Date: Wed, 11 Jan 2012 17:13:02 -0800 From: John-Mark Gurney <jmg@funkthat.com> To: Don Lewis <truckman@freebsd.org> Cc: arch@freebsd.org, adrian@freebsd.org, nvass@gmx.com, alfred@freebsd.org, dougb@freebsd.org Subject: Re: [patch] allow crash dumps to Linux swap partitions Message-ID: <20120112011301.GI52468@funkthat.com> In-Reply-To: <201201091009.q09A9NQb025487@gw.catspoiler.org> References: <4F0AB63D.2040503@gmx.com> <201201091009.q09A9NQb025487@gw.catspoiler.org>
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Don Lewis wrote this message on Mon, Jan 09, 2012 at 02:09 -0800:
> On 9 Jan, Nikos Vassiliadis wrote:
> > On 1/9/2012 11:25 AM, Doug Barton wrote:
> >> Actually I'm fairly confident that we write dumps backwards from the end
> >> of the swap partition. It's done that way on purpose in case fsck'ing
> >> causes the system to swap, it may still be possible to save the dump.
> >
> > So, dumping core is safe, but not sharing the swap area...
> > It would be nice to be able to do that.
>
> According to the mkswap(8) man page (which hasn't been updated
> since 2.2 even though the machine is running a 2.6 kernel) on a nearby
> Linux machine, the metadata stored in the first page of the swap
> partition. It looks like we could safely coexist if we skipped the first
> page of the partition. Otherwise Linux will want mkswap to be run on the
> partition before it will swap to the partition.
Don't we already skip the first 8k of the swap partition because back
in the day when bsdlabel's partition sector 0 was the same as the
slice sector 0, and so if any FS or swap wrote to the first 8k, it
would overwrite the bsdlabel?
--
John-Mark Gurney Voice: +1 415 225 5579
"All that I will do, has been done, All that I have, has not."
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