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    SubjectRe: Encrypted Filesystem
    Ah, can someone explain why encrypted loopback doesn't solve this?

    JLC

    On Tue, Jan 27, 2004 at 05:01:54PM -0500, Jan Harkes wrote:
    > On Tue, Jan 27, 2004 at 12:43:21AM +0000, Adam Sampson wrote:
    > > Michael A Halcrow <mahalcro@us.ibm.com> writes:
    > >
    > > > - Userland filesystem-based (EncFS+FUSE, CryptoFS+LUFS)
    > >
    > > Going off on a tangent...
    > >
    > > There are all sorts of potentially-interesting things that could be
    > > done if Linux had a userspace filesystem mechanism included in the
    > > standard kernel -- as well as encryption, there's also network
    > > filesystems, various sorts of specialised caching (such as Zero
    > > Install), automounter-like systems, prototyping and so on.
    > >
    > > Is there a technical reason that none of the userspace filesystem
    > > layers have been included in the stock kernel, or is it just that
    > > nobody's submitted any of them for inclusion yet?
    >
    > Ehh, Coda's kernel module does just that. It is used by the userspace
    > cache manager of the Coda Distributed File System.
    >
    > http://www.coda.cs.cmu.edu/
    >
    > But several other projects seem to be using it,
    >
    > http://uservfs.sourceforge.net/
    > http://dav.sourceforge.net/
    >
    > The interface to userspace a bit clumsy to work with, but there are
    > kernel modules for FreeBSD/NetBSD/Solaris and an experimental one for
    > Windows 2000/NT/XP, which makes any significant changes a bit of a pain.
    >
    > It does have it's pecularities, reads and writes are not passed up to
    > userspace, only the open and close VFS calls. This makes the module
    > reasonably quite simple as it doesn't have to deal with VM issues and it
    > isn't susceptible to deadlocks,
    >
    > app wants to read data from a file ->
    > userspace application requires memory allocation to provide this data ->
    > VM tries to write out dirty data associated with the Coda mountpoint ==
    > deadlock
    >
    > So whole file caching keeps the kernel module more portable and
    > simplifies the userspace code. But it makes things like streaming
    > reads/writes or quotas impossible. If you want to provide encryption
    > there you would have to store an unencrypted copy of every open file
    > somewhere on disk or in ramfs/tmpfs and incur the cost of (de)crypting
    > (and (de)compressing) whenever it is opened or closed.
    >
    > Jan
    >
    > -
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