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SubjectRe: [PATCH 17/38] union-mount: Union mounts documentation
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On Thu, 17 Jun 2010, Valerie Aurora wrote:
> On Thu, Jun 17, 2010 at 10:01:30AM +0200, Alex Riesen wrote:
> > On Tue, Jun 15, 2010 at 20:39, Valerie Aurora <vaurora@redhat.com> wrote:
> > > +git://git.kernel.org/pub/scm/fs/ext2/val/e2fsprogs.git
> > > +
> > > +Currently, whiteout directory entries are not returned to userland.
> > > +While the directory type for whiteouts, DT_WHT, has been defined for
> > > +many years, very little userland code handles them. ??Userland will
> > > +never see fallthru directory entries.
> >
> > This may be a dumb question (I must admit I did only very little research),
> > but how does one cleanup the topmost layer of whiteouts and fallthroughs,
> > so that the entries of lower layer(s) can be made visible again?
>
> I'm not sure how best to do this. We don't want to add more system
> calls. One thought of mine has been to do this offline, when the file
> system is unmounted. For example, e2fsck could add a feature to
> delete whiteouts and fallthrus. Another option is to add a flag to an
> existing system call.

One more advantage of doing whiteouts, etc. with hard links and
extended attributes instead of as special filesystem objects. That
way they are visible (unless part of a union) and can be treated as
normal filesystem objects.

Miklos


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