Date: Mon, 9 Jan 2012 16:17:18 -0800 (PST) From: Don Lewis <truckman@FreeBSD.org> To: dougb@FreeBSD.org Cc: arch@FreeBSD.org, adrian@FreeBSD.org, alfred@FreeBSD.org Subject: Re: [patch] allow crash dumps to Linux swap partitions Message-ID: <201201100017.q0A0HItk037943@gw.catspoiler.org> In-Reply-To: <4F0AB07D.1060208@FreeBSD.org>
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On 9 Jan, Doug Barton wrote: > On 01/09/2012 01:11, Don Lewis wrote: >> On 9 Jan, Adrian Chadd wrote: >>> .. doesn't linux swap have some metadata somewhere? >> >> Darned if I know, but it doesn't seem to care about FreeBSD swap data >> overwriting its swap partition. > > Have you had to do anything special for linux boot? I multi-boot myself > and would love to be able to save space on my laptop by only having one > universal swap partition. I started to look at doing this but found > various docs that said don't unless you are able to recreate the > metadata that Adrian referenced above. Looks like this is safe to do. There is some code in swaponsomething() to avoid the first two page-size blocks of the swap file to avoid overwriting the BSD label if the swap partition starts at sector zero of a BSD partition. Here's the confirmation that my Linux swap metadata is unmolested: # dd if=/dev/da0s4 bs=4k count=1 | strings 1+0 records in 1+0 records out 4096 bytes transferred in 0.012188 secs (336063 bytes/sec) jvLI SWAP-sda4 SWAPSPACE2 I think UFS always avoided this problem, but I seem to remember SunOS fixing this problem for swap. Before Sun fixed this, SunOS would stop on the first sector of the swap partition. If you decided to use a dedicated swap disk and started the swap partition at sector zero, the label would get blown away as soon as you started using swap space.home | help
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