concurrent write(2) calls write bad data to file

[Henry Spencer]

> I don't see any obvious reason why this *couldn't* happen on any
> UNIX system that didn't lock the file table entry while a write was
> in progress...  It may be that ... it's *less
> likely* to happen on a system using the V7 file system, but I don't
> see that it's impossible on such a system.

Not impossible at all.  Running the posted test program on utzoo (a vanilla
V7), some NULs show up.  Guy's explanation sounds right.
-- 
"We must choose: the stars or	Henry Spencer @ U of Toronto Zoology
the dust.  Which shall it be?"	{allegra,ihnp4,decvax,pyramid}!utzoo!henry