fs.access throws permission error while checking W_OK on writable dir

• Version: v10.16.0 (also happening on v12.6.0)
• Platform: 18.6.0 Darwin Kernel Version 18.6.0 (also happening on 4.15.0-54-generic Ubuntu)
• Subsystem: fs

I'm experiencing a rather unexpected behaviour when trying fs.access on a directory that's also an NFS shared mount point. The check for fs.constants.W_OK throws Error: EACCES: permission denied, access '/mnt/test/nfs' even though the directory is writable and permissions seem to be correct for the user running the node script process.

Below is a reproduction of what I'm seeing.

const os = require('os');
const path = require('path');
const fs = require('fs');

// Path to the mount directory
const MOUNT_PATH = '/mnt/test/nfs';

const filePath = path.join(MOUNT_PATH, 'foo.txt');

// Write a file
fs.writeFileSync(filePath, 'Hello world!'); // Passes OK

// Read a file
const contents = fs.readFileSync(filePath); // Passes OK
console.log(contents.toString('utf-8')); // 'Hello World!'

// Get stats
os.userInfo();
/*
{
  uid: 431,
  gid: 433,
  username: 'test',
  homedir: '/home/test',
  shell: '/sbin/nologin'
}
*/

fs.stat(MOUNT_PATH, console.log);
/*
> null Stats {
  dev: 52,
  mode: 16895, <- '0777' octal
  nlink: 1,
  uid: 431, <- Correct uid
  gid: 433, <- Correct gid
  rdev: 0,
  blksize: 4096,
  ino: 263,
  size: 184,
  blocks: 0,
  atimeMs: 1562948571578.2288,
  mtimeMs: 1562897414354.1873,
  ctimeMs: 1562897414354.1873,
  birthtimeMs: 0,
  atime: 2019-07-12T16:22:51.578Z,
  mtime: 2019-07-12T02:10:14.354Z,
  ctime: 2019-07-12T02:10:14.354Z,
  birthtime: 1970-01-01T00:00:00.000Z
}
*/


// Test permissions
fs.access(MOUNT_PATH, fs.constants.R_OK, console.error); // Passes OK
fs.access(MOUNT_PATH, fs.constants.W_OK, console.error); 
/* 
 [Error: EACCES: permission denied, access '/mnt/test/nfs'] {
  errno: -13,
  code: 'EACCES',
  syscall: 'access',
  path: '/mnt/test/nfs'
*/

This does not happen on any other directory outside the NFS share. I stumbled upon the exception when writing a very simple health checker script to test the mount availability for a running web service.

Am I missing something? What's the catch here? Thanks in advance.

首先在报告的 NFS 挂载上使用 fs.access(MOUNT_PATH, fs.constants.W_OK) 进行复现，并将其与 fs.writeFileSync、fs.readFileSync、fs.stat 和 R_OK 检查进行比较。确定不同的结果是预期的 NFS 行为，还是 Node.js 处理 fs.access 时存在问题；完成标准是记录原因，或确定一项有针对性的 runtime 更改及其验证方式。