DF-3232 control — stock geometry (fs_fragshift=3), identical trigger
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$ newfs -b 8192 -f 1024 /dev/vn1 ; mount -t ufs /dev/vn1 /mnt.ctl
$ dd if=/dev/zero of=/mnt.ctl/victim bs=8192 count=1 ; chmod 666 /mnt.ctl/victim
$ su -m maxx -c "/tmp/trig3232 /mnt.ctl/victim"
[*] trigger: uid=1001 file=/mnt.ctl/victim (open+ftruncate(0)+sync)
[*] survived ftruncate+sync
CONTROL_SURVIVED
-rw-rw-rw-  1 root wheel 0 Sep  8 23:57 /mnt.ctl/victim
umount + vnconfig -u clean.