Re: partially encrypted filesystem

["H. Peter Anvin" <hpa@zytor.com>]

Followup to:  <3FCE8CF5.4030006@pobox.com>
By author:    Jeff Garzik <jgarzik@pobox.com>
In newsgroup: linux.dev.kernel
>
> 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.

	-hpa
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