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

[Atsushi Kumagai]

On 2013/12/10 19:41:54, kexec <kexec-bounces at lists.infradead.org> wrote:
> > > > 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.
>
> Docs are not consistent because man and help displayed from makedumpfile
> are different. Additionally, even man says nothing how to use this feature
> on Xen vmcore file. If you use makedumpfile e.g.
>
> makedumpfile -Ed 2 /proc/vmcore vmcore
>
> it will not work because it uses VMCOREINFO_XEN instead of VMCOREINFO.
> I discovered that if you would like to use feature from above mentioned
> patch you must run makedumpfile in following way:
>
> makedumpfile -Ed 2 -x vmlinux /proc/vmcore vmcore
>
> Then makedumpfile will get info about dom0 directly from vmlinux.

Certainly the documents should be fixed as you said, I'll do it.

> However, It looks that there is another bug which prevents usage
> of this feature. It looks it is related to change in P2M tree Linux
> code. Once P2M levels where changed from 2 to 3. I fixed similar
> issue in crash tool once.

Thanks for your pointing out, I hope that you will fix that issue
also in makedumpfile.

> When are you going to make a new makedumpfile release? I am going
> to fix this issue before next release but now I am quite busy
> with other stuff.

I must release the new version(v1.5.5) in the next week at the latest
because I announced the release date will be the beginning of December
and there are already many patches for v1.5.5.
So I would like to slip that fix you mentioned to v1.5.6.

> Could you apply patches 1, 2 and 4 from this patch series?
> It looks that they are not controversial.

Sure, the three patches will be merged into v1.5.5.


Thanks
Atsushi Kumagai

> Daniel
>
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