Coda File System

Re: Theory of writeback (without SHA-1 or other crypto)

From: <>
Date: Sun, 25 Mar 2007 16:07:29 +0200
Hello Satya,

On Sun, Mar 25, 2007 at 09:22:02AM -0400, M. Satyanarayanan wrote:
> Here's another approach that doesn't require use of SHA-1 or
> any other crypographic hash.   It is OS-specific, but the
> change looks simple:
> 1. The Coda kernel module could intercept all  write() calls,
>      but just not pass them up to Venus.  So Venus sees
>     nothing different from today.
> 2. For each open() instance, the Coda kernel module could set a 
>     bit to indicate that a write() was seen.
> 3. On close(), the Coda kernel module uses a new parameter
>    to indicates whether the file had any write()s performed on it.
>    This is an incompatible upgrade, but worth it for the benefits.
>     If no writes were seen, Venus avoids the store of the file.

This would probably work well for systems without mmap(),
it is what you meant with "OS-specific"?

Otherwise I fear that we'd miss possible modifications done via mmap().
It may be used though as another "shortcut" check if there were no mmap()s.

It would be certainly useful for collecting statistics in any case.

Received on 2007-03-25 10:07:28