linux-kernel - Re: [PATCH v1 07/11] fs/proc/vmcore: introduce PROC_VMCORE_DEVICE_RAM to detect device RAM ranges in 2nd kernel

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Message-ID: <Z0A4Gl1dUINrTTUX@MiWiFi-R3L-srv>
Date: Fri, 22 Nov 2024 15:51:54 +0800
From: Baoquan He <bhe@...hat.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-s390@...r.kernel.org, virtualization@...ts.linux.dev,
	kvm@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	kexec@...ts.infradead.org, Heiko Carstens <hca@...ux.ibm.com>,
	Vasily Gorbik <gor@...ux.ibm.com>,
	Alexander Gordeev <agordeev@...ux.ibm.com>,
	Christian Borntraeger <borntraeger@...ux.ibm.com>,
	Sven Schnelle <svens@...ux.ibm.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Jason Wang <jasowang@...hat.com>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	Eugenio Pérez <eperezma@...hat.com>,
	Vivek Goyal <vgoyal@...hat.com>, Dave Young <dyoung@...hat.com>,
	Thomas Huth <thuth@...hat.com>, Cornelia Huck <cohuck@...hat.com>,
	Janosch Frank <frankja@...ux.ibm.com>,
	Claudio Imbrenda <imbrenda@...ux.ibm.com>,
	Eric Farman <farman@...ux.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v1 07/11] fs/proc/vmcore: introduce
 PROC_VMCORE_DEVICE_RAM to detect device RAM ranges in 2nd kernel

On 11/21/24 at 08:47pm, David Hildenbrand wrote:
> > > 
> > > That would work, but I don't completely like it.
> > > 
> > > (a) I want s390x to select NEED_PROC_VMCORE_DEVICE_RAM instead. Staring at a
> > > bunch of similar cases (git grep "config NEED" | grep Kconfig, git grep
> > > "config ARCH_WANTS" | grep Kconfig), "select" is the common way to do it.
> > > 
> > > So unless there is a pretty good reason, I'll keep
> > > NEED_PROC_VMCORE_DEVICE_RAM as is.
> > 
> > That's easy to satify, see below:
> 
> Yes, this is mostly what I have right now, except
> 
> > 
> > ============simple version=====
> > fs/proc/Kconfig:
> > config NEED_PROC_VMCORE_DEVICE_RAM
> >          def n
> 
> using "bool" here like other code. (I assume you meant "def_bool n", "bool"
> seems to achieve the same thing)

Yes, you are right. I didn't check it carefully.

> 
> > 
...... 
> > ===================
> > fs/proc/Kconfig:
> > config PROVIDE_PROC_VMCORE_DEVICE_RAM
> >          def_bool n
> > 
> > config NEED_PROC_VMCORE_DEVICE_RAM
> >          def_bool n
> > 
> > config PROC_VMCORE_DEVICE_RAM
> >          def_bool y
> >          depends on PROC_VMCORE
> >          depends on NEED_PROC_VMCORE_DEVICE_RAM
> >          depends on PROVIDE_PROC_VMCORE_DEVICE_RAM
> > 
> > drivers/virtio/Kconfig:
> > config VIRTIO_MEM
> >          select PROVIDE_PROC_VMCORE_DEVICE_RAM if PROC_VMCORE
> >                                                ~~~~~~~~~~~~~~
> > 
> > arch/s390/Kconfig:
> > config S390
> >          select NEED_PROC_VMCORE_DEVICE_RAM if PROC_VMCORE
> >                                             ~~~~~~~~~~~~~~
> > ========================
> > 
> > One last thing I haven't got well, If PROC_VMCORE_DEVICE_RAM has had
> > dependency on PROC_VMCORE, can we take off the ' if PROC_VMCORE' when
> > select PROVIDE_PROC_VMCORE_DEVICE_RAM and NEED_PROC_VMCORE_DEVICE_RAM?
> 
> We could; it would mean that in a .config file you would end up with
> "NEED_PROC_VMCORE_DEVICE_RAM=y" with "#PROC_VMCORE" and no notion of
> "PROC_VMCORE_DEVICE_RAM".

Fair enough. I didn't think of this. Then keeping it is obvisouly
better. Thanks.

> 
> I don't particularly like that -- needing something that apparently does not
> exist. Not sure if there is a best practice here, staring at some examples I
> don't seem to find a consistent rule. I can just drop it, not the end of the
> world.
> 
> 
> Did you get to look at the other code changes in this patch set? Your
> feedback would be highly appreciated!

Will try. While I may not have valuable input about virtio-mem code.