EASIT | Back to Index page

| Prolog Control Block Contents EASIT DSECT Storage Layout Cross Reference (Contains links to field and bit definitions) |
Programming Interface Information: This information is NOT intended to be used as Programming Interfaces of z/VM.

EASIT Prolog | Top of page

     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.
     RELOCATION CONSIDERATIONS : None
     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 | Top of page

     EASIT DSECT
    Top of page

    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 | Top of page

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

EASIT Cross Reference | Top of page

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

This information is based on z/VM 7.2.0 Last updated on 24 Jun 2020 at 09:28:02 EDT.
Copyright IBM Corporation, 1990, 2020