Index for Section 9r

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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
  map Specifies the address map associated with an individual process.

  start
      Specifies the starting address of an address range. Typically, this is
      the address of the user's buffer where the DMA operation occurs.

  end Specifies the ending address of a consecutive range of addresses
      beginning with the start argument.

  access_type
      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:

      VM_PROT_NONE
	      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.

      VM_PROT_READ
	      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.

      VM_PROT_WRITE
	      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.

      VM_PROT_WRITE
	      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 running 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)

Index for Section 9r

Alphabetical listing for V

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