Manual Pages for UNIX Operating System command usage for man mt-streams

Kernel Functions for Drivers                       mt-streams(9F)



NAME
     mt-streams - STREAMS multithreading

SYNOPSIS
     #include 


INTERFACE LEVEL
     Solaris DDI specific (Solaris DDI).

DESCRIPTION
     STREAMS drivers configure the degree  of  concurrency  using
     the  cb_flag field in the cb_ops structure (see cb_ops(9S)).
     The corresponding field for STREAMS modules is the f_flag in
     the fmodsw structure.


     For the purpose of  restricting  and  controlling  the  con-
     currency in drivers/modules, we define the concepts of inner
     and outer perimeters.  A  driver/module  can  be  configured
     either  to  have  no perimeters, to have only an inner or an
     outer perimeter, or to have both an inner and an outer  per-
     imeter.  Each perimeter acts as a readers-writers lock, that
     is, there can be multiple concurrent  readers  or  a  single
     writer.  Thus,  each  perimeter can be entered in two modes:
     shared (reader) or exclusive (writer). The mode  depends  on
     the  perimeter  configuration  and  can be different for the
     different  STREAMS  entry  points  (  open(9E),   close(9E),
     put(9E), or srv(9E)).


     The concurrency for the different entry  points  is  (unless
     specified  otherwise)  to enter with exclusive access at the
     inner perimeter (if present) and shared access at the  outer
     perimeter (if present).


     The perimeter configuration consists of  flags  that  define
     the  presence and scope of the inner perimeter, the presence
     of the outer perimeter (which can only have one scope),  and
     flags  that modify the default concurrency for the different
     entry points.


     All MT safe modules/drivers specify the D_MP flag.

  Inner Perimeter Flags
     The inner perimeter presence and scope are controlled by the
     mutually exclusive flags:

     D_MTPERQ             The module/driver has an inner  perime-
                          ter around each queue.



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Kernel Functions for Drivers                       mt-streams(9F)



     D_MTQPAIR            The module/driver has an inner  perime-
                          ter  around  each  read/write  pair  of
                          queues.


     D_MTPERMOD           The module/driver has an inner  perime-
                          ter     that     encloses    all    the
                          module's/driver's queues.


     None of the above    The module/driver has no inner  perime-
                          ter.


  Outer Perimeter Flags
     The outer perimeter presence is configured using:

     D_MTOUTPERIM    In addition  to  any  inner  perimeter,  the
                     module/driver  has  an  outer perimeter that
                     encloses all the  module's/driver's  queues.
                     This can be combined with all the inner per-
                     imeter options except D_MTPERMOD.



     Note that acquiring exclusive access at the outer  perimeter
     (that  is,  using qwriter(9F) with the PERIM_OUTER flag) can
     incur significant performance penalties, which grow linearly
     with the number of open instances of the module or driver in
     the system.


     The default concurrency can be modified using:

     D_MTPUTSHARED    This flag  modifies  the  default  behavior
                      when  put(9E) procedure are invoked so that
                      the  inner  perimeter  is  entered   shared
                      instead of exclusively.


     D_MTOCEXCL       This flag  modifies  the  default  behavior
                      when  open(9E) and close(9E) procedures are
                      invoked so the outer perimeter  is  entered
                      exclusively instead of shared.

                      Note that drivers and  modules  using  this
                      flag  can  cause significant system perfor-
                      mance degradation  during  stream  open  or
                      close  when many instances of the driver or
                      module are in use simultaneously. For  this
                      reason,  use  of  this flag is discouraged.
                      Instead, since open(9E) and close(9E)  both



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Kernel Functions for Drivers                       mt-streams(9F)



                      execute  with  user context, developers are
                      encouraged to use traditional  synchroniza-
                      tion  routines  such  as cv_wait_sig(9F) to
                      coordinate with other open instances of the
                      module or driver.



     The module/driver can use qwait(9F) or  qwait_sig()  in  the
     open(9E)  and close(9E) procedures if it needs to wait "out-
     side" the perimeters.


     The module/driver can use qwriter(9F) to upgrade the  access
     at the inner or outer perimeter from shared to exclusive.


     The use and semantics of  qprocson()  and  qprocsoff(9F)  is
     independent of the inner and outer perimeters.

SEE ALSO
     close(9E),  open(9E),   put(9E),   srv(9E),   qprocsoff(9F),
     qprocson(9F), qwait(9F), qwriter(9F), cb_ops(9S)


     STREAMS Programming Guide


     Writing Device Drivers


























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