[root@dfbsd ~]# /tmp/mirror_poc /mnt/f1 btype0
issuing HAMMERIOC_MIRROR_WRITE mode=btype0 size=80...
(ssh session died; guest dropped to ddb)
--- serial console (vm.sh log) ---
panic: assertion "elm->base.btype != 0" failed in hammer_btree_insert at /usr/src/sys/vfs/hammer/hammer_btree.c:816
cpuid = 0
Trace beginning at frame 0xfffff80118aa8138
hammer_btree_insert() at hammer_btree_insert+0x2d9 0xffffffff8092a9c9
hammer_create_at_cursor() at hammer_create_at_cursor+0x1cf 0xffffffff809438cf
hammer_ioc_mirror_write() at hammer_ioc_mirror_write+0x3f8 0xffffffff809402d8
hammer_ioctl() at hammer_ioctl+0xebe 0xffffffff8093ecce
hammer_vop_ioctl() at hammer_vop_ioctl+0x48 0xffffffff80958978
Debugger("panic")
CPU0 stopping CPUs: 0x0000003e
 stopped
Stopped at      Debugger+0x7c:  movb    $0,0xbdaf09(%rip)
db>
(vm.sh status => down)