Re: partially encrypted filesystem

From: H. Peter Anvin
Date: Wed Dec 03 2003 - 23:01:35 EST

Followup to: <3FCE8CF5.4030006@xxxxxxxxx>
By author: Jeff Garzik <jgarzik@xxxxxxxxx>
In newsgroup:
> Linus Torvalds wrote:
> > With an encrypted filesystem, you can't do that. Or rather: you can do it
> > if the filesystem is read-only, but you definitely CANNOT do it on
> > writing. For writing you have to marshall the output buffer somewhere
> > else (and quite frankly, it tends to become a lot easier if you can do
> > that for reading too).
> >
> > And that in turn causes problems. You get all kinds of interesting
> > deadlock schenarios when write-out requires more memory in order to
> > succeed. So you need to get careful. Reading ends up being the much easier
> > case (doesn't have the same deadlock issues _and_ you could do it in-place
> > anyway).
> FWIW zisofs and ntfs have to do this too, since X on-disk compressed
> pages must be expanded to X+Y in-memory pages...

zisofs is read-only, so it doesn't apply.

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