vfs: add remaining fs/promises VFS interceptions

Intercept the remaining ~18 fs methods that still called C++ bindings
directly when operating on VFS paths/FDs:

Path-based no-ops (VFS doesn't track permissions/ownership/timestamps):
- chown/chownSync, lchown/lchownSync, lutimes/lutimesSync

FD-based no-ops (VFS FDs don't need sync/permissions/ownership):
- fchmod/fchmodSync, fchown/fchownSync, futimes/futimesSync,
  fdatasync/fdatasyncSync, fsync/fsyncSync

Real implementations:
- statfs/statfsSync (return synthetic StatFs for VFS mount)
- readv/readvSync (scatter read via readSync loop)
- writev/writevSync (gather write via writeSync loop)

Promise API:
- lchmod, lchown, chown, lutimes, statfs

Also moves the VFS check in promises.lchmod() before the O_SYMLINK
gate so it works on Linux where O_SYMLINK is undefined.

Author: mcollina

lib/fs.js

@@ -876,12 +876,26 @@ function readv(fd, buffers, position, callback) {
   callback ||= position;
   validateFunction(callback, 'cb');
 
-  const req = new FSReqCallback();
-  req.oncomplete = wrapper;
-
   if (typeof position !== 'number')
     position = null;
 
+  const h = vfsState.handlers;
+  if (h !== null) {
+    try {
+      const result = h.readvSync(fd, buffers, position);
+      if (result !== undefined) {
+        process.nextTick(callback, null, result, buffers);
+        return;
+      }
+    } catch (err) {
+      process.nextTick(callback, err);
+      return;
+    }
+  }
+
+  const req = new FSReqCallback();
+  req.oncomplete = wrapper;
+
   binding.readBuffers(fd, buffers, position, req);
 }
 
@@ -903,6 +917,12 @@ function readvSync(fd, buffers, position) {
   if (typeof position !== 'number')
     position = null;
 
+  const h = vfsState.handlers;
+  if (h !== null) {
+    const result = h.readvSync(fd, buffers, position);
+    if (result !== undefined) return result;
+  }
+
   return binding.readBuffers(fd, buffers, position);
 }
 
@@ -1106,12 +1126,26 @@ function writev(fd, buffers, position, callback) {
     return;
   }
 
-  const req = new FSReqCallback();
-  req.oncomplete = wrapper;
-
   if (typeof position !== 'number')
     position = null;
 
+  const h = vfsState.handlers;
+  if (h !== null) {
+    try {
+      const result = h.writevSync(fd, buffers, position);
+      if (result !== undefined) {
+        process.nextTick(callback, null, result, buffers);
+        return;
+      }
+    } catch (err) {
+      process.nextTick(callback, err);
+      return;
+    }
+  }
+
+  const req = new FSReqCallback();
+  req.oncomplete = wrapper;
+
   binding.writeBuffers(fd, buffers, position, req);
 }
 
@@ -1139,6 +1173,12 @@ function writevSync(fd, buffers, position) {
   if (typeof position !== 'number')
     position = null;
 
+  const h = vfsState.handlers;
+  if (h !== null) {
+    const result = h.writevSync(fd, buffers, position);
+    if (result !== undefined) return result;
+  }
+
   return binding.writeBuffers(fd, buffers, position);
 }
 
@@ -1476,8 +1516,19 @@ function rmSync(path, options) {
  * @returns {void}
  */
 function fdatasync(fd, callback) {
+  callback = makeCallback(callback);
+
+  const h = vfsState.handlers;
+  if (h !== null) {
+    const result = h.fdatasyncSync(fd);
+    if (result !== undefined) {
+      process.nextTick(callback, null);
+      return;
+    }
+  }
+
   const req = new FSReqCallback();
-  req.oncomplete = makeCallback(callback);
+  req.oncomplete = callback;
 
   if (permission.isEnabled()) {
     callback(new ERR_ACCESS_DENIED('fdatasync API is disabled when Permission Model is enabled.'));
@@ -1494,6 +1545,12 @@ function fdatasync(fd, callback) {
  * @returns {void}
  */
 function fdatasyncSync(fd) {
+  const h = vfsState.handlers;
+  if (h !== null) {
+    const result = h.fdatasyncSync(fd);
+    if (result !== undefined) return;
+  }
+
   if (permission.isEnabled()) {
     throw new ERR_ACCESS_DENIED('fdatasync API is disabled when Permission Model is enabled.');
   }
@@ -1508,8 +1565,19 @@ function fdatasyncSync(fd) {
  * @returns {void}
  */
 function fsync(fd, callback) {
+  callback = makeCallback(callback);
+
+  const h = vfsState.handlers;
+  if (h !== null) {
+    const result = h.fsyncSync(fd);
+    if (result !== undefined) {
+      process.nextTick(callback, null);
+      return;
+    }
+  }
+
   const req = new FSReqCallback();
-  req.oncomplete = makeCallback(callback);
+  req.oncomplete = callback;
   if (permission.isEnabled()) {
     callback(new ERR_ACCESS_DENIED('fsync API is disabled when Permission Model is enabled.'));
     return;
@@ -1524,6 +1592,12 @@ function fsync(fd, callback) {
  * @returns {void}
  */
 function fsyncSync(fd) {
+  const h = vfsState.handlers;
+  if (h !== null) {
+    const result = h.fsyncSync(fd);
+    if (result !== undefined) return;
+  }
+
   if (permission.isEnabled()) {
     throw new ERR_ACCESS_DENIED('fsync API is disabled when Permission Model is enabled.');
   }
@@ -1992,6 +2066,16 @@ function statfs(path, options = { bigint: false }, callback) {
     options = kEmptyObject;
   }
   validateFunction(callback, 'cb');
+
+  const h = vfsState.handlers;
+  if (h !== null) {
+    const result = h.statfsSync(path);
+    if (result !== undefined) {
+      process.nextTick(callback, null, result);
+      return;
+    }
+  }
+
   path = getValidatedPath(path);
   const req = new FSReqCallback(options.bigint);
   req.oncomplete = (err, stats) => {
@@ -2087,6 +2171,12 @@ function statSync(path, options = { bigint: false, throwIfNoEntry: true }) {
 }
 
 function statfsSync(path, options = { bigint: false }) {
+  const h = vfsState.handlers;
+  if (h !== null) {
+    const result = h.statfsSync(path);
+    if (result !== undefined) return result;
+  }
+
   const stats = binding.statfs(getValidatedPath(path), options.bigint);
   return getStatFsFromBinding(stats);
 }
@@ -2376,6 +2466,15 @@ function fchmod(fd, mode, callback) {
   mode = parseFileMode(mode, 'mode');
   callback = makeCallback(callback);
 
+  const h = vfsState.handlers;
+  if (h !== null) {
+    const result = h.fchmodSync(fd);
+    if (result !== undefined) {
+      process.nextTick(callback, null);
+      return;
+    }
+  }
+
   if (permission.isEnabled()) {
     callback(new ERR_ACCESS_DENIED('fchmod API is disabled when Permission Model is enabled.'));
     return;
@@ -2393,6 +2492,12 @@ function fchmod(fd, mode, callback) {
  * @returns {void}
  */
 function fchmodSync(fd, mode) {
+  const h = vfsState.handlers;
+  if (h !== null) {
+    const result = h.fchmodSync(fd);
+    if (result !== undefined) return;
+  }
+
   if (permission.isEnabled()) {
     throw new ERR_ACCESS_DENIED('fchmod API is disabled when Permission Model is enabled.');
   }
@@ -2503,6 +2608,16 @@ function lchown(path, uid, gid, callback) {
   path = getValidatedPath(path);
   validateInteger(uid, 'uid', -1, kMaxUserId);
   validateInteger(gid, 'gid', -1, kMaxUserId);
+
+  const h = vfsState.handlers;
+  if (h !== null) {
+    const result = h.lchownSync(path);
+    if (result !== undefined) {
+      process.nextTick(callback, null);
+      return;
+    }
+  }
+
   const req = new FSReqCallback();
   req.oncomplete = callback;
   binding.lchown(path, uid, gid, req);
@@ -2519,6 +2634,13 @@ function lchownSync(path, uid, gid) {
   path = getValidatedPath(path);
   validateInteger(uid, 'uid', -1, kMaxUserId);
   validateInteger(gid, 'gid', -1, kMaxUserId);
+
+  const h = vfsState.handlers;
+  if (h !== null) {
+    const result = h.lchownSync(path);
+    if (result !== undefined) return;
+  }
+
   binding.lchown(path, uid, gid);
 }
 
@@ -2534,6 +2656,16 @@ function fchown(fd, uid, gid, callback) {
   validateInteger(uid, 'uid', -1, kMaxUserId);
   validateInteger(gid, 'gid', -1, kMaxUserId);
   callback = makeCallback(callback);
+
+  const h = vfsState.handlers;
+  if (h !== null) {
+    const result = h.fchownSync(fd);
+    if (result !== undefined) {
+      process.nextTick(callback, null);
+      return;
+    }
+  }
+
   if (permission.isEnabled()) {
     callback(new ERR_ACCESS_DENIED('fchown API is disabled when Permission Model is enabled.'));
     return;
@@ -2554,6 +2686,13 @@ function fchown(fd, uid, gid, callback) {
 function fchownSync(fd, uid, gid) {
   validateInteger(uid, 'uid', -1, kMaxUserId);
   validateInteger(gid, 'gid', -1, kMaxUserId);
+
+  const h = vfsState.handlers;
+  if (h !== null) {
+    const result = h.fchownSync(fd);
+    if (result !== undefined) return;
+  }
+
   if (permission.isEnabled()) {
     throw new ERR_ACCESS_DENIED('fchown API is disabled when Permission Model is enabled.');
   }
@@ -2576,6 +2715,15 @@ function chown(path, uid, gid, callback) {
   validateInteger(uid, 'uid', -1, kMaxUserId);
   validateInteger(gid, 'gid', -1, kMaxUserId);
 
+  const h = vfsState.handlers;
+  if (h !== null) {
+    const result = h.chownSync(path);
+    if (result !== undefined) {
+      process.nextTick(callback, null);
+      return;
+    }
+  }
+
   const req = new FSReqCallback();
   req.oncomplete = callback;
   binding.chown(path, uid, gid, req);
@@ -2593,6 +2741,13 @@ function chownSync(path, uid, gid) {
   path = getValidatedPath(path);
   validateInteger(uid, 'uid', -1, kMaxUserId);
   validateInteger(gid, 'gid', -1, kMaxUserId);
+
+  const h = vfsState.handlers;
+  if (h !== null) {
+    const result = h.chownSync(path);
+    if (result !== undefined) return;
+  }
+
   binding.chown(path, uid, gid);
 }
 
@@ -2666,6 +2821,15 @@ function futimes(fd, atime, mtime, callback) {
   mtime = toUnixTimestamp(mtime, 'mtime');
   callback = makeCallback(callback);
 
+  const h = vfsState.handlers;
+  if (h !== null) {
+    const result = h.futimesSync(fd);
+    if (result !== undefined) {
+      process.nextTick(callback, null);
+      return;
+    }
+  }
+
   if (permission.isEnabled()) {
     callback(new ERR_ACCESS_DENIED('futimes API is disabled when Permission Model is enabled.'));
     return;
@@ -2686,6 +2850,12 @@ function futimes(fd, atime, mtime, callback) {
  * @returns {void}
  */
 function futimesSync(fd, atime, mtime) {
+  const h = vfsState.handlers;
+  if (h !== null) {
+    const result = h.futimesSync(fd);
+    if (result !== undefined) return;
+  }
+
   if (permission.isEnabled()) {
     throw new ERR_ACCESS_DENIED('futimes API is disabled when Permission Model is enabled.');
   }
@@ -2710,6 +2880,15 @@ function lutimes(path, atime, mtime, callback) {
   callback = makeCallback(callback);
   path = getValidatedPath(path);
 
+  const h = vfsState.handlers;
+  if (h !== null) {
+    const result = h.lutimesSync(path);
+    if (result !== undefined) {
+      process.nextTick(callback, null);
+      return;
+    }
+  }
+
   const req = new FSReqCallback();
   req.oncomplete = callback;
   binding.lutimes(
@@ -2729,8 +2908,16 @@ function lutimes(path, atime, mtime, callback) {
  * @returns {void}
  */
 function lutimesSync(path, atime, mtime) {
+  path = getValidatedPath(path);
+
+  const h = vfsState.handlers;
+  if (h !== null) {
+    const result = h.lutimesSync(path);
+    if (result !== undefined) return;
+  }
+
   binding.lutimes(
-    getValidatedPath(path),
+    path,
     toUnixTimestamp(atime),
     toUnixTimestamp(mtime),
   );