IRC, freenode, #hurd, 2011-11-12:

<sea4ever> So hurd implements a 'transparent translator' somewhere which
  just passes all IO calls to the posix IO I'm used to? (i.e. read, write,
  open, close, etc.?)
<youpi> it's the normal way of operation
<youpi> glibc's read() doesn't do a system call, it always does an RPC to
  the underlying translator
<youpi> be it ext2fs for /, or your foobarfs for your node
<sea4ever> Ok that makes sense. How does one program know which translator
  it should refer to though?
<sea4ever> the read() call magically knows which process to invoke?
<youpi> the / translator is always known
<youpi> and then you ask /'s translator about /home, then /home/you, then
<youpi> it tells you which other translator tyou have to contact
<youpi> that's on open
<sea4ever> It's a tree! Ok.
<youpi> the notion of fd is then simply knowing the translator
<sea4ever> Right. 'file descriptor' is now 'translator address descriptor'
<youpi> it's glibc which knows about FDs, nothing else knows
<youpi> yes
<youpi> actually an RPC port, simply
<sea4ever> I want to try out the new RPC mechanism that mach implements
<youpi> err, which "new" RPC ?
<youpi> mach's RPCs are very old actually :)