linux-kernel - Re: [PATCH 0/7] Remove unused /dev/oldmem interface

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Date:	Tue, 28 May 2013 10:37:56 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Zhang Yanfei <zhangyanfei.yes@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Simon Horman <horms@...ge.net.au>,
	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/7] Remove unused /dev/oldmem interface

On Sat, May 25, 2013 at 04:25:21PM -0700, Eric W. Biederman wrote:
> Zhang Yanfei <zhangyanfei.yes@...il.com> writes:
> 
> > /dev/oldmem provides the interface for us to access the "old memory" in
> > the dump-capture kernel. Unfortunately, no one actually uses this interface.
> >
> > And this interface could actually cause some real problems if used on ia64
> > where the cached/uncached accesses are mixed. See the discussion from
> > the link: https://lkml.org/lkml/2013/4/12/386.
> >
> > So Eric suggested that we should remove /dev/oldmem as an unused piece of
> > code.
> >
> > Besides, we used a global variable saved_max_pfn to let the capture kernel
> > know the amount of memory that the previous kernel used. And for almost all
> > architectures (except x86. In x86, saved_max_pfn is used by detect_calgary()),
> > the only user of this variable is the read_oldmem interface of /dev/oldmem, so
> > also remove the setting for saved_max_pfn in those architectures.
> 
> Except for the devices.txt update.
> 
> Acked-by: "Eric W. Biederman" <ebiederm@...ssion.com>

Eric,

Should we schedule the removal of this interface after 1-2 releases
and give a warning once if anybody opens /dev/oldmem and tell them
to use /proc/vmcore instead? 

I am kind of inclined towards warning approarch. If there is any xyz
/dev/oldmem user in the wild out there, he/she atleast gets a chance to
migrate to /proc/vmcore.

Thanks
Vivek
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