Date: Thu, 31 Oct 2024 21:07:34 -0400 From: Justin Hibbits <jhibbits@FreeBSD.org> To: Ravi Pokala <rpokala@freebsd.org> Cc: <freebsd-hackers@FreeBSD.org>, <freebsd-arch@freebsd.org> Subject: Re: Direct dumped kernel cores Message-ID: <20241031210734.283a2fb5@ralga.knownspace> In-Reply-To: <63B5260F-C835-4BFF-92ED-767AD0CEFE05@panasas.com> References: <20241031182354.14fa48aa@ralga.knownspace> <63B5260F-C835-4BFF-92ED-767AD0CEFE05@panasas.com>
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On Thu, 31 Oct 2024 15:33:39 -0700 Ravi Pokala <rpokala@freebsd.org> wrote: > Hi Justin, >=20 > So, this is like the 'crashkernel' thing Linux has, where it kexec()s > an alternate kernel when the main one panics? If your description is accurate, then probably. I don't know if the crashkernel thing from Linux existed when this was started, and actually hadn't even heard of it until now. >=20 > 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 target filesystem is okay, before the "rescue" kernel > starts writing to it? Good question. The rescue kernel embeds its own small rootfs it fscks the target fs before writing to it. - Justin >=20 > Thanks, >=20 > Ravi (rpokala@) >=20 > =EF=BB=BF-----Original Message----- > From: <owner-freebsd-arch@FreeBSD.org > <mailto:owner-freebsd-arch@FreeBSD.org>> on behalf of Justin Hibbits > <jhibbits@FreeBSD.org <mailto:jhibbits@FreeBSD.org>> Date: Thursday, > October 31, 2024 at 15:23 To: <freebsd-hackers@FreeBSD.org > <mailto:freebsd-hackers@FreeBSD.org>>, <freebsd-arch@freebsd.org > <mailto:freebsd-arch@freebsd.org>> Subject: Direct dumped kernel cores >=20 >=20 > Hi everyone, >=20 >=20 > 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. >=20 >=20 > 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`. >=20 >=20 > There are many more details in the review summary. >=20 >=20 > We'd love to get feedback from anyone interested. >=20 >=20 > Thanks, > Justin Hibbits >=20 >=20 >=20 >=20 >=20 >=20
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