IRC, freenode, #hurd, 2011-10-31:

<pinotree> is there some example of translator replying to custom ioctl's?
<pinotree> let's say you define some ioctl (those which can be represented)
  using the _IOW etc macros; how would a translator (or something else)
  "register" and reply to them?
<youpi> it's not an easy thing
<youpi> see hurd/hurd/tioctl.defs for instance
<youpi> that's where the 't' ioctls end up
<youpi> ('t' being the group in the _IOW macro)
<braunr> it's not that hard either
<pinotree> youpi: so you "roll" the ioctl to an ipc call with proper
<braunr> yes
<pinotree> ah ok, i thought there was some way to hook new ioctl's, and
  have libc send the whole stuff at once
<braunr> and the proper number (with a clear name)
<braunr> hm
<braunr> for many ioctls, you don't have to change libc
<youpi> yes, there's a script which produces the .defs from _IOW calls,
<youpi> or something like this
<youpi> there's also a hook thing in glibc, but for "sane" ioctls, that's
  not needed
<youpi> (_hurd_lookup_ioctl_handler called by ioctl())
<youpi> yes, see the rules in hurd/hurd/Makefile
<youpi> "The following rules assist in creating an `Xioctl.defs' file  to
  define RPCs that are sent primarily by ioctl commands."
<antrik> well, you can have perfectly sane ioctl()s that still can't be
  expressed within the constraints of the IO* macros... but admittedly
  that's rather uncommon
<antrik> (unless you consider passing of structs generally insane...)
<youpi> I didn't want to spend time on finding an appropriate adjective
  instaed of "sane"
<youpi> while I knew he would understand what I meant (and you did)
<youpi> (though  maybe not actually)
<youpi> by "sane", I mean, which use _IOW properly
<youpi> i.e. with a group, proper numbers, etc.
<youpi> (the imposed contraints on the parameters is obviously a flaw in
  the hurdish ioctl design, and not insanity from structures)