vm_map_pageable(9r)													       vm_map_pageable(9r)

NAME

       vm_map_pageable - General: Sets pageability of the specified address range

SYNOPSIS

       kern_return_t vm_map_pageable(
	       vm_map_t map,
	       vm_offset_t start,
	       vm_offset_t end,
	       vm_prot_t access_type );

ARGUMENTS

       Specifies  the  address	map associated with an individual process.  Specifies the starting address of an address range. Typically, this is
       the address of the user's buffer where the DMA operation occurs.  Specifies the ending address of a consecutive range of  addresses  begin-
       ning  with  the start argument.	Specifies the access mode to be set for memory specified by the start and end arguments.  You can set this
       argument to VM_PROT_NONE or to the bitwise inclusive OR of the protection bits VM_PROT_READ and VM_PROT_WRITE. These bits  are  defined	in
       the  file  <mach/vm_prot.h>  and have the following meanings: Modifies the memory attributes so that the specified range of addresses is no
       longer locked. This should be done after the DMA operation has completed.  Verifies that the specifed range of addresses is readable by the
       specified  process.  If	so,  the  range of addresses is locked in memory to remain stable throughout the DMA operation.  Verifies that the
       specifed range of addresses is writable by the specified process. If so, the range of addresses	is  locked  in	memory	to  remain  stable
       throughout  the DMA operation.  Verifies that the specifed range of addresses is readable and writable by the specified process. If so, the
       range of addresses is locked in memory to remain stable throughout the DMA operation.

DESCRIPTION

       The vm_map_pageable routine ensures that the address range you specified in the start and end arguments is accessible. If the address range
       is accessible by the specified process, the memory associated with this address range will have its locked attributes modified as specified
       by the access_type argument. A kernel module can call this routine prior to performing a DMA operation to ensure that: The  currently  run-
       ning  process  has  read  or  write  access  permission to the user's buffer The memory representing the user's buffer is locked so that it
       remains available throughout the DMA operation.

NOTES

       This routine may block in the kernel. Therefore, you should release all locks and lower the SPL before calling vm_map_pageable.	 When  the
       routine returns, you should relock the data and check the data integrity.

RETURN VALUES

       Upon  successful  completion,  the vm_map_pageable routine returns the value 0 (zero). Otherwise, it returns a nonzero value to indicate an
       error.

EXAMPLE

       The following code fragment shows how the vm_map_pageable routine ensures that the user's buffer is accessible to cause	the  corresponding
       memory to be locked:

	  if (vm_map_pageable(current_task()->map,
		  trunc_page(bp->b_un.b_addr),
		  round_page(bp->b_un.b_addr + (int)bp->b_bcount),
		  (bp->b_flags == B_READ ? VM_PROT_READ : VM_PROT_WRITE))) { /***************************************************
	* Here you implement the code to perform the	  *
	* actual DMA operation.  Upon conclusion of the   *
	* DMA operation, add the following code to	  *
	* release the locked attribute. 		  *
	***************************************************/

	       if (vm_map_pageable(current_task()->map,
		       trunc_page(bp->b_un.b_addr),
		       round_page(bp->b_un.b_addr + (int)bp->b_bcount),
		       VM_PROT_NONE)) {

SEE ALSO

       Routines: current_task(9r), round_page(9r), trunc_page(9r)

															       vm_map_pageable(9r)