Re: [Xen-devel] [PATCH v2 3/4] makedumpfile/xen: Fail immediately on every architecture if dump level is invalid

[Daniel Kiper <daniel.kiper@xxxxxxxxxx>]

On Tue, Dec 03, 2013 at 05:27:03AM +0000, Atsushi Kumagai wrote:
> On 2013/12/02 23:17:59, kexec <kexec-bounces@xxxxxxxxxxxxxxxxxxx> wrote:
> > Do not try to process Xen crash dump on every architecture if dump level
> > is invalid. Fail immediately and print relevant error message.
> >
> > Signed-off-by: Daniel Kiper <daniel.kiper@xxxxxxxxxx>
> > ---
> >  makedumpfile.c |    4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/makedumpfile.c b/makedumpfile.c
> > index 5a378d1..45f96aa 100644
> > --- a/makedumpfile.c
> > +++ b/makedumpfile.c
> > @@ -7637,14 +7637,14 @@ initial_xen(void)
> >             MSG("Try `makedumpfile --help' for more information.\n");
> >             return FALSE;
> >     }
> > -#ifndef __x86_64__
> > +
> >     if (DL_EXCLUDE_ZERO < info->max_dump_level) {
> >             MSG("Dump_level is invalid. It should be 0 or 1.\n");
> >             MSG("Commandline parameter is invalid.\n");
> >             MSG("Try `makedumpfile --help' for more information.\n");
> >             return FALSE;
> >     }
> > -#endif
> > +
>
> Did you say that dump level 2 or larger are no longer effective even for 
> x86_64 ?
> I thought it works by the patch below, but I'm not sure about Xen.
> So I would like to know why you sent this patch.
>
>
> commit ec5b5835a113cf62a168d4a7354564a38de6b52c
> Author: ken1_ohmichi <ken1_ohmichi>
> Date:   Fri Oct 9 03:05:41 2009 +0000
>
>     [v1.3.4-10] Add dump filtering on an x86_64 xen domain-0.
>
>     This patch adds the dump filtering for excluding unnecessary pages (cache
>     pages, user process data pages, and free pages) on on x86_64 xen domain-0.
>
>     On the existing makedumpfile (v1.3.3 or former), a user could specify 0
>     or 1 only as a dump_level. By this patch, he/she can specify 2 or larger
>     also as a dump_level.
>
>     Now, this feature is effective on x86_64 machine only.

Hmmm... Thanks for this. I missed this patch. However, it looks that I
do not understand something. AIUI, from Xen point of view we are not able
to use dump level higher than 1 because there is no e.g. cache pages (it
looks that we could also skip free pages but this stuff is not implemented).
Above mentioned patch suggest that there is a way to extract just only Dom0
stuff taking into account Linux internals only. If my reasoning is true
then dump level higher than 1 is possible only if we look at Dom0 from Linux
point of view. However, I can not find any description how to do that.
So I am CC-ing Ken'ichi as author of this patch but I do not know that
he works for NEC still.

Daniel

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