===DF-2456: production fdcpio, FD_FORMAT nsecs=255===
$ sysctl "kern.dfhwgo=fd_form 255"
dfhw: PRODUCTION fdcpio moved 1020 bytes for nsecs=255 (4*1020); the formb
idfields region holds only 144 bytes; canary bytes captured from past the
object: 876
dfhw: first captured 0x66 (kmalloc canary fill) at stream index 144; first
0x67 at -1 -- bytes from past the fd_formb heap object were delivered to
the FDC data port
dfhw: sample [144..175]:
   66 66 66 66 66 66 66 66 66 66 66 66 66 66 66 66 66 66 66 66 66 66 66 66
   66 66 66 66 66 66 66 66
(first OOB byte EXACTLY at index 144 = 36 sectors * 4 bytes: the math is
exact; 876 bytes past the fd_formb heap object streamed to the FDC port)

===control nsecs=36 (the legal maximum, FD_MAX_NSEC)===
dfhw: PRODUCTION fdcpio moved 144 bytes for nsecs=36 (4*144); the formb
idfields region holds only 144 bytes; canary bytes captured from past the
object: 0