vfork

[tp at ndm20]

>vfork is a botch.  The way to implement fork on a paged system is to set
>up both processes with identical data page tables as well as text pages,
>and make the data pages read-only.  When a write to a data page causes
>a fault, duplicate the page and make each copy writable.  Swapping gets

According to an AT&T representative at the January uniforum here in dallas,
one of the changes that will soon be made to SysV is to implement the
"Copy-on-modify" protection on a page (exactly what you describe) as part
of the SysV virtual memory code (which does exist in SVR2v4 on the 3b20,
though nobody seems to have ported it (are they releasing it?)).
Other enhancements he mentioned were Dennis Ritchie's Streams package and
a distributed file system (actually the streams package is the implementation
vehicle for the dfs).

The above is subject to a 6 month memory lag. Somebody please correct me
if I'm wrong on these (fast, before the fallout hits), but I'm pretty
sure about those particular items.

Thanks,
Terry Poot
Nathan D. Maier Consulting Engineers
(214)739-4741
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