[EROS-Arch] Installers

[Kragen Sitaker]

Seth Arnold asks:
> However, would install programs/scripts on EROS get away with doing
> less? Might the installers have to do *more*, just to get around the OS
> doing less? IE, it might need to make a 'filesystem' for itself (ftp
> server?), cook a partition for database use, handle interrupts in
> strange devices, ... I just don't know what is desired/expected/possible
> for the installer programs, mainly because I am unfamiliar with them.

Making a filesystem for oneself is simple --- you need access to the
factory that makes filesystems (normally granted to most programs,
since that factory doesn't convey any authority) and enough space from
the space bank to create the filesystem.

"Cooking a partition" presumably means constructing some proxy object
for some bunch of space.  Again, if you have access to the space, you
can do this with no special privs.

The authority to handle interrupts in strange devices probably also
implies the authority to handle interrupts in non-strange devices and
to send to random I/O ports, which probably conveys the authority to
overwrite random chunks of RAM.  So this authority is equivalent to
complete control over the system.

If you're on a system like an S/390 which has a sane enough I/O system
that this isn't true, you can hand the authority for that particular
device to the installer.

I think installers should be Turing-complete --- after all, the
software they're installing is, and presumably you're going to run that
software eventually, or you wouldn't install it, and presumably the
person who created the installer also has control over the installed
program --- but they rarely need to be Turing-complete programs with
complete control over your system.

The authorities the installer needs should be declared, not computed;
they are, in some sense, the equivalent of the undefined external
symbols in an object file.  But the installer itself should be
Turing-complete.

-- 
<kragen@pobox.com>       Kragen Sitaker     <http://www.pobox.com/~kragen/>
Perilous to all of us are the devices of an art deeper than we possess
ourselves.
       -- Gandalf the White [J.R.R. Tolkien, "The Two Towers", Bk 3, Ch. XI]