BITMP | Back to Index page

| Prolog Control Block Contents BITMP 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.

BITMP Prolog | Top of page

     NAME       : HCPBITMP
     DESCRIPTION: Bit Map Control Block
     DSECT      : BITMP
     FUNCTION   : The Bit Map Control Block contains fields that control
                  access to the bits, pointers to the bits, and other
                  useful stuff.
     LOCATED BY : R2 at entry to HCPBIT routines points to a full
                  word that points to the BITMP.
     CREATED BY : HCPBIT
     DELETED BY : HCPBITRL
     REFERENCES : None
     SERIALIZED : Changes to the contents of bit maps need not be done
                  under the control of the BITMP lock, because
                  Compare-and-Swap is used to change the bits and the
                  pointers to the bits.  However, if serialization is
                  needed, the users of the bit maps should call the
                  HCPBIT entry points AS, AX, RS, RX, SX, etc., which
                  call the analogous HCPLCK entry points for control
                  over the BITMP lock.
     RELOCATION CONSIDERATIONS : This control block is relocated as part of a live
                  guest relocation (LGR).  The bits and fields that
                  need to be relocated are defined in the
                  corresponding LGRBITMP COPY file.  Whenever changes
                  are made to this control block, consideration must
                  be given to any effects these changes will have on
                  a relocation.  If any new fields or bits are
                  defined, they may need to be relocated.  If
                  existing bits or fields are changed, corresponding
                  modifications may be required in the LGR version of
                  this control block.  Consider also the effects of
                  these changes on a relocation involving a back-level
                  release of CP.

BITMP Control Block Content | Top of page

     BITMP DSECT
    Top of page

    Hex   Dec Type/Val   Lng Label (dup)    Comments
    ---- ---- --------- ---- -------------- --------
    0000    0 Structure      BITMP          Bit Map Control Block
          This portion of the BITMP is fixed length.  The final size
          of the BITMP depends on how many pointers are actually
          stored at BITMPPTR.
              00000000       BITMPFXD       * Fixed portion of the BITMP
    0000    0 Dbl-Word     8 BITMPLCK (3)   The BITMP lock
    0018   24 Signed       4 BITMPMAX       The max bit number allowed
    001C   28 Signed       4 BITMPPGS       How many pointers at BITMPPTR
              00000020       BITMPFSZ       *-BITMP Size of fixed portion of
                                            BITMP expressed in bytes.
    0020   32 Address      4 BITMPPTR (0)   Start of variable length data.
                                            Pointers to pages of bits. The
                                            upper bound of the subscript for
                                            this array is contained in
                                            BITMPPGS.

BITMP Storage Layout | Top of page

    *** BITMP - Bit Map Control Block
    *
    *     +-------------------------------------------------------+
    *   0 |                                                       |
    *     =                       BITMPLCK                        =
    *     |                                                       |
    *     +---------------------------+---------------------------+
    *  18 |         BITMPMAX          |         BITMPPGS          |
    *     +---------------------------+---------------------------+
    *
    *** BITMP - Bit Map Control Block

BITMP Cross Reference | Top of page

    Symbol         Dspl Value
    -------------- ---- -----
    BITMPFSZ       001C 00000020
    BITMPFXD       0000 00000000
    BITMPLCK       0000
    BITMPMAX       0018
    BITMPPGS       001C
    BITMPPTR       0020

This information is based on z/VM 7.2.0 Last updated on 24 Jun 2020 at 09:27:06 EDT.
Copyright IBM Corporation, 1990, 2020