On Tue, Jun 28 2016 at 4:23pm -0400, Kani, Toshimitsu <toshi.kani@xxxxxxx> wrote: > On Tue, 2016-06-28 at 16:07 -0400, Mike Snitzer wrote: > > On Tue, Jun 28 2016 at 3:37pm -0400, > > Toshi Kani <toshi.kani@xxxxxxx> wrote: > : > > You said in the 0th header: "Patch 1 solves an error when lvremove is > > made to a snapshot device." > > > > I'm not seeing why this patch 1 fixes anything specific to snapshot > > device removal (but I can see why patch 2 makes snapshot creation > > "work"). I'll apply your 2nd patch and see if I can see what you mean. > > > > I actually see this error, without either of your 2 proposed patches > > applied, when I try to create a snapshot of a DAX capable LV: > > > > # lvcreate -s -n snap -L 100M pmem/lv > > device-mapper: reload ioctl on (253:7) failed: Invalid argument > > Failed to lock logical volume pmem/lv. > > Aborting. Manual intervention required. > > Jun 28 15:57:28 rhel-storage-02 kernel: device-mapper: ioctl: can't change > > device type after initial table load. > > Yes, patch 2 fixes this error. > > I have not looked into why lvremove does this, but lvremove to a snapshot > device fails to reload DM table of "<dev>-lvsnap" device (which is marked as > DM_TYPE_BIO_BASED) with DM_TYPE_DAX_BIO_BASED. Patch 1 fixes this error. It looks like a strange intermediate state that lvm2 uses during snapshot removal. Full listing of snapshot related DM tables (before lvremove): pmem-lv-real: 0 6086656 linear 259:0 2048 pmem-lv: 0 6086656 snapshot-origin 253:5 pmem-snap-cow: 0 204800 linear 259:0 6088704 pmem-snap: 0 6086656 snapshot 253:5 253:6 P 8 When removing this snapshot we're wanting to be left with: pmem-lv: 0 6086656 linear 259:0 2048 I augmented the DM core error to be more expressive, resulting in: device-mapper: ioctl: 253:7: can't change device type (from 1 to 4) after initial table load. 1 is DM_TYPE_BIO_BASED and 4 is DM_TYPE_DAX_BIO_BASED -- which makes sense given the linear target is DM_TYPE_DAX_BIO_BASED. The previous DM table for 253:7 was: pmem-snap: 0 6086656 snapshot 253:5 253:6 P 8 The intermediate table that lvm2 is trying to load for 253:7 is: 0 204800 linear 259:0 6088704 (this linear target was previously pmem-snap-cow) > I think it also generally makes sense to allow this case. You're probably right but I need to think about it a little bit more. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
