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    SubjectRe: ext3_ordered_writepage() questions
    On Thu, 2006-03-16 at 13:09 -0500, Theodore Ts'o wrote:
    > > >Yup. Ordered-mode JBD commit needs to write and wait upon all dirty
    > > >file-data buffers prior to journalling the metadata. If we didn't run
    > > >journal_dirty_data_fn() against those buffers then they'd still be under
    > > >I/O after commit had completed.
    > > >
    > > In non-block allocation case, what metadata are we journaling in
    > > writepage() ?
    > > block allocation happend in prepare_write() and commit_write() journaled the
    > > transaction. All the meta data updates should be done there. What JBD
    > > commit are you refering to here ?
    > Basically, this boils down to what is our definition of ordered-mode?
    > If the goal is to make sure we avoid the security exposure of
    > allocating a block and then crashing before we write the data block,
    > potentially exposing previously written data that might be belong to
    > another user, then what Badari is suggesting would avoid this
    > particular problem.

    Yes, if the block allocation is needed, my patch is basically
    no-op, we go through regular code.

    > However, if what we are doing is overwriting our own data with more an
    > updated, more recent version of the data block, do we guarantee that
    > any ordering semantics apply? For example, what if we write a data
    > block, and then follow it up with some kind of metadata update (say we
    > touch atime, or add an extended attribute). Do we guarantee that if
    > the metadata update is committed, that the data block will have made
    > it to disk as well?

    I don't see how we do this today. Yes. Metadata updates are jounalled,
    but I don't see how current adding buffers through journal_dirty_data
    (bh) call can guarantee that these buffers get added to metadata-update
    transaction ?

    > Today that is the way things work, but is that
    > guarantee part of the contract of ordered-mode?

    BTW, thanks Ted for putting this in human-readable terms :)


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