EASIT Back to Index page
Control Block Contents 
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
 DESCRIPTION: External-Address-Space-Identification
 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 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 6.3.0 Last updated on 22 May 2013 at 13:54:23 EDT.
Copyright IBM Corporation, 1990, 2013