set_setting('WASMFS')
@@ -13801,15 +13827,11 @@ 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')
     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):