DF2770 A: full read rv=45 errno=0 ctrl=0x40 (expect 0x40) bytes1..4=02 2b 00 00
DF2770 B: faulting read(2) rv=1 errno=0 (Undefined error: 0)
DF2770 B: byte0=0x40 (0x40=event byte copied before EFAULT swallow; 0xAA=nothing copied)