linux-kernel - Re: [PATCH v4 0/5] kexec: reorganize sysfs interface and add new kexec sysfs

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Message-ID: <a27ecae9-a001-4e57-86cf-09c2cc3d6371@linux.ibm.com>
Date: Sat, 15 Nov 2025 21:39:40 +0530
From: Sourabh Jain <sourabhjain@...ux.ibm.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org, Aditya Gupta <adityag@...ux.ibm.com>,
        Baoquan he <bhe@...hat.com>, Dave Young <dyoung@...hat.com>,
        Hari Bathini <hbathini@...ux.ibm.com>, Jiri Bohac <jbohac@...e.cz>,
        Madhavan Srinivasan <maddy@...ux.ibm.com>,
        Mahesh J Salgaonkar <mahesh@...ux.ibm.com>,
        Pingfan Liu <piliu@...hat.com>,
        "Ritesh Harjani (IBM)" <ritesh.list@...il.com>,
        Shivang Upadhyay <shivangu@...ux.ibm.com>,
        Sourabh Jain <sourabhjains@...ux.ibm.com>,
        Vivek Goyal <vgoyal@...hat.com>, linuxppc-dev@...ts.ozlabs.org,
        kexec@...ts.infradea
Subject: Re: [PATCH v4 0/5] kexec: reorganize sysfs interface and add new
 kexec sysfs



On 15/11/25 04:55, Andrew Morton wrote:
> On Fri, 14 Nov 2025 10:44:59 +0530 Sourabh Jain <sourabhjain@...ux.ibm.com> wrote:
>
>> All existing kexec and kdump sysfs entries are moved to a new location,
>> /sys/kernel/kexec, to keep /sys/kernel/ clean and better organized.
>> Symlinks are created at the old locations for backward compatibility and
>> can be removed in the future [02/05].
>>
>> While doing this cleanup, missing ABI documentation for the old sysfs
>> interfaces is added, and those entries are marked as deprecated
>> [01/05 and 03/05]. New ABI documentation is also added for the
>> reorganized interfaces. [04/05]
>>
>> Along with this reorganization, a new sysfs file,
>> /sys/kernel/kexec/crash_cma_ranges, is introduced to export crashkernel
>> CMA reservation details to user space [05/05]. This helps tools
>> determine the total crashkernel reserved memory and warn users that
>> capturing user pages while CMA is reserved may cause incomplete or
>> unreliable dumps.
> Patchset does three unrelated things in remarkably random order.
>
> 1: Document existing stuff
>
> 	Great, thanks, in it goes.
>
> 2: export crashkernel CMA reservation to userspace
>
> 	Well, OK, probably reasonable, didn't look closely.
>
> 3: Alter longstanding userspace ABI with deprecation plan
>
> 	Whoa, tricky, needs careful consideration.
>
>
> So can we please prepare and consider this material in three separate
> patchsets?  In the above order, I suggest.

Yeah sure.

The question here is where to add the new CMA reservation sysfs.
Should I place it under /sys/kernel/ or create /sys/kernel/kexec and
add it there?

Since I am proposing that all kexec sysfs entries move to the new
location /sys/kernel/kexec, I am going to add the CMA reservation
sysfs under /sys/kernel/kexec to avoid creating a symlink for this
entry later in my third patch series.

- Sourabh