Date: Thu, 31 Oct 2024 15:33:39 -0700 From: Ravi Pokala <rpokala@freebsd.org> To: Justin Hibbits <jhibbits@FreeBSD.org>, <freebsd-hackers@FreeBSD.org>, <freebsd-arch@freebsd.org> Subject: Re: Direct dumped kernel cores Message-ID: <63B5260F-C835-4BFF-92ED-767AD0CEFE05@panasas.com> In-Reply-To: <20241031182354.14fa48aa@ralga.knownspace> References: <20241031182354.14fa48aa@ralga.knownspace>
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Hi Justin, So, this is like the 'crashkernel' thing Linux has, where it kexec()s an al= ternate kernel when the main one panics? I haven't looked at the patch -- most of it will be way out of my expertise= -- but what, if anything, is done to make sure the on-disk state of the tar= get filesystem is okay, before the "rescue" kernel starts writing to it? Thanks, Ravi (rpokala@) =EF=BB=BF-----Original Message----- From: <owner-freebsd-arch@FreeBSD.org <mailto:owner-freebsd-arch@FreeBSD.or= g>> on behalf of Justin Hibbits <jhibbits@FreeBSD.org <mailto:jhibbits@FreeB= SD.org>> Date: Thursday, October 31, 2024 at 15:23 To: <freebsd-hackers@FreeBSD.org <mailto:freebsd-hackers@FreeBSD.org>>, <fr= eebsd-arch@freebsd.org <mailto:freebsd-arch@freebsd.org>> Subject: Direct dumped kernel cores Hi everyone, At Juniper we've been using a so-called 'rescue' kernel for dumping vmcores directly to the filesystem after a panic. We're now contributing this feature, implemented by Klara Systems, to FreeBSD, and looking for feedback. I posted a review at https://reviews.freebsd.org/D47358 <https://reviews.freebsd.org/D47358>; = for anyone interested. Interesting bits to keep in mind: * It requires a 2-stage build process, one to build the rescue kernel, the other to build the main kernel, which embeds the rescue kernel inside its image. This might need some further work. * Thus far it's been implemented for amd64 and arm64, once proven out, other architectures (powerpc64/le, riscv64) can follow suit. * Kernel environment bits to pass down to the rescue kernel are prefixed `debug.rescue.`, for instance `debug.rescue.vfs.root.mountfrom`. There are many more details in the review summary. We'd love to get feedback from anyone interested. Thanks, Justin Hibbits
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