From: Theodore Ts'o Subject: Re: [PATCH] vfs: freeze filesystems just prior to reboot Date: Fri, 19 May 2017 14:20:57 -0400 Message-ID: <20170519182057.qyx3sevm4vatff6a@thunk.org> References: <20170519002032.GA21202@birch.djwong.org> <1495202431.1896310.982081664.066926F8@webmail.messagingengine.com> <20170519152734.qd4lf32e7wst4jdh@thunk.org> <1495211669.1931975.982263184.0F641F32@webmail.messagingengine.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "Darrick J. Wong" , xfs , linux-fsdevel , linux-ext4 To: Colin Walters Return-path: Content-Disposition: inline In-Reply-To: <1495211669.1931975.982263184.0F641F32@webmail.messagingengine.com> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Fri, May 19, 2017 at 12:34:29PM -0400, Colin Walters wrote: > > One of the things that came up when Darrick and I discussed this on > > the weekly ext4 developer's conference call was our mutual wonderment > > that none of the userspace tools implemented a reboot by created a > > tmpfs chroot, pivoting into the chroot, and then unmounting all of the > > remaining file systems. > > On general purpose systems we have a tmpfs chroot already: the initramfs. Aren't we discarding the initramfs after we've pivoted away from it, to save on memory? Keeping the tmpfs chroot around forever would be a waste of memory, and in some cases, especially if you are using a distribution kernel, the initramfs chroot can be rather large. Creating an tmpfs chroot that was only good enough to manage the shutdown would be pretty easy, though; the number of files you would need would be quite very few in number. > That narrows the problem down to keeping `/boot` consistent at > shutdown time. AIUI, a problem here is that XFS doesn't flush the > journal on `syncfs`, only on unmount? And from what I can tell, > even the `XFS_IOC_FREEZE` ioctl won't do that either. I believe the log *is* checkpointed on an XFS_IOC_FREEZE. - Ted