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contig_malloc(9r)
NAME
  contig_malloc - General: Allocates physically contiguous memory

SYNOPSIS
  #include <sys/malloc.h>


  void * contig_malloc(
	  u_long size,
	  u_long alignment,
	  u_long addrlimit,
	  int type,
	  int flag );

ARGUMENTS
  size
      Specifies the size of the memory (in bytes) to allocate.

  alignment
      Specifies the alignment of the memory to be allocated. For example, for
      a 256-byte alignment, you should pass the value 256. A 0 (zero) value
      means there is no alignment requirement.

  addrlimit
      Specifies that the address of all the allocated memory should be less
      than or equal to this address. A 0 (zero) value means that there is no
      address limit requirement.

  type
      Specifies the purpose for which the memory is being allocated (or
      freed). The memory type constants are defined in the file
      /usr/sys/include/sys/malloc.h. Examples of memory type constants are
      M_DEVBUF (device driver memory), M_KTABLE (kernel table memory),
      M_RTABLE (routing tables memory), and so forth.

  flag
      Specifies one of the following flags defined in
      /usr/sys/include/sys/malloc.h:

      M_ZERO  Signifies that contig_malloc should zero the allocated memory.

      M_WAITOK
	      Signifies that contig_malloc can block.

      M_NOWAIT
	      Signifies that contig_malloc cannot block.





DESCRIPTION
  The contig_malloc routine allocates physically contiguous memory during the
  boot process (before single-user mode). The routine carves out an area of
  physically contiguous memory from a contiguous memory buffer and allocates
  memory from this buffer with proper alignment. The call to contig_malloc is
  the same for statically or dynamically configured drivers. However, the
  point or points in time in which the statically or dynamically configured
  driver requests the memory differ.

  A statically configured driver typically needs to call contig_malloc only
  before single-user mode. In this case, contig_malloc obtains the memory
  from the contiguous memory buffer. When a statically configured driver
  frees this physically contiguous memory (by calling the contig_free
  routine), the memory is returned to the virtual memory subsystem.

  A dynamically configured driver typically needs physically contiguous
  memory after single-user mode. As stated previously, contig_malloc carves
  out an area of physically contiguous memory from a contiguous memory buffer
  before single-user mode. Thus, this memory would not be available to the
  dynamically configured driver after single-user mode. To solve this
  problem, a dynamically configured driver calls contig_malloc by defining
  the CMA_Option attribute in the sysconfigtab file fragment.

  The cma_dd subsystem calls contig_malloc on behalf of dynamically
  configured device drivers and obtains the memory allocation size (and other
  information) from the CMA_Option attribute field. In this case,
  contig_malloc allocates physically contiguous memory from the contiguous
  memory buffer and places it in a saved memory pool. When a dynamically
  configured driver needs to call contig_malloc after single-user mode, the
  physically contiguous memory comes from this saved memory pool. When a
  dynamically configured driver frees this physically contiguous memory (by
  calling the contig_free routine), the memory is returned to the saved
  memory pool (not to the virtual memory subsystem). Thus, this physically
  contiguous memory is available to the dynamically configured driver upon
  subsequent reload requests that occur after single-user mode.

RETURN VALUES
  Upon successful completion, contig_malloc returns a pointer to the
  allocated memory. If contig_malloc cannot allocate the requested memory, it
  returns a null pointer.

SEE ALSO
  Routines: contig_free(9r)

Index for Section 9

Alphabetical listing for C

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