IASIT 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.

  IASIT Prolog Top of page
 DESCRIPTION: Internal-Address-Space-Identification
 FUNCTION   : This DSECT maps an i-ASIT, which is CP's internal
              identification of an address space.
 LOCATED BY : Any task needing an identification of an address
              space.  Some important fields which contain i-ASITs
              RSANASIT i-ASIT for "null" address space.
 CREATED BY : HCPSIT%I when translating various representations of
              address spaces into i-ASITs.
 DELETED BY : Any task which no longer needs the representation.
 NOTES      :
 An i-ASIT is an eight-byte token, doubleword aligned, and
 serves as a task's internal representation of a particular
 address space.  An i-ASIT contains information designating
 which address space, information defining the task's
 "capability" to access the address space, and information
 defining the method of translating addresses for that
 task.  Since it contains more information than just what
 is necessary to identify an address space, an i-ASIT
 cannot be directly compared to another i-ASIT to determine
 if the same space is designated.  A service routine (as
 provided by the HCPCMPIA macro) must be used for i-ASIT
 comparison purposes.
 The capabilities represented in an i-ASIT are the
   - r-access vs. i-access
   - Read/write vs. read/only permission
   - For guest instruction-stream references, whether
     guest prefixing, guest low-address protection,
     and guest fetch-protection override apply.
 Translation of a guest real address into a host real
 address is affected by whether or not the address space is
 the user's base address space, and whether or not the
 user's reference is a primary-space or secondary-space
 reference.  Prefixing, low-address protection, and
 fetch-protection override apply only when the space is the
 base, and when the access is a primary-space or
 secondary-space reference.
 An i-ASIT must be certified before it can be used for any
 purposes.  A certified i-ASIT is one that meets the
 following criteria:
    - The ASTE sequence number in the i-ASIT matches
      the ASTE sequence number in the ASTE (i- or r-access)
    - ASCSEQNO <= ASITSN <= ASTSN          (r-access)
 The i-ASIT certification function is provided by either
 the HCPASMCI entry point or the HCPACERT macro (to be used
 only in cases where performance is a major concern, or the
 routine cannot call another routine which uses PFXTMPSV).
 Other services which process i-ASITS, such as HCPCMPIA
 and HCPCHCR7, handle certification of i-ASITs internally.
  IASIT Control Block Content Top of page

 IASIT DSECT Top of page
Hex Dec Type/Val Lng Label (dup) Comments ---- ---- --------- ---- -------------- -------- 0000 0 Structure IASIT Internal-Address-Space-Identification 0000 0 Address 4 IASASTEO (0) Bits 1-25 are the ASTE origin... host logical address. NOTE: This field may ONLY be used in a certified i-ASIT, otherwise, it may point to an ASTE which has no relation to the i-ASIT. 00FFFFC0 IASASTOM X'7FFFFFC0' Mask to apply to IASASTEO to isolate ASTE origin. .... ..1. IASREADM X'00000002' Mask for read-only bit .... ...1 IASFPRVM X'00000001' Mask for force-private-space bit 0000 0 Bitstring 1 * (3) First 3 bytes are ASTE origin 0003 3 Bitstring 1 IASFLAGS Authorization/capability flags .... .1.. IASRACC X'04' IASRACC When set, task has r-access to the address space. .... ..1. IASREAD X'02' IASREAD When set, task has read-only access to space. .... ...1 IASFPRIV X'01' IASFPRIV Force-Private-Space bit When set, guest prefixing, low-address protection, and fetch-protection override do not apply. When not set, they do apply. Bits 0, 26-28, and 32 are unused and will be zeros. 0004 4 Signed 4 IASASTSN I-ASIT ASTE sequence number. It is compared with ASTE sequence number in ASTE. 00000008 IASLEN *-IASIT Length in bytes of an i-ASIT 00000001 IASSIZE (IASLEN+7)/8 Size in doublewords of an i-ASIT
  IASIT Storage Layout Top of page
*** IASIT - Internal-Address-Space-Identification
*     +--------------------+------+---------------------------+
*   0 |////////////////////|:FLAGS|         IASASTSN          |
*     +--------------------+------+---------------------------+
*   8
*** IASIT - Internal-Address-Space-Identification
  IASIT Cross Reference Top of page
Symbol         Dspl Value
-------------- ---- -----
IASASTEO       0000
IASASTOM       0000 00FFFFC0
IASASTSN       0004
IASFLAGS       0003
IASFPRIV       0003 01
IASFPRVM       0000 01
IASLEN         0004 00000008
IASRACC        0003 04
IASREAD        0003 02
IASREADM       0000 02
IASSIZE        0004 00000001
This information is based on z/VM 6.3.0 Last updated on 22 May 2013 at 13:54:37 EDT.
Copyright IBM Corporation, 1990, 2013