linux-kernel - Re: [PATCH 1/2] vmcore: allow alternate dump capturing methods to export vmcore without is_kdump

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Date:   Mon, 4 Sep 2023 20:04:08 +0530
From:   Hari Bathini <hbathini@...ux.ibm.com>
To:     Baoquan He <bhe@...hat.com>
Cc:     linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Kexec-ml <kexec@...ts.infradead.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Sourabh Jain <sourabhjain@...ux.ibm.com>,
        Mahesh J Salgaonkar <mahesh@...ux.ibm.com>,
        Dave Young <dyoung@...hat.com>
Subject: Re: [PATCH 1/2] vmcore: allow alternate dump capturing methods to
 export vmcore without is_kdump_kernel()

Hi Baoquan,

Thanks for the review...

On 03/09/23 9:06 am, Baoquan He wrote:
> Hi Hari,
> 
> On 09/02/23 at 12:34am, Hari Bathini wrote:
>> Currently, is_kdump_kernel() returns true when elfcorehdr_addr is set.
>> While elfcorehdr_addr is set for kexec based kernel dump mechanism,
>> alternate dump capturing methods like fadump [1] also set it to export
>> the vmcore. is_kdump_kernel() is used to restrict resources in crash
>> dump capture kernel but such restrictions may not be desirable for
>> fadump. Allow is_kdump_kernel() to be defined differently for such
>> scenarios. With this, is_kdump_kernel() could be false while vmcore
>> is usable. So, introduce is_crashdump_kernel() to return true when
>> elfcorehdr_addr is set and use it for vmcore related checks.
> 
> I got what is done in these two patches, but didn't get why they need be
> done. vmcore_unusable()/is_vmcore_usable() are only unitilized in ia64.
> Why do you care if it's is_crashdump_kernel() or is_kdump_kernel()?
> If you want to override the generic is_kdump_kernel() with powerpc's own
> is_kdump_kernel(), your below change is enough to allow you to do that.
> I can't see why is_crashdump_kernel() is needed. Could you explain that
> specifically?

You mean to just remove is_kdump_kernel() check in is_vmcore_usable() &
vmcore_unusable() functions? Replaced generic is_crashdump_kernel()
function instead, that returns true for any dump capturing method,
irrespective of whether is_kdump_kernel() returns true or false.
For fadump case, is_kdump_kernel() will return false after patch 2/2.

Thanks
Hari