Re: [PATCH v2] xfs_restore: detect rtinherit on destination

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On Thu, Jun 6, 2019 at 3:37 PM Dave Chinner <david@xxxxxxxxxxxxx> wrote:
>
> On Thu, Jun 06, 2019 at 05:08:12PM -0500, Eric Sandeen wrote:
> > On 6/6/19 4:50 PM, Dave Chinner wrote:
> > > My take on this is that we need to decide which allocation policy to
> > > use - the kernel policy or the dump file policy - in the different
> > > situations. It's a simple, easy to document and understand solution.
> > >
> > > At minimum, if there's a mismatch between rtdev/non-rtdev between
> > > dump and restore, then restore should not try to restore or clear rt
> > > flags at all. i.e the rt flags in the dump image should be
> > > considered invalid in this situation and masked out in the restore
> > > process. This prevents errors from being reported during restore,
> > > and it does "the right thing" according to how the user has
> > > configured the destination directory. i.e.  if the destdir has the
> > > rtinherit bit set and there's a rtdev present, the kernel policy
> > > will cause all file data that is restored to be allocated on the
> > > rtdev. Otherwise the kernel will place it (correctly) on the data
> > > dev.
> > >
> > > In the case where both have rtdevs, but you want to restore to
> > > ignore the dump file rtdev policy, we really only need to add a CLI
> > > option to say "ignore rt flags" and that then allows the kernel
> > > policy to dictate how the restored files are placed in the same way
> > > that having a rtdev mismatch does.
> > >
> > > This is simple, consistent, fulfils the requirements and should have
> > > no hidden surprises for users....
> >
> > Sounds reasonable.  So the CLI flag would say "ignore RT info in the
> > dump, and write files according to the destination fs policy?"
> > I think that makes sense.

Any suggested flag name/prefix for this? Last i checked all the single
letters were taken up?

> *nod*
>
> > Now: do we need to do the same for all inheritable flags?  projid,
> > extsize, etc?  I think we probably do.
>
> I disagree. These things are all supported on all destination
> filesystems, unlike the rtdev. They are also things that can be
> changed after the fact, unlike rtdev allocation policy. i.e. rtdev
> has to be set /before/ restore, just about everything else can be
> set or reset after the fact....
> Cheers,
>
> Dave.
> --
> Dave Chinner
> david@xxxxxxxxxxxxx



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