Issue with 'Unknown Error: -512'

[Brandon Falk]

Hello,

In recent branches (confirmed with 224119) builds compiled with clang 
happen to throw 'Unknown error: -512' in a lot of places, making the 
system unusable. (Untested on gcc compiled systems). Originally I 
thought the problem was with specific programs, then I narrowed it down 
to file I/O, and now I've narrowed it down to open() with O_TRUNC. 
Without O_TRUNC there seems to be no issues whatsoever. With O_TRUNC on 
open() it fails with that 'Unknown error: -512' every other time you run 
the program. Common issues, portsnap is affected, making it impossible 
to fetch/extract ports. As well as redirecting output in shells eg `echo 
'hi' > test` fails every other try. You have the same issue with text 
editors like `edit` where it fails every other save. There are no issues 
with `echo 'hi' >> test` as there is no O_TRUNC, it only seems to be an 
O_TRUNC error.

Any tips? Otherwise I'll be looking into this today myself.

-Brandon Falk