line disc

[utzoo!decvax!ucbvax!menlo70!sri-unix!MBM at MIT-XX]

From: Michael B McIlrath <MBM at MIT-XX>
Does anyone believe he really understands how the tty line
disciplines are supposed to be used?  Before everyone jumps
to answer, my specific questions are:
1) are the entries in linesw supposed to be called INSTEAD 
   of, or IN ADDITION TO, the "default" ones (i.e., ttymumble)
   by the hardware device handlers?  In particular , most of the
   drivers I have seen that use line disciplines first call the
   linesw entry for ioctl, then  call ttioctl if the linesw entry
   returned non-zero.  The linesw entry itself is usually nullioctl.
   Why?

2) Werent there some special ioctl's (DIOCGET/SET ???? etc) that
   were intended to be specific to the line discipline?  What
   special actions are supposed to be taken when line disciplines
   are changed?  

--mike
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