> Date: Wed, 13 Oct 2010 13:26:30 +0200 > From: Pawel Jakub Dawidek <[email protected]> > Sender: [email protected] > > On Wed, Oct 13, 2010 at 11:47:41AM +0200, Stefan Bethke wrote: > > Am 13.10.2010 um 10:20 schrieb Pawel Jakub Dawidek: > > > > > On Tue, Oct 12, 2010 at 11:33:11PM -0700, Jeremy Chadwick wrote: > > >> On Wed, Oct 13, 2010 at 08:29:06AM +0200, Stefan Bethke wrote: > > >>> That explains the mechanism, but not the rationale. Or is it just an > > >>> unintended consequence? And how is da2p1 different from ufs/mylabel? > > >>> (Mount da2p1 and ufs/mylabel is removed, but not the other way around.) > > >> > > >> Pulling in pjd@ who can probably shed some light on this. > > > > > > The ufs/mylabel provider is based on da2p1, that's why opening da2p1 > > > makes ufs/mylabel to be removed and not the other way around. > > > > > > The ufs/mylabel provider was created, because when da2p1 provider was > > > created and LABEL class tasted it, it discovered that this provider > > > contains UFS file system with 'mylabel' volume label, so the LABEL class > > > created ufs/mylabel provider. Now when you open da2p1 for writing, the > > > LABEL class destroys ufs/mylabel, because you may decide to change > > > metadata on da2p1, for example you may choose to destroy UFS in there or > > > change the volume label. When write open count on da2p1 goes down to > > > zero, the LABEL class will be given da2p1 provider for tasting once > > > again, so it can rediscover (possibly modified) volume label. > > > > > > The class may choose to ignore the spoil event from GEOM (it is send on > > > first open for write), but if it isn't based on autodiscovering > > > metadata. For example the NOP class ignores this event, because it > > > doesn't care about metadata of provider it is based on. > > > > > > If we choose to ignore the spoil event in the LABEL class we will end up > > > with stale info, eg. open da2p1 for writing, change its volume label and > > > mount it and you will still have old label in /dev/ufs/. > > > > Thanks a lot (and also to Andrey), that really makes it clear to me! > > > > I just wish there was an easy way to keep the labels around even while > > someone has the provider open for writing, but I now understand that this > > requires some significant changes. > > The changes aren't significant. We could eventually ignore spoil event > and keep labels around even when underlying provider is opened for > writing risking the label is stale. We could then only update or remove > the label on retaste event (when underlying provider's open write count > goes down to zero). > > Currently when we do, eg. > > # dd if=/dev/zero of=/dev/da2p1 bs=1m > > This is happening: > > # dd(1) opens da2p1 for writing > # GEOM sends spoil event to all consumers of da2p1 > # LABEL class destroys /dev/ufs/mylabel provider > # dd(1) finishes and closes da2p1 > # GEOM sends taste event to all GEOM classes > # LABEL class finds no metadata and ignores da2p1 > > With the new world order this would look like this: > > # dd(1) opens da2p1 for writing > # GEOM sends spoil event to all consumers of da2p1 > # LABEL class ignores spoil event > # dd(1) finishes and closes da2p1 > # GEOM sends taste event to all GEOM classes > # LABEL class finds no metadata on da2p1 and destroys /dev/ufs/mylabel
Thanks! Thi explains most of what I see, but there is one thing that is not explained. That is the devd showing a CREATE for the partition (e.g. da0s2d) every time the partition is either mounted or umounted, regardless of whether it is mounted by device or label. There is never a DESTROY event. this is both counter-intuitive, but hard to program around. -- R. Kevin Oberman, Network Engineer Energy Sciences Network (ESnet) Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab) E-mail: [email protected] Phone: +1 510 486-8634 Key fingerprint:059B 2DDF 031C 9BA3 14A4 EADA 927D EBB3 987B 3751 _______________________________________________ [email protected] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "[email protected]"
