[Btrfs-devel] transaction ioctls

[Chris Mason]

On Tuesday 22 April 2008, Evgeniy Polyakov wrote:
> Hi.
>
> On Tue, Apr 22, 2008 at 04:55:37PM -0400, Chris Mason 
(chris.mason at oracle.com) wrote:
> > > The transactions generally look like
> > >
> > >  write(a)
> > >  setxattr(a)
> > >  write(b)
> > >  setxattr(b)
> >
> > Hmm, is this whole thing the atomic unit, or can a and b be done
> > separately?
>
> No, main idea is to bind very different operations together and make
> them look atomic from userspace point of view. But transactions are
> nothing without ability to correctly unroll them on demand.
> Transaction can include any operation with data and metadata.

Transaction rollback from a filesystem point of view is a reboot.  Real 
database style transactions with rollback and isolation from other procs etc 
etc are outside the scope of Btrfs.

-chris