CC'ing linux-unionfs On Mon, Jan 26, 2015 at 06:00:35PM +0100, Miklos Szeredi wrote: > On Fri, Jan 23, 2015 at 7:03 PM, Eric Jones <ejones <at> cray.com> wrote: > > Hi. Thanks for overlayfs. > > > > We're using overlayfs, and we're trying to deal with the "undefined" > > behavior when modifying the lower layer. The approach we are taking is to > > lazy unmount all overlays, modify the lower layer, and remount with the > > same upper/lower. > > > > Would you expect processes with references to the lazily unmounted > > overlayfs to behave? Even if the overlay is immediately recreated? > > While referencing the old overlay they will behave in an undefined > way, regardless of the recreated overlay. > > Now "undefined" does not necessarily mean it will do something bad. > Depends on what you expect it to do... > > What's the use case? Why and how are you modifying the lower layer?
Consider managing /opt on a very large diskless cluster. Lower layer is NFS. Upper layer is tmpfs. Upper has portions of /opt we want in memory for performance considerations. Lower could be one of: server:/var/images/opt_A server:/var/images/opt_B server:/var/images/opt_C server:/var/images/opt_XXXX Upper is tmpfs /.opt and they are overlayfs mounted on /opt. So this would be a typical mount command: mount -t overlayfs -olowerdir=/var/images/opt_A,upperdir=/.opt none /opt 1. Will creating new verions of /var/images/opt_XXXX on the NFS server affect existing overlayfs mounts? The docs say modifying the lower filesystem is not allowed, but will anything "bad" happen if we are just adding a sibling directory tree that is not yet overlay mounted? 2. We switch to a new /var/images/opt_XXXX by doing a lazy unmount of the old and mounting the new. Will processes with outstanding references see broken pwd/cwd? Corruption? > > Thanks, > Miklos > > PS. Would you mind including the unionfs mailing list > <linux-unionfs@vger.kernel.org> in the discussion? -- To unsubscribe from this list: send the line "unsubscribe linux-unionfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
