Date: Wed, 29 Mar 2017 15:55:48 -0600 From: Warner Losh <imp@bsdimp.com> To: Poul-Henning Kamp <phk@phk.freebsd.dk> Cc: John Baldwin <jhb@freebsd.org>, Ngie Cooper <ngie@freebsd.org>, src-committers <src-committers@freebsd.org>, "svn-src-all@freebsd.org" <svn-src-all@freebsd.org>, "svn-src-head@freebsd.org" <svn-src-head@freebsd.org> Subject: Re: svn commit: r316132 - head/sys/boot/i386/boot2 Message-ID: <CANCZdfr2eRRMQy-uwXDhxT0z88CBKwtkg2e_jFBOg%2Bs_L8=FYg@mail.gmail.com> In-Reply-To: <46812.1490823365@critter.freebsd.dk> References: <201703290930.v2T9U3x9087583@repo.freebsd.org> <7448826.asYms2TLO2@ralph.baldwin.cx> <46812.1490823365@critter.freebsd.dk>
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On Wed, Mar 29, 2017 at 3:36 PM, Poul-Henning Kamp <phk@phk.freebsd.dk> wrote: > -------- > In message <7448826.asYms2TLO2@ralph.baldwin.cx>, John Baldwin writes: >>On Wednesday, March 29, 2017 09:30:03 AM Ngie Cooper wrote: > >>> Log: >>> Parameterize out 7680 (15 * 512) as BOOT2SIZE, similar to sys/boot/i386/zfsboot/... >>> >>> This is being done to make it easier to change in the future--this action might be >>> needed sooner rather than later because of gcc 6.3.0 bailing, stating that there >>> is negative free space left (deficit) in the boot2 bootloader. >>> >>> MFC after: 2 months >>> Sponsored by: Dell EMC Isilon >> >>This can't be changed. It's baked into the BSD disklabel format. > > No it is not, it is baked into FFS, and for UFS2 0, 8, 64 and 256K works. Technically, this is correct. Practically, I'm not sure we can ever really change it. There are too many tools, scripts, etc that just know it's 8k, even though most UFS2 systems start 64k into the volume. UFS1 systems are still around, and there the limit is a hard limit. And if we grow it, we run the risk of corrupting data beyond the 8k area we've traditionally used for this. So the constants are easy enough to change and it seems like it might be OK. However, doing it in a safe, anti-foot-shooting way will be the real elbow grease should someone seriously contemplate the change, especially since the foot-shooting involved has the potential for filesystem corruption... But gcc 6.3 likely just needs a little TLC experimenting with its different code generation flags... Warner
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