EASIT

EASIT Prolog

 Name       : HCPEASIT
 Description: External-Address-Space-Identification
              Token
 DSECT      : EASIT
 Function   : This DSECT maps an e-ASIT, which is CP's external
              identification of an address space, and a guest's
              identification of a host address space.
 Located by : Any task accepting an e-ASIT from a guest, or
              providing one to a guest.
 Created by : HCPSITIE when translating an i-ASIT into an e-ASIT.
 Deleted by : Any task which no longer needs the representation.
 Notes      : An e-ASIT is an eight-byte token, doubleword aligned,
              and serves as an external representation of an
              address space.  In external documentation, "ASIT" is
              used to designate an e-ASIT.  An e-ASIT is given to
              guests to represent an address space, and is
              guaranteed to be a system-wide unique token, and
              unique for the life of the current system IPL.  When
              referring to the same address space, the same token
              is given to different guests.  A test for equality
              can therefore be used to see if two e-ASITs represent
              the same address space.  Since an e-ASIT can also be
              received from guests, it must also be "verifiable".
              That is, CP must be able to reliably decide when a
              supposed e-ASIT is a legal token designating an
              existing address space.

EASIT Control Block Content

EASIT DSECT

Hex   Dec Type/Val   Lng Label (dup)    Comments
---- ---- --------- ---- -------------- --------
0000    0 Structure      EASIT          External-Address-Space-Identifica
                                        tion
     space-identification token.
0000    0 Address      4 EASASTEO       Bits 1-25 are the ASTE origin
          ..11 1111      EASASTOB       X'8000003F' Mask used to check
                                        for invalid bits in EASASTEO
                                        field. Bits 0 and 26-32 are
                                        unused and will be zeros when
                                        generated by CP, and must be
                                        zeros when generated by a guest.
0004    4 Signed       4 EASSCRSN       E-ASIT space creation sequence
                                        number.
          00000008       EASLEN         *-EASIT Length in bytes of an
                                        e-ASIT
          00000001       EASSIZE        (EASLEN+7)/8 Size in doublewords
                                        of an e-ASIT

EASIT Storage Layout

          
*** EASIT - External-Address-Space-Identification
*
*     +---------------------------+---------------------------+
*   0 |         EASASTEO          |         EASSCRSN          |
*     +---------------------------+---------------------------+
*   8
*
*** EASIT - External-Address-Space-Identification

EASIT Cross Reference

Symbol         Dspl Value
-------------- ---- -----
EASASTEO       0000
EASASTOB       0000 3F
EASLEN         0004 00000008
EASSCRSN       0004
EASSIZE        0004 00000001