Hi, I've been analyzing why fstest generic/081 fails when the backing device is capable of DAX. The problem boils down to the failure of: lvm vgcreate -f vg0 /dev/pmem0 lvm lvcreate -L 128M -n lv0 vg0 lvm lvcreate -s -L 4M -n snap0 vg0/lv0 The last command fails like: device-mapper: reload ioctl on (253:0) failed: Invalid argument Failed to lock logical volume vg0/lv0. Aborting. Manual intervention required. And the core of the problem is that volume vg0/lv0 is originally of DM_TYPE_DAX_BIO_BASED type but when the snapshot gets created, we try to switch it to DM_TYPE_BIO_BASED because now the device stops supporting DAX. The problem seems to be introduced by Ross' commit dbc626597 "dm: prevent DAX mounts if not supported". The question is whether / how this should be fixed. The current inability to create snapshots of DAX-capable devices looks weird and the cryptic failure makes it even worse (it took me quite a while to understand what is failing and why). OTOH I see the rationale behind Ross' change as well. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
