Re: how to make Debian less fragile (long and philosophical)

[Daniel Burrows <Daniel_Burrows@brown.edu>]

On Tue, Aug 17, 1999 at 05:52:53PM -0400, Steve Willer was heard to say:
> The problem is that the libraries aren't readonly because they in turn
> have dependencies on other libraries. During the fixup stage, the loader
> definitely has to write to those mmap'd locations. Looking quickly through
> the source shows that ldso uses MAP_PRIVATE on the mmap call. The only way
> libraries could be shared is with children, then. Forked children would
> share the page no matter what because of copy-on-write, and forked+exec'd
> children would presumably have the old mmap's clobbered.

  Aah.  That took me a moment but it makes sense :)  However I
wonder whether this is really as bad as it sounds.  This would just mean that
the pages containing locations that need to be written to would be held in
a private copy, the rest of the file could be shared as usual.  How much of
a problem this is obviously depends on the particular library, but given that
most programs on my system (in a quick glance at top) claim to be sharing over
half their address space, I suspect that it may work fairly well.  (I'm assuming
of course that pages which have been modified from the library image are not
listed as shared, this could be a dumb assumption)

  Daniel

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Everything else is tied for first.