On Tue, 2003-03-04 at 08:48, Tony Gale wrote:
> On Tue, 2003-03-04 at 13:30, Stephen Lord wrote:
> > On Tue, 2003-03-04 at 02:14, Andi Kleen wrote:
> > > On Tue, Mar 04, 2003 at 02:10:08PM +1100, Nathan Scott wrote:
> > > > Support for unwritten extents. Create separate IO completion
> > >
> > > Gratulations. Do they work fully already?
> >
> > Yep, they are all there. The preallocation calls are still restricted
> > to privileged user's, that should get fixed up soon. I also have some
> > ideas for reworking how we use daemons for this and other things - but
> > that may take a little while to show up.
> >
>
> Please excuse my ignorance, but what are "unwritten extents", and should
> I be excited about their support?
Unwritten extents improve the security of the file preallocation
interface in xfs. When you preallocate space in a file, it is not
zeroed on disk, So if you read from it you get old data. Unless
you have unwritten extent support. For this reason the preallocate
calls on linux were restricted to root.
Unwritten extents slow things down when they are used, which is
why they are selectable via a mkfs option:
mkfs -t xfs -d unwritten=1
So nothing too exciting, unless you are attempting to read Irix
created filesystems on linux, or need the preallocation interface
and have security concerns.
Steve
|