Date: Sat, 28 Oct 2017 15:25:13 -0700 From: Kirk McKusick <mckusick@mckusick.com> To: Mark Johnston <markj@FreeBSD.org> Cc: freebsd-fs@FreeBSD.org Subject: Re: softdep as a mount(8) option Message-ID: <201710282225.v9SMPDCZ074228@chez.mckusick.com> In-Reply-To: <20171027153859.GC2385@raichu>
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> Date: Fri, 27 Oct 2017 11:39:00 -0400 > From: Mark Johnston <markj@FreeBSD.org> > To: freebsd-fs@FreeBSD.org > Subject: softdep as a mount(8) option > > Hi, > > I'd like to finally enable the use of SU (not SU+J) on some small UFS > filesystems. The fact that SU is enabled using a flag in the superblock > poses a problem for me, however: the systems containing these > filesystems may at any time be repurposed to run a kernel that supports > SU but contains bugs[*] that render it unusable. I therefore can't > persistently enable SU in these systems. > > I'm wondering if it would be possible to enable SU using a mount > option rather than with a persistent flag. fsck_ffs conditionalizes some > of its logic on whether SU is configured - is this necessary for > correctness? That is, if I run fsck on an unclean filesystem that had > been mounted with SU, and fsck runs as though SU hadn't been configured, > what problems might arise? > > [*] These bugs are a result of local modifications and aren't in > FreeBSD. While it is safe and possible to add soft-updates (but not journalled soft updates) as a mount option, it means that fsck will not know that soft updates were in use, so it will always run in full (slow) mode at boot time. This is why I have not added it as an option. Kirk McKusick
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