Allocate Linear Memory Block

Allocates a block of page-aligned linear address space.  The
base address of the block may be specified by the client,
and pages within the block may be committed or uncommitted.

Call With:

   AX     = 0504H
   EBX    = desired page-aligned linear address of memory
           block,
   or zero if linear address unspecified
   ECX    = size of block (bytes, must be nonzero)
   EDX    = flags
           Bit    Significance
           0      0 = create uncommitted pages
                  1 = create committed pages
           1-31   reserved, should be zero

Returns:

   if function successful
   Carry flag= clear
   EBX    = linear address of memory block
   ESI    = handle for memory block

   if function unsuccessful
   Carry flag= set
   AX     = error code
           8001H   unsupported function (16-bit host)
           8012H   linear memory unavailable
           8013H   physical memory unavailable
           8014H   backing store unavailable
           8016H   handle unavailable
           8021H   invalid value (ECX = 0)
           8025H   invalid linear address (EBX not page
                   aligned)

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  The allocated block is always page-aligned.  If a
   specific linear address is not requested (EBX = 0), the
   DPMI host allocates the memory block at any available
   page-aligned linear address.  If a specific linear
   address is requested (EBX nonzero), the host either
   allocates the block at the specified address or returns
   error code 8012H (linear memory unavailable).

o  Int 31H Fn 0501H, which can also be used to
   allocate linear memory blocks, does not necessarily
   page-align its blocks and does not have the ability to
   create uncommitted pages or allocate a block at a
   specific linear address.