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    SubjectRe: XFS: how to NOT null files on fsck?
    Chris Wedgwood wrote:
    > On Tue, Jul 13, 2004 at 07:25:29AM +0000, Anton Ertl wrote:
    > > A secure FS must ensure that other people's deleted data does not
    > > end up in the file. AFAIK FSs don't record owners for free blocks,
    > > so they can only ensure this by zeroing the blocks.
    > How can free blocks have an owner? They wouldn't be free then.

    It would be the former owner of the block.

    > > So I doubt that you will see any different behaviour from an FS that
    > > keeps only meta-data consistent and writes meta-data before data.
    > You do, some fs' will return stale data.

    Stale data yes, but probably not stale data from blocks that were
    formerly free (or the file system is insecure).

    > > It's too hard to fix the applications, since there is no easy way to
    > > test that they are really fixed.
    > No, it's not hard to fix the applications and it's easy to tell if
    > they are fixed.

    So, how do you tell?

    > > Also, the number of applications is much higher than the number of
    > > file systems.
    > You don't fix all applications, only ones where data is critical and
    > their handling of it is poor. MTAs like postfix don't have a problem
    > for example, they are generally written well.

    Where is data not critical? I had such a problem even with a
    widely-used application like GNU Emacs (many years ago, may be fixed
    now), casting doubt on your claim that fixing the application is easy.

    > > The file system should provide something that I call in-order
    > > semantics, i.e., that the disk state always represents an existing
    > > (possibly old) logical state of the FS, not some state that never
    > > existed, or some existing state with missing data.
    > ext3 and reiserfs have what amounts to this as an option right now.
    > It has some performance implications but I'm told works great.

    You mean ext3 data=journal? The last I heard about it was that it was

    ext3 data=ordered will probably also work better in most cases than an
    FS with eager meta-data updates (like, apparently, XFS), but I don't
    think it guarantees in-order semantics.

    - anton
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