Re: Toronto Filsystem?

Werner Almesberger (
Tue, 3 Mar 1998 16:54:57 +0100 (MET)

Trever Adams wrote:
>> From: "Benjamin C.R. LaHaise"
>> Actually, this is easier than it seems. A simple restriction that makes
>> everything work well is to require that all underlying layers be made
>> read-only, which avoids a mess of consistency problems. Then, use a top
>> layer that supports sparse files. Reading a file becomes: try layer one -
>> oh, not there; try layer 2... No, I don't have working code yet.
> Not cool at all. Once the original file owner updates the file (say the
> group agrees on a new standard, or root updates the file) any way but
> clean implimentation and write of the entire modified file becomes
> corrupted.

So you'd have to make "per-block COW" behaviour a mount option. With some
media (e.g. CD-ROM) you can be very sure that they won't change, so such
a shortcut is perfectly valid.

- Werner

 / Werner Almesberger, DI-ICA,EPFL,CH /

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