Using extended attributes of the file system in ceph

In the filestore in ceph, there is a key-value that implements cascade in chain_xattr.cc. Of course, the xattr here is saved in the file system
in extended properties.
The so-called cascade means that a key can correspond to a fragment of multiple values
For example key@1 and key@2 are parsed as key-12 by chain_xattr
Ceph mainly uses the user command space of xattr
The user namespace in xattr used by ceph can be seen from the code below

static void get_attrname(const char *name, char *buf, int len)
{
  snprintf(buf, len, "user.ceph.%s", name);
}

bool parse_attrname(char **name)
{
  if (strncmp(*name, "user.ceph.", 10) == 0) {
    *name += 10;
    return true;
  }
  return false;
}
Why use @ as separator between key and value? As can be seen from the code below
void get_raw_xattr_name(const char *name, int i, char *raw_name, int raw_len)
{
  int pos = 0;

  while (*name) {
    switch (*name) {
    case '@': /* escape it */
      pos += 2;
      assert (pos < raw_len - 1);
      *raw_name = '@';
      raw_name++;
      *raw_name = '@';
      break;
    default:
      pos++;
      assert(pos < raw_len - 1);
      *raw_name = *name;
      break;
    }
    name++;
    raw_name++;
  }

  if (!i) {
    *raw_name = '\0';
  } else {
  #From here you can know that @ is used as a separator between key and value
    int r = snprintf(raw_name, raw_len - pos, "@%d", i);
    assert(r < raw_len - pos);
  }
}