Date: Thu, 31 Oct 2024 16:32:51 -0600 From: Warner Losh <imp@bsdimp.com> To: Justin Hibbits <jhibbits@freebsd.org> Cc: freebsd-hackers@freebsd.org, freebsd-arch@freebsd.org Subject: Re: Direct dumped kernel cores Message-ID: <CANCZdfrobB-ZM3aMmD%2BAsjud3%2BM-_kkMB3SqTpaKTxtmY1x3Yg@mail.gmail.com> In-Reply-To: <20241031182354.14fa48aa@ralga.knownspace> References: <20241031182354.14fa48aa@ralga.knownspace>
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--000000000000c2670d0625cd66ec Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, Oct 31, 2024 at 4:24=E2=80=AFPM Justin Hibbits <jhibbits@freebsd.or= g> wrote: > 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 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`. > First off, this is kinda cool. I've wanted this occasionally when my swap partition is too small (though in my case, it was easy enough to add anothe= r drive to the system that was panicking and dump to that). I do have a question: I'm curious why you didn't follow the Linux lead of having a kexec_load(2) system call to load the 'rescue kernel' to make this more generic. That would make the leap to having full kexec support (eg reboot(CMD_KEXEC) a lot easier to implement. Warner > There are many more details in the review summary. > > We'd love to get feedback from anyone interested. > > Thanks, > Justin Hibbits > > --000000000000c2670d0625cd66ec Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable <div dir=3D"ltr"><div dir=3D"ltr"><br></div><br><div class=3D"gmail_quote">= <div dir=3D"ltr" class=3D"gmail_attr">On Thu, Oct 31, 2024 at 4:24=E2=80=AF= PM Justin Hibbits <<a href=3D"mailto:jhibbits@freebsd.org">jhibbits@free= bsd.org</a>> wrote:<br></div><blockquote class=3D"gmail_quote" style=3D"= margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-lef= t:1ex">Hi everyone,<br> <br> At Juniper we've been using a so-called 'rescue' kernel for dum= ping<br> vmcores directly to the filesystem after a panic.=C2=A0 We're now<br> contributing this feature, implemented by Klara Systems, to FreeBSD, and<br= > looking for feedback. I posted a review<br> at <a href=3D"https://reviews.freebsd.org/D47358" rel=3D"noreferrer" target= =3D"_blank">https://reviews.freebsd.org/D47358</a>; for anyone interested.<b= r> <br> Interesting bits to keep in mind:<br> * It requires a 2-stage build process, one to build the rescue kernel,<br> =C2=A0 the other to build the main kernel, which embeds the rescue kernel<b= r> =C2=A0 inside its image.=C2=A0 This might need some further work.<br> * Thus far it's been implemented for amd64 and arm64, once proven out,<= br> =C2=A0 other architectures (powerpc64/le, riscv64) can follow suit.<br> * Kernel environment bits to pass down to the rescue kernel are<br> =C2=A0 prefixed `debug.rescue.`, for instance<br> =C2=A0 `debug.rescue.vfs.root.mountfrom`.<br></blockquote><div><br></div><d= iv>First off, this is kinda cool. I've wanted=C2=A0this occasionally wh= en my swap</div><div>partition=C2=A0is too small (though in my case, it was= easy enough to add another</div><div>drive to the system that was panickin= g and dump to that).</div><div><br></div><div>I do have a question: I'm= curious why you didn't follow the Linux lead of having</div><div>a kex= ec_load(2) system call to load the 'rescue kernel' to make this mor= e generic.</div><div>That would make the leap to having full kexec support = (eg reboot(CMD_KEXEC)</div><div>a lot easier to implement.</div><div><br></= div><div>Warner</div><div>=C2=A0</div><blockquote class=3D"gmail_quote" sty= le=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);paddi= ng-left:1ex"> There are many more details in the review summary.<br> <br> We'd love to get feedback from anyone interested.<br> <br> Thanks,<br> Justin Hibbits<br> <br> </blockquote></div></div> --000000000000c2670d0625cd66ec--
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