hammer2_mount: devstr="/dev/vn0@testvol"
hammer2_mount: device="/dev/vn0" label="testvol" rdonly=0
hammer2_ondisk: "/dev/vn0" zone=0 id=0 offset=0x0000000000000000 size=0x0000000008000000
hammer2_ondisk: /dev/vn0's size 0x0000000008000000 exceeds device size 0x0000000004000000
mount: Invalid argument
----
[provenance] DF-2649 run #2 (craft2649.img 'eio' mode: volu_size forged
64M -> 128M so the volume lookup for the 96M poison offset would
succeed while the physical read fails).  The mount-time device-size
cross-check (hammer2_ondisk.c:283-290) rejects the inflated volume
header, closing the forged-image route to an in-volume EIO on a valid
mount.  (Note: that check is skipped entirely when DIOCGPART fails on
the backing device -- a hardening gap belonging to hammer2_ondisk.c,
not re-filed under DF-2649.)