STREAMS putmsg of M_PCPROTO

[Jonathan West]

My understanding is that priority messages bypass flow control,
and a M_PCPROTO message can carry many M_DATA blocks following 
the initial M_PCPROTO block.  If this is correct, how can STREAMS
defend against a bad user process which continuously sends large
M_PCPROTO messages downstream?  I believe the upstream case is handled
by the stream head discarding them.  Thanks!