Function __syscall_unlinkat

system/lib/wasmfs/syscalls.cpp:813–870

TODO: Test this with non-AT_FDCWD values.

// TODO: Test this with non-AT_FDCWD values.
int __syscall_unlinkat(int dirfd, const char* path, int flags) {
  if (flags & ~AT_REMOVEDIR) {
    // TODO: Test this case.
    return -EINVAL;
  }
  // It is invalid for rmdir paths to end in ".", but we need to distinguish
  // this case from the case of `parseParent` returning (root, '.') when parsing
  // "/", so we need to find the invalid "/." manually.
  if (flags == AT_REMOVEDIR) {
    std::string_view p(path);
    // Ignore trailing '/'.
    while (!p.empty() && p.back() == '/') {
      p.remove_suffix(1);
    }
    if (p.size() >= 2 && p.substr(p.size() - 2) == std::string_view("/.")) {
      return -EINVAL;
    }
  }
  auto parsed = path::parseParent(path, dirfd);
  if (auto err = parsed.getError()) {
    return err;
  }
  auto& [parent, childNameView] = parsed.getParentChild();
  std::string childName(childNameView);
  auto lockedParent = parent->locked();
  auto file = lockedParent.getChild(childName);
  if (!file) {
    return -ENOENT;
  }
  // Disallow removing the root directory, even if it is empty.
  if (file == wasmFS.getRootDirectory()) {
    return -EBUSY;
  }

  auto lockedFile = file->locked();
  if (auto dir = file->dynCast<Directory>()) {
    if (flags != AT_REMOVEDIR) {
      return -EISDIR;
    }
    // A directory can only be removed if it has no entries.
    if (dir->locked().getNumEntries() > 0) {
      return -ENOTEMPTY;
    }
  } else {
    // A normal file or symlink.
    if (flags == AT_REMOVEDIR) {
      return -ENOTDIR;
    }
  }

  // Cannot unlink/rmdir if the parent dir doesn't have write permissions.
  if (!(lockedParent.getMode() & WASMFS_PERM_WRITE)) {
    return -EACCES;
  }

  // Input is valid, perform the unlink.
  return lockedParent.removeChild(childName);
}