Date: Wed, 15 Nov 2017 20:46:36 -0500 From: Ed Maste <emaste@freebsd.org> To: Warner Losh <imp@bsdimp.com> Cc: "Rodney W. Grimes" <rgrimes@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: r325860 - head/sbin/newfs Message-ID: <CAPyFy2DBB%2BrTZak8urufxqTxohKKv3%2BryxiteDugxnw-hsaS0g@mail.gmail.com> In-Reply-To: <CANCZdfpN3Q68rxcGn75BCUwv47__=5p_=N%2BPpoqqQbnJTOb8zw@mail.gmail.com> References: <201711151840.vAFIefKV002185@repo.freebsd.org> <201711151847.vAFIlGD9052509@pdx.rh.CN85.dnsmgr.net> <CAPyFy2BMDoA%2Bs76ddyNBYo1iC7TZq99_MNZi%2BmHFV6iAgQxgbQ@mail.gmail.com> <CANCZdfpN3Q68rxcGn75BCUwv47__=5p_=N%2BPpoqqQbnJTOb8zw@mail.gmail.com>
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On 15 November 2017 at 19:36, Warner Losh <imp@bsdimp.com> wrote: > > On Wed, Nov 15, 2017 at 5:05 PM, Ed Maste <emaste@freebsd.org> wrote: >> >> On 15 November 2017 at 13:47, Rodney W. Grimes >> <freebsd@pdx.rh.cn85.dnsmgr.net> wrote: >> >> Author: emaste >> >> Date: Wed Nov 15 18:40:40 2017 >> >> New Revision: 325860 >> >> URL: https://svnweb.freebsd.org/changeset/base/325860 >> >> >> >> Log: >> >> newfs: warn if newer than kernel >> >> >> >> Creating a UFS filesystem with a newfs newer than the running kernel, >> >> and then mounting that filesystem, can lead to interesting failures. >> >> >> >> Add a safety belt to explicitly warn when newfs is newer than the >> >> running kernel. >> > >> > You should probably make the warning if (newer || older) as >> > either is likely to have interesting side effects, as are >> > mounting ufs file systems on different versions. >> >> Why would an older newfs cause trouble? Forward compatibility should be >> fine > > The only scenario that 'old' would cause problems is that if you did a newfs > with a new binary on a new kernel, mounted the file system, wrote files to > it, then rebooted with an old kernel, mounted the filesystem there, writing > new files to it, and then unmounting and running with a new kernel. Right, but that's not older newfs. AFAICT there's no reason at all for a (newer || older) warning. > I'm not sure that the new safety belt is reasonable. Today it's fine, but > over time it will start producing false-positive warnings since the real > issue is just before/after the cg change, not old/new in general. I'd be > tempted to make a check against newfs being >= 1200046 while the kernel is < > 1200046. There wasn't a specific bump for this change to sys/param.h, but > this version was bumped within a few hours of Kirk's change. Well, we don't in general support using a userland newer than the running kernel, other than on a best-effort basis to facilitate upgrades and development. This one is only a warning so I don't see much harm in leaving it in place, and it would catch any new cases of a similar nature. If such a warning was already in place we might have avoided the issue where our snapshots produced checksum mismatch messages. But I don't have a strong objection to a hardcoded version check.
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