Set Page Attributes

Sets the attributes of one or more pages within a linear
memory block previously allocated with Int 31H Fn
0504H.  This function can be used to change a committed page
or a mapped page to an uncommitted page, change an
uncommitted page or a mapped page to a committed page, or
modify the read/write bit and optionally the accessed and
dirty bits on a committed or mapped page.

Call With:

   AX     = 0507H
   ESI    = memory block handle
   EBX    = offset within memory block of page(s) whose
           attributes are to be modified
   ECX    = number of pages
   ES:EDX = selector:offset of a buffer containing page
           attributes, 1 word (16-bits) per page (see Note)

Returns:

   if function successful
   Carry flag= clear

   if function unsuccessful
   Carry flag= set
   AX     = error code
           8001H   unsupported function (16-bit host)
           8002H   invalid state (page in wrong state for
                   request)
           8013H   physical memory unavailable
           8014H   backing store unavailable
           8021H   invalid value (illegal request in bits
                   0-2 of one or more page attribute words)
           8023H   invalid handle (in ESI)
           8025H   invalid linear address (specified range
                   is not within specified block)

   ECX    = number of pages that have been set

Notes:

o  A DPMI 1.0 host that is 16-bit only will not support this
   function.
o  A 16-bit client of a 32-bit DPMI 1.0 host can use this
   function.
o  If EBX is not aligned, it will be rounded down to the
   next lower page boundary.
o  An uncommitted page can be created from:
§  a committed page, by releasing the physical memory or
   backing store allocated to the page;
§  a mapped page, by marking it uncommitted; or
   an uncommitted page, by doing nothing.


o  A committed page can be created from:
§  an uncommitted page or mapped page, by allocating
   physical memory or backing store (with undefined, or
   zero-filled contents) for the page; or
§  a committed page, by doing nothing (page contents
   unmodified).

o  The attribute word (16-bits) specified for a page has the
    following format (bits 3-6 are only relevant if page is
   being created committed or its attributes are being
   modified, i.e. the value in bits 0-2 of the page
   attribute is 1 or 3):

   Bits      Significance
   0-2       page type (0-7)
             Value  Meaning
             0      create page uncommitted
             1      create page committed
             2      not allowed
             3      modify attributes without changing page
   type
             4-7    not allowed
   3         0 = page is read-only
             1 = page is read/write
   4         0 = don't modify accessed/dirty bits for page
             1 = set accessed/dirty bits as specified in
   bits 5-6
   5         0 = mark page as not accessed (if bit 4=1)
             1 = mark page as accessed (if bit 4=1)
   6         0 = mark page as not dirty (if bit 4=1)
             1 = mark page as dirty (if bit 4=1)
   7-15      reserved, should be zero

o  This function, and the optional Map Device and Map
   Conventional Memory functions (Int 31H Functions 0508H
   and 0509H), are the only means of changing the type of a
   page within an existing memory block.
o  The page read/write bit, and optionally the accessed and
   dirty bits, can be modified on an existing committed or
   mapped page, or on a committed page when it is initially
   created from an uncommitted page or a mapped page.
   However, the accessed and dirty bits are ignored if the
   host does not support the Page Accessed/Dirty capability.
   See Int 31H Fn 0401H.

o  Visible page faults (page faults that can be serviced by
   a client-installed exception handler) can only occur for
   uncommitted pages or read-only pages (for definitions of
   transparent page fault and visible page fault, see
   Appendix A: Glossary).