IRC, freenode, #hurd, 2011-10-18:

<pinotree> i guess it is not normal for /dev/zero have a size of
  (size_t)-1, no?
<pinotree> (it isn't (size_t)-1, but (long long)-1)

2011-10-19:

<pinotree> see the size you get with `stat /dev/zero`