Implement fstatat flag: AT_EMPTY_PATH

src/library_syscall.js

@@ -25,20 +25,26 @@ var SyscallsLibrary = {
     umask: 0x1FF,  // S_IRWXU | S_IRWXG | S_IRWXO
 
     // shared utilities
-    calculateAt: function(dirfd, path) {
-      if (path[0] !== '/') {
-        // relative path
-        var dir;
-        if (dirfd === {{{ cDefine('AT_FDCWD') }}}) {
-          dir = FS.cwd();
-        } else {
-          var dirstream = FS.getStream(dirfd);
-          if (!dirstream) throw new FS.ErrnoError({{{ cDefine('EBADF') }}});
-          dir = dirstream.path;
+    calculateAt: function(dirfd, path, allowEmpty) {
+      if (path[0] === '/') {
+        return path;
+      }
+      // relative path
+      var dir;
+      if (dirfd === {{{ cDefine('AT_FDCWD') }}}) {
+        dir = FS.cwd();
+      } else {
+        var dirstream = FS.getStream(dirfd);
+        if (!dirstream) throw new FS.ErrnoError({{{ cDefine('EBADF') }}});
+        dir = dirstream.path;
+      }
+      if (path.length == 0) {
+        if (!allowEmpty) {
+          throw new FS.ErrnoError({{{ cDefine('ENOENT') }}});;
         }
-        path = PATH.join2(dir, path);
+        return dir;
       }
-      return path;
+      return PATH.join2(dir, path);
     },
 
     doStat: function(func, path, buf) {
@@ -1273,11 +1279,12 @@ var SyscallsLibrary = {
   __sys_fstatat64: function(dirfd, path, buf, flags) {
     path = SYSCALLS.getStr(path);
     var nofollow = flags & {{{ cDefine('AT_SYMLINK_NOFOLLOW') }}};
-    flags = flags & (~{{{ cDefine('AT_SYMLINK_NOFOLLOW') }}});
+    var allowEmpty = flags & {{{ cDefine('AT_EMPTY_PATH') }}};
+    flags = flags & (~{{{ cDefine('AT_SYMLINK_NOFOLLOW') | cDefine('AT_EMPTY_PATH') }}});
 #if ASSERTIONS
     assert(!flags, flags);
 #endif
-    path = SYSCALLS.calculateAt(dirfd, path);
+    path = SYSCALLS.calculateAt(dirfd, path, allowEmpty);
     return SYSCALLS.doStat(nofollow ? FS.lstat : FS.stat, path, buf);
   },
   __sys_unlinkat: function(dirfd, path, flags) {

src/struct_info.json

@@ -131,7 +131,8 @@
             "O_WRONLY",
             "AT_FDCWD",
             "AT_SYMLINK_NOFOLLOW",
-            "AT_REMOVEDIR"
+            "AT_REMOVEDIR",
+            "AT_EMPTY_PATH"
         ],
         "structs": {
             "flock": [

tests/stat/test_fstatat.c

@@ -0,0 +1,146 @@
+/*
+ * Copyright 2021 The Emscripten Authors.  All rights reserved.
+ * Emscripten is available under two separate licenses, the MIT license and the
+ * University of Illinois/NCSA Open Source License.  Both these licenses can be
+ * found in the LICENSE file.
+ */
+
+#include <assert.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+#include <unistd.h>
+#include <sys/stat.h>
+
+
+void create_file(const char *path, const char *buffer, int mode) {
+  int fd = open(path, O_WRONLY | O_CREAT | O_EXCL, mode);
+  assert(fd >= 0);
+
+  int err = write(fd, buffer, sizeof(char) * strlen(buffer));
+  assert(err ==  (sizeof(char) * strlen(buffer)));
+
+  close(fd);
+}
+
+void setup() {
+  mkdir("folder", 0777);
+  create_file("folder/file", "abcdef", 0777);
+  symlink("file", "folder/file-link");
+}
+
+void test() {
+  int err;
+  struct stat s;
+
+  int fd = open(".", O_RDONLY);
+  assert(fd >= 0);
+
+  // missing file
+  err = fstatat(fd, "does_not_exist", &s, 0);
+  assert(err == -1);
+  printf("errno: %d\n", errno);
+  assert(errno == ENOENT);
+
+  // stat a folder
+  memset(&s, 0, sizeof(s));
+  err = fstatat(fd, "folder", &s, 0);
+  assert(!err);
+  assert(s.st_dev);
+  assert(s.st_ino);
+  assert(S_ISDIR(s.st_mode));
+  assert(s.st_nlink);
+  assert(s.st_rdev == 0);
+  assert(s.st_size);
+  assert(s.st_ctime);
+#ifdef __EMSCRIPTEN__
+  assert(s.st_blksize == 4096);
+  assert(s.st_blocks == 1);
+#endif
+
+  // stat a file
+  memset(&s, 0, sizeof(s));
+  err = fstatat(fd, "folder/file", &s, 0);
+  assert(!err);
+  assert(s.st_dev);
+  assert(s.st_ino);
+  assert(S_ISREG(s.st_mode));
+  assert(s.st_nlink);
+  assert(s.st_rdev == 0);
+  assert(s.st_size == 6);
+  assert(s.st_ctime);
+#ifdef __EMSCRIPTEN__
+  assert(s.st_blksize == 4096);
+  assert(s.st_blocks == 1);
+#endif
+
+  close(fd);
+
+  fd = open("folder", O_RDONLY);
+  assert(fd >= 0);
+
+  // missing file
+  err = fstatat(fd, "does_not_exist", &s, 0);
+  assert(err == -1);
+  assert(errno == ENOENT);
+
+  // stat a file
+  memset(&s, 0, sizeof(s));
+  err = fstatat(fd, "file", &s, 0);
+  assert(!err);
+
+  // empty path - not allowed
+  err = fstatat(fd, "", &s, 0);
+  assert(err == -1);
+  assert(errno == ENOENT);
+
+  // empty path - with AT_EMPTY_PATH (stat's the fd itself, a directory in this case)
+  memset(&s, 0, sizeof(s));
+  err = fstatat(fd, "", &s, AT_EMPTY_PATH);
+  assert(!err);
+  assert(s.st_dev);
+  assert(s.st_ino);
+  assert(S_ISDIR(s.st_mode));
+  assert(s.st_nlink);
+  assert(s.st_rdev == 0);
+  assert(s.st_size);
+  assert(s.st_ctime);
+#ifdef __EMSCRIPTEN__
+  assert(s.st_blksize == 4096);
+  assert(s.st_blocks == 1);
+#endif
+
+  close(fd);
+
+  fd = open("folder/file", O_RDONLY);
+  assert(fd >= 0);
+
+  // empty path - with AT_EMPTY_PATH (stat's the fd itself, a file)
+  memset(&s, 0, sizeof(s));
+  err = fstatat(fd, "", &s, AT_EMPTY_PATH);
+  assert(!err);
+  assert(s.st_dev);
+  assert(s.st_ino);
+  assert(S_ISREG(s.st_mode));
+  assert(s.st_nlink);
+  assert(s.st_rdev == 0);
+  assert(s.st_size == 6);
+  assert(s.st_ctime);
+#ifdef __EMSCRIPTEN__
+  assert(s.st_blksize == 4096);
+  assert(s.st_blocks == 1);
+#endif
+
+  close(fd);
+
+  puts("success");
+}
+
+int main() {
+  setup();
+  test();
+  return 0;
+}

tests/stat/test_stat.c

@@ -32,7 +32,7 @@ void create_file(const char *path, const char *buffer, int mode) {
 
 void setup() {
   struct utimbuf t = {1200000000, 1200000000};
-  
+
   mkdir("folder", 0777);
   create_file("folder/file", "abcdef", 0777);
   symlink("file", "folder/file-link");
@@ -53,6 +53,11 @@ void test() {
   struct stat s;
   struct utimbuf t = {1200000000, 1200000000};
 
+  // non-existent
+  err = stat("does_not_exist", &s);
+  assert(err == -1);
+  assert(errno == ENOENT);
+
   // stat a folder
   memset(&s, 0, sizeof(s));
   err = stat("folder", &s);

tests/test_core.py

@@ -4949,6 +4949,9 @@ def test_stat(self):
     self.do_runf(path_from_root('tests', 'stat', 'test_stat.c'), 'success')
     self.verify_in_strict_mode('test_stat.js')
 
+  def test_fstatat(self):
+    self.do_runf(path_from_root('tests', 'stat', 'test_fstatat.c'), 'success')
+
   def test_stat_chmod(self):
     self.do_runf(path_from_root('tests', 'stat', 'test_chmod.c'), 'success')
 

tests/test_other.py

@@ -3762,15 +3762,15 @@ def test_stat_silly(self):
     const char *path = argv[i];
     struct stat path_stat;
     if (stat(path, &path_stat) != 0) {
-      printf("Failed to stat path: %s; errno=%d\n", path, errno);
+      printf("Failed to stat path: '%s'; errno=%d\n", path, errno);
     } else {
-      printf("ok on %s\n", path);
+      printf("stat success on '%s'\n", path);
     }
   }
 }
     ''')
-    self.do_runf('src.cpp', r'''Failed to stat path: /a; errno=44
-Failed to stat path: ; errno=44
+    self.do_runf('src.cpp', r'''Failed to stat path: '/a'; errno=44
+Failed to stat path: ''; errno=44
 ''', args=['/a', ''])
 
   def test_symlink_silly(self):