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

[Atsushi Kumagai <kumagai-atsushi@xxxxxxxxxxxxxxxxx>]

On 2013/12/04 4:45:42, kexec <kexec-bounces@xxxxxxxxxxxxxxxxxxx> wrote:
> 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. 

I've reviewed the code for Xen, my understanding is the same as yours.
The memory regions corresponding to hypervisor and DomU will remain even if
specifying the dump level higher than 1.

> 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.

I'm sorry but I missed your point. Did you mention a lack of description
in man page about an effect when specifying the dump level higher than 1
for Xen's memory ?
At least, I still think this patch is wrong because any dump level is
effective for x86_64.

BTW, Ken'ichi still work for NEC but he is busy on other projects.


Thanks
Atsushi Kumagai

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