Proposal for a new I/O library design

Alastair Reid
Tue, 29 Jul 2003 01:20:41 +0100

> If it's not possible to provide a guarantee of File identity then we
> should probably drop the whole idea of File values. 

I haven't been following in enough detail to know if File values are a good 
idea or not but it's maybe worth mentioning that if you're NFS, there's no 
way to test file identity.  IIRC, the problem is that a machine might 
nfs-export overlapping parts of its filesystem so you might have two names 
for the same file.

Alastair Reif

ps (At least in FreeBSD) mmapping an NFS-mounted file can also lead to 
unhappiness.  If you mmap the same NFS-mounted file multiple times, you can 
end up with multiple copies of the same page which leads to chaos when you 
start writing to the pages.  (At least, that was the conclusion we came to 
when trying to understand why libelf produced incorrect results when used 
with NFS-mounted files if compiled with mmapping turned on but produced 
correct results for NFS-mounted files with mmapping turned off and with local 
files (mmapping on or off).