Preliminary Agenda and Activities for LSF
On Fri, Apr 1, 2011 at 2:46 PM, Joel Becker <email@example.com> wrote:
> On Fri, Apr 01, 2011 at 09:30:04AM -0700, Amir Goldstein wrote:
>> when writing DIO to indirect mapped file holes, we fall back to buffered write
>> (so we won't expose stale data in the case of a crash) concurrent DIO reads
>> to that file (before data writeback) can expose stale data. right?
>> do you consider this case mixing buffered and DIO access?
>> do you consider that as a problem?
> * * * *I do not consider this 'mixing', nor do I consider it a problem.
> ocfs2 does exactly this for holes, unwritten extents, and CoW. *It does
> not violate the user's expectation that the data will be on disk when
> the write(2) returns.
> * * * *Falling back to buffered on read(2) is a different story; the
> caller wants the current state of the disk block, not five minutes ago.
> So we can't do that. *But we also don't need to.
the issue is with DIO read exposing uninitialized data on disk
is a security issue.
it's not about giving the read what is expects to see.
> * * * *O_DIRECT users that are worried about any possible space usage in
> the page cache have already pre-allocated their disk blocks and don't
> get here.
> "Under capitalism, man exploits man. *Under Communism, it's just
> * the opposite."
> * * * * * * * * * * * * * * * * - John Kenneth Galbraith
> * * * * * * * * * * * *http://www.jlbec.org/
> * * * * * * * * * * * *firstname.lastname@example.org
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