Programming Interface Information: This information is NOT intended to be used as Programming Interfaces of z/VM.

#### EASIT

Prolog

Control Block Contents
EASIT DSECT

Storage Layout

Cross Reference (Contains links to field and bit definitions)

#### 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-Identification
                                      space-identification token.
    0000    0 Address      4 EASASTEO       Bits 1-25 are the ASTE origin...
                                            host logical address.
              ..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

This information is based on z/VM V6R1.0. Last updated on 18 Feb 2010 at 08:37:05 EDT.
Copyright IBM Corporation, 1990, 2008