path: root/MdePkg/Library/UefiDevicePathLib/DevicePathUtilities.c

/** @file
  Device Path services. The thing to remember is device paths are built out of
  nodes. The device path is terminated by an end node that is length
  sizeof(EFI_DEVICE_PATH_PROTOCOL). That would be why there is sizeof(EFI_DEVICE_PATH_PROTOCOL)
  all over this file.

  The only place where multi-instance device paths are supported is in
  environment varibles. Multi-instance device paths should never be placed
  on a Handle.

  Copyright (c) 2006 - 2016, Intel Corporation. All rights reserved.<BR>
  This program and the accompanying materials                          
  are licensed and made available under the terms and conditions of the BSD License         
  which accompanies this distribution.  The full text of the license may be found at        
  http://opensource.org/licenses/bsd-license.php.                                            

  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,                     
  WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.             

**/

#include "UefiDevicePathLib.h"

//
// Template for an end-of-device path node.
//
GLOBAL_REMOVE_IF_UNREFERENCED CONST EFI_DEVICE_PATH_PROTOCOL  mUefiDevicePathLibEndDevicePath = {
  END_DEVICE_PATH_TYPE,
  END_ENTIRE_DEVICE_PATH_SUBTYPE,
  {
    END_DEVICE_PATH_LENGTH,
    0
  }
};

/**
  Determine whether a given device path is valid.
  If DevicePath is NULL, then ASSERT().

  @param  DevicePath  A pointer to a device path data structure.
  @param  MaxSize     The maximum size of the device path data structure.

  @retval TRUE        DevicePath is valid.
  @retval FALSE       The length of any node node in the DevicePath is less
                      than sizeof (EFI_DEVICE_PATH_PROTOCOL).
  @retval FALSE       If MaxSize is not zero, the size of the DevicePath
                      exceeds MaxSize.
  @retval FALSE       If PcdMaximumDevicePathNodeCount is not zero, the node
                      count of the DevicePath exceeds PcdMaximumDevicePathNodeCount.
**/
BOOLEAN
EFIAPI
IsDevicePathValid (
  IN CONST EFI_DEVICE_PATH_PROTOCOL *DevicePath,
  IN       UINTN                    MaxSize
  )
{
  UINTN Count;
  UINTN Size;
  UINTN NodeLength;

  ASSERT (DevicePath != NULL);

  for (Count = 0, Size = 0; !IsDevicePathEnd (DevicePath); DevicePath = NextDevicePathNode (DevicePath)) {
    NodeLength = DevicePathNodeLength (DevicePath);
    if (NodeLength < sizeof (EFI_DEVICE_PATH_PROTOCOL)) {
      return FALSE;
    }

    if (MaxSize > 0) {
      Size += NodeLength;
      if (Size + END_DEVICE_PATH_LENGTH > MaxSize) {
        return FALSE;
      }
    }

    if (PcdGet32 (PcdMaximumDevicePathNodeCount) > 0) {
      Count++;
      if (Count >= PcdGet32 (PcdMaximumDevicePathNodeCount)) {
        return FALSE;
      }
    }
  }

  //
  // Only return TRUE when the End Device Path node is valid.
  //
  return (BOOLEAN) (DevicePathNodeLength (DevicePath) == END_DEVICE_PATH_LENGTH);
}


/**
  Returns the Type field of a device path node.

  Returns the Type field of the device path node specified by Node.

  If Node is NULL, then ASSERT().

  @param  Node      A pointer to a device path node data structure.

  @return The Type field of the device path node specified by Node.

**/
UINT8
EFIAPI
DevicePathType (
  IN CONST VOID  *Node
  )
{
  ASSERT (Node != NULL);
  return ((EFI_DEVICE_PATH_PROTOCOL *)(Node))->Type;
}

/**
  Returns the SubType field of a device path node.

  Returns the SubType field of the device path node specified by Node.

  If Node is NULL, then ASSERT().

  @param  Node      A pointer to a device path node data structure.

  @return The SubType field of the device path node specified by Node.

**/
UINT8
EFIAPI
DevicePathSubType (
  IN CONST VOID  *Node
  )
{
  ASSERT (Node != NULL);
  return ((EFI_DEVICE_PATH_PROTOCOL *)(Node))->SubType;
}

/**
  Returns the 16-bit Length field of a device path node.

  Returns the 16-bit Length field of the device path node specified by Node.  
  Node is not required to be aligned on a 16-bit boundary, so it is recommended
  that a function such as ReadUnaligned16() be used to extract the contents of 
  the Length field.

  If Node is NULL, then ASSERT().

  @param  Node      A pointer to a device path node data structure.

  @return The 16-bit Length field of the device path node specified by Node.

**/
UINTN
EFIAPI
DevicePathNodeLength (
  IN CONST VOID  *Node
  )
{
  ASSERT (Node != NULL);
  return ReadUnaligned16 ((UINT16 *)&((EFI_DEVICE_PATH_PROTOCOL *)(Node))->Length[0]);
}

/**
  Returns a pointer to the next node in a device path.

  Returns a pointer to the device path node that follows the device path node 
  specified by Node.

  If Node is NULL, then ASSERT().

  @param  Node      A pointer to a device path node data structure.

  @return a pointer to the device path node that follows the device path node 
  specified by Node.

**/
EFI_DEVICE_PATH_PROTOCOL *
EFIAPI
NextDevicePathNode (
  IN CONST VOID  *Node
  )
{
  ASSERT (Node != NULL);
  return (EFI_DEVICE_PATH_PROTOCOL *)((UINT8 *)(Node) + DevicePathNodeLength(Node));
}

/**
  Determines if a device path node is an end node of a device path.
  This includes nodes that are the end of a device path instance and nodes that 
  are the end of an entire device path.

  Determines if the device path node specified by Node is an end node of a device path.  
  This includes nodes that are the end of a device path instance and nodes that are the 
  end of an entire device path.  If Node represents an end node of a device path, 
  then TRUE is returned.  Otherwise, FALSE is returned.

  If Node is NULL, then ASSERT().

  @param  Node      A pointer to a device path node data structure.

  @retval TRUE      The device path node specified by Node is an end node of a 
                    device path.
  @retval FALSE     The device path node specified by Node is not an end node of 
                    a device path.
  
**/
BOOLEAN
EFIAPI
IsDevicePathEndType (
  IN CONST VOID  *Node
  )
{
  ASSERT (Node != NULL);
  return (BOOLEAN) (DevicePathType (Node) == END_DEVICE_PATH_TYPE);
}

/**
  Determines if a device path node is an end node of an entire device path.

  Determines if a device path node specified by Node is an end node of an entire 
  device path. If Node represents the end of an entire device path, then TRUE is 
  returned.  Otherwise, FALSE is returned.

  If Node is NULL, then ASSERT().

  @param  Node      A pointer to a device path node data structure.

  @retval TRUE      The device path node specified by Node is the end of an entire 
                    device path.
  @retval FALSE     The device path node specified by Node is not the end of an 
                    entire device path.

**/
BOOLEAN
EFIAPI
IsDevicePathEnd (
  IN CONST VOID  *Node
  )
{
  ASSERT (Node != NULL);
  return (BOOLEAN) (IsDevicePathEndType (Node) && DevicePathSubType(Node) == END_ENTIRE_DEVICE_PATH_SUBTYPE);
}

/**
  Determines if a device path node is an end node of a device path instance.

  Determines if a device path node specified by Node is an end node of a device 
  path instance. If Node represents the end of a device path instance, then TRUE 
  is returned.  Otherwise, FALSE is returned.

  If Node is NULL, then ASSERT().

  @param  Node      A pointer to a device path node data structure.

  @retval TRUE      The device path node specified by Node is the end of a device 
                    path instance.
  @retval FALSE     The device path node specified by Node is not the end of a 
                    device path instance.

**/
BOOLEAN
EFIAPI
IsDevicePathEndInstance (
  IN CONST VOID  *Node
  )
{
  ASSERT (Node != NULL);
  return (BOOLEAN) (IsDevicePathEndType (Node) && DevicePathSubType(Node) == END_INSTANCE_DEVICE_PATH_SUBTYPE);
}

/**
  Sets the length, in bytes, of a device path node.

  Sets the length of the device path node specified by Node to the value specified 
  by NodeLength.  NodeLength is returned.  Node is not required to be aligned on 
  a 16-bit boundary, so it is recommended that a function such as WriteUnaligned16()
  be used to set the contents of the Length field.

  If Node is NULL, then ASSERT().
  If NodeLength >= SIZE_64KB, then ASSERT().
  If NodeLength < sizeof (EFI_DEVICE_PATH_PROTOCOL), then ASSERT().

  @param  Node      A pointer to a device path node data structure.
  @param  Length    The length, in bytes, of the device path node.

  @return Length

**/
UINT16
EFIAPI
SetDevicePathNodeLength (
  IN OUT VOID  *Node,
  IN UINTN     Length
  )
{
  ASSERT (Node != NULL);
  ASSERT ((Length >= sizeof (EFI_DEVICE_PATH_PROTOCOL)) && (Length < SIZE_64KB));
  return WriteUnaligned16 ((UINT16 *)&((EFI_DEVICE_PATH_PROTOCOL *)(Node))->Length[0], (UINT16)(Length));
}

/**
  Fills in all the fields of a device path node that is the end of an entire device path.

  Fills in all the fields of a device path node specified by Node so Node represents 
  the end of an entire device path.  The Type field of Node is set to 
  END_DEVICE_PATH_TYPE, the SubType field of Node is set to 
  END_ENTIRE_DEVICE_PATH_SUBTYPE, and the Length field of Node is set to 
  END_DEVICE_PATH_LENGTH.  Node is not required to be aligned on a 16-bit boundary, 
  so it is recommended that a function such as WriteUnaligned16() be used to set 
  the contents of the Length field. 

  If Node is NULL, then ASSERT(). 

  @param  Node      A pointer to a device path node data structure.

**/
VOID
EFIAPI
SetDevicePathEndNode (
  OUT VOID  *Node
  )
{
  ASSERT (Node != NULL);
  CopyMem (Node, &mUefiDevicePathLibEndDevicePath, sizeof (mUefiDevicePathLibEndDevicePath));
}

/**
  Returns the size of a device path in bytes.

  This function returns the size, in bytes, of the device path data structure 
  specified by DevicePath including the end of device path node.
  If DevicePath is NULL or invalid, then 0 is returned.

  @param  DevicePath  A pointer to a device path data structure.

  @retval 0           If DevicePath is NULL or invalid.
  @retval Others      The size of a device path in bytes.

**/
UINTN
EFIAPI
UefiDevicePathLibGetDevicePathSize (
  IN CONST EFI_DEVICE_PATH_PROTOCOL  *DevicePath
  )
{
  CONST EFI_DEVICE_PATH_PROTOCOL  *Start;

  if (DevicePath == NULL) {
    return 0;
  }

  if (!IsDevicePathValid (DevicePath, 0)) {
    return 0;
  }

  //
  // Search for the end of the device path structure
  //
  Start = DevicePath;
  while (!IsDevicePathEnd (DevicePath)) {
    DevicePath = NextDevicePathNode (DevicePath);
  }

  //
  // Compute the size and add back in the size of the end device path structure
  //
  return ((UINTN) DevicePath - (UINTN) Start) + DevicePathNodeLength (DevicePath);
}

/**
  Creates a new copy of an existing device path.

  This function allocates space for a new copy of the device path specified by DevicePath.  
  If DevicePath is NULL, then NULL is returned.  If the memory is successfully 
  allocated, then the contents of DevicePath are copied to the newly allocated 
  buffer, and a pointer to that buffer is returned.  Otherwise, NULL is returned.  
  The memory for the new device path is allocated from EFI boot services memory. 
  It is the responsibility of the caller to free the memory allocated. 
  
  @param  DevicePath    A pointer to a device path data structure.

  @retval NULL          DevicePath is NULL or invalid.
  @retval Others        A pointer to the duplicated device path.
  
**/
EFI_DEVICE_PATH_PROTOCOL *
EFIAPI
UefiDevicePathLibDuplicateDevicePath (
  IN CONST EFI_DEVICE_PATH_PROTOCOL  *DevicePath
  )
{
  UINTN                     Size;

  //
  // Compute the size
  //
  Size = GetDevicePathSize (DevicePath);
  if (Size == 0) {
    return NULL;
  }

  //
  // Allocate space for duplicate device path
  //

  return AllocateCopyPool (Size, DevicePath);
}

/**
  Creates a new device path by appending a second device path to a first device path.

  This function creates a new device path by appending a copy of SecondDevicePath 
  to a copy of FirstDevicePath in a newly allocated buffer.  Only the end-of-device-path 
  device node from SecondDevicePath is retained. The newly created device path is 
  returned. If FirstDevicePath is NULL, then it is ignored, and a duplicate of 
  SecondDevicePath is returned.  If SecondDevicePath is NULL, then it is ignored, 
  and a duplicate of FirstDevicePath is returned. If both FirstDevicePath and 
  SecondDevicePath are NULL, then a copy of an end-of-device-path is returned.  
  
  If there is not enough memory for the newly allocated buffer, then NULL is returned.
  The memory for the new device path is allocated from EFI boot services memory. 
  It is the responsibility of the caller to free the memory allocated.

  @param  FirstDevicePath            A pointer to a device path data structure.
  @param  SecondDevicePath           A pointer to a device path data structure.
  
  @retval NULL      If there is not enough memory for the newly allocated buffer.
  @retval NULL      If FirstDevicePath or SecondDevicePath is invalid.
  @retval Others    A pointer to the new device path if success.
                    Or a copy an end-of-device-path if both FirstDevicePath and SecondDevicePath are NULL.

**/
EFI_DEVICE_PATH_PROTOCOL *
EFIAPI
UefiDevicePathLibAppendDevicePath (
  IN CONST EFI_DEVICE_PATH_PROTOCOL  *FirstDevicePath,  OPTIONAL
  IN CONST EFI_DEVICE_PATH_PROTOCOL  *SecondDevicePath  OPTIONAL
  )
{
  UINTN                     Size;
  UINTN                     Size1;
  UINTN                     Size2;
  EFI_DEVICE_PATH_PROTOCOL  *NewDevicePath;
  EFI_DEVICE_PATH_PROTOCOL  *DevicePath2;

  //
  // If there's only 1 path, just duplicate it.
  //
  if (FirstDevicePath == NULL) {
    return DuplicateDevicePath ((SecondDevicePath != NULL) ? SecondDevicePath : &mUefiDevicePathLibEndDevicePath);
  }

  if (SecondDevicePath == NULL) {
    return DuplicateDevicePath (FirstDevicePath);
  }

  if (!IsDevicePathValid (FirstDevicePath, 0) || !IsDevicePathValid (SecondDevicePath, 0)) {
    return NULL;
  }

  //
  // Allocate space for the combined device path. It only has one end node of
  // length EFI_DEVICE_PATH_PROTOCOL.
  //
  Size1         = GetDevicePathSize (FirstDevicePath);
  Size2         = GetDevicePathSize (SecondDevicePath);
  Size          = Size1 + Size2 - END_DEVICE_PATH_LENGTH;

  NewDevicePath = AllocatePool (Size);

  if (NewDevicePath != NULL) {
    NewDevicePath = CopyMem (NewDevicePath, FirstDevicePath, Size1);
    //
    // Over write FirstDevicePath EndNode and do the copy
    //
    DevicePath2 = (EFI_DEVICE_PATH_PROTOCOL *) ((CHAR8 *) NewDevicePath +
                  (Size1 - END_DEVICE_PATH_LENGTH));
    CopyMem (DevicePath2, SecondDevicePath, Size2);
  }

  return NewDevicePath;
}

/**
  Creates a new path by appending the device node to the device path.

  This function creates a new device path by appending a copy of the device node 
  specified by DevicePathNode to a copy of the device path specified by DevicePath 
  in an allocated buffer. The end-of-device-path device node is moved after the 
  end of the appended device node.
  If DevicePathNode is NULL then a copy of DevicePath is returned.
  If DevicePath is NULL then a copy of DevicePathNode, followed by an end-of-device 
  path device node is returned.
  If both DevicePathNode and DevicePath are NULL then a copy of an end-of-device-path 
  device node is returned.
  If there is not enough memory to allocate space for the new device path, then 
  NULL is returned.  
  The memory is allocated from EFI boot services memory. It is the responsibility 
  of the caller to free the memory allocated.

  @param  DevicePath                 A pointer to a device path data structure.
  @param  DevicePathNode             A pointer to a single device path node.

  @retval NULL      If there is not enough memory for the new device path.
  @retval Others    A pointer to the new device path if success.
                    A copy of DevicePathNode followed by an end-of-device-path node 
                    if both FirstDevicePath and SecondDevicePath are NULL.
                    A copy of an end-of-device-path node if both FirstDevicePath 
                    and SecondDevicePath are NULL.

**/
EFI_DEVICE_PATH_PROTOCOL *
EFIAPI
UefiDevicePathLibAppendDevicePathNode (
  IN CONST EFI_DEVICE_PATH_PROTOCOL  *DevicePath,     OPTIONAL
  IN CONST EFI_DEVICE_PATH_PROTOCOL  *DevicePathNode  OPTIONAL
  )
{
  EFI_DEVICE_PATH_PROTOCOL  *TempDevicePath;
  EFI_DEVICE_PATH_PROTOCOL  *NextNode;
  EFI_DEVICE_PATH_PROTOCOL  *NewDevicePath;
  UINTN                     NodeLength;

  if (DevicePathNode == NULL) {
    return DuplicateDevicePath ((DevicePath != NULL) ? DevicePath : &mUefiDevicePathLibEndDevicePath);
  }
  //
  // Build a Node that has a terminator on it
  //
  NodeLength = DevicePathNodeLength (DevicePathNode);

  TempDevicePath = AllocatePool (NodeLength + END_DEVICE_PATH_LENGTH);
  if (TempDevicePath == NULL) {
    return NULL;
  }
  TempDevicePath = CopyMem (TempDevicePath, DevicePathNode, NodeLength);
  //
  // Add and end device path node to convert Node to device path
  //
  NextNode = NextDevicePathNode (TempDevicePath);
  SetDevicePathEndNode (NextNode);
  //
  // Append device paths
  //
  NewDevicePath = AppendDevicePath (DevicePath, TempDevicePath);

  FreePool (TempDevicePath);

  return NewDevicePath;
}

/**
  Creates a new device path by appending the specified device path instance to the specified device
  path.
 
  This function creates a new device path by appending a copy of the device path 
  instance specified by DevicePathInstance to a copy of the device path specified 
  by DevicePath in a allocated buffer.
  The end-of-device-path device node is moved after the end of the appended device 
  path instance and a new end-of-device-path-instance node is inserted between. 
  If DevicePath is NULL, then a copy if DevicePathInstance is returned.
  If DevicePathInstance is NULL, then NULL is returned.
  If DevicePath or DevicePathInstance is invalid, then NULL is returned.
  If there is not enough memory to allocate space for the new device path, then 
  NULL is returned.  
  The memory is allocated from EFI boot services memory. It is the responsibility 
  of the caller to free the memory allocated.
  
  @param  DevicePath                 A pointer to a device path data structure.
  @param  DevicePathInstance         A pointer to a device path instance.

  @return A pointer to the new device path.

**/
EFI_DEVICE_PATH_PROTOCOL *
EFIAPI
UefiDevicePathLibAppendDevicePathInstance (
  IN CONST EFI_DEVICE_PATH_PROTOCOL  *DevicePath,        OPTIONAL
  IN CONST EFI_DEVICE_PATH_PROTOCOL  *DevicePathInstance OPTIONAL
  )
{
  EFI_DEVICE_PATH_PROTOCOL  *NewDevicePath;
  EFI_DEVICE_PATH_PROTOCOL  *TempDevicePath;
  UINTN                     SrcSize;
  UINTN                     InstanceSize;

  if (DevicePath == NULL) {
    return DuplicateDevicePath (DevicePathInstance);
  }

  if (DevicePathInstance == NULL) {
    return NULL;
  }

  if (!IsDevicePathValid (DevicePath, 0) || !IsDevicePathValid (DevicePathInstance, 0)) {
    return NULL;
  }

  SrcSize       = GetDevicePathSize (DevicePath);
  InstanceSize  = GetDevicePathSize (DevicePathInstance);

  NewDevicePath = AllocatePool (SrcSize + InstanceSize);
  if (NewDevicePath != NULL) {
    
    TempDevicePath = CopyMem (NewDevicePath, DevicePath, SrcSize);;
 
    while (!IsDevicePathEnd (TempDevicePath)) {
      TempDevicePath = NextDevicePathNode (TempDevicePath);
    }
    
    TempDevicePath->SubType  = END_INSTANCE_DEVICE_PATH_SUBTYPE;
    TempDevicePath           = NextDevicePathNode (TempDevicePath);
    CopyMem (TempDevicePath, DevicePathInstance, InstanceSize);
  }

  return NewDevicePath;
}

/**
  Creates a copy of the current device path instance and returns a pointer to the next device path
  instance.

  This function creates a copy of the current device path instance. It also updates 
  DevicePath to point to the next device path instance in the device path (or NULL 
  if no more) and updates Size to hold the size of the device path instance copy.
  If DevicePath is NULL, then NULL is returned.
  If DevicePath points to a invalid device path, then NULL is returned.
  If there is not enough memory to allocate space for the new device path, then 
  NULL is returned.  
  The memory is allocated from EFI boot services memory. It is the responsibility 
  of the caller to free the memory allocated.
  If Size is NULL, then ASSERT().
 
  @param  DevicePath                 On input, this holds the pointer to the current 
                                     device path instance. On output, this holds 
                                     the pointer to the next device path instance 
                                     or NULL if there are no more device path
                                     instances in the device path pointer to a 
                                     device path data structure.
  @param  Size                       On output, this holds the size of the device 
                                     path instance, in bytes or zero, if DevicePath 
                                     is NULL.

  @return A pointer to the current device path instance.

**/
EFI_DEVICE_PATH_PROTOCOL *
EFIAPI
UefiDevicePathLibGetNextDevicePathInstance (
  IN OUT EFI_DEVICE_PATH_PROTOCOL    **DevicePath,
  OUT UINTN                          *Size
  )
{
  EFI_DEVICE_PATH_PROTOCOL  *DevPath;
  EFI_DEVICE_PATH_PROTOCOL  *ReturnValue;
  UINT8                     Temp;

  ASSERT (Size != NULL);

  if (DevicePath == NULL || *DevicePath == NULL) {
    *Size = 0;
    return NULL;
  }

  if (!IsDevicePathValid (*DevicePath, 0)) {
    return NULL;
  }

  //
  // Find the end of the device path instance
  //
  DevPath = *DevicePath;
  while (!IsDevicePathEndType (DevPath)) {
    DevPath = NextDevicePathNode (DevPath);
  }

  //
  // Compute the size of the device path instance
  //
  *Size = ((UINTN) DevPath - (UINTN) (*DevicePath)) + sizeof (EFI_DEVICE_PATH_PROTOCOL);
 
  //
  // Make a copy and return the device path instance
  //
  Temp              = DevPath->SubType;
  DevPath->SubType  = END_ENTIRE_DEVICE_PATH_SUBTYPE;
  ReturnValue       = DuplicateDevicePath (*DevicePath);
  DevPath->SubType  = Temp;

  //
  // If DevPath is the end of an entire device path, then another instance
  // does not follow, so *DevicePath is set to NULL.
  //
  if (DevicePathSubType (DevPath) == END_ENTIRE_DEVICE_PATH_SUBTYPE) {
    *DevicePath = NULL;
  } else {
    *DevicePath = NextDevicePathNode (DevPath);
  }

  return ReturnValue;
}

/**
  Creates a device node.

  This function creates a new device node in a newly allocated buffer of size 
  NodeLength and initializes the device path node header with NodeType and NodeSubType.  
  The new device path node is returned.
  If NodeLength is smaller than a device path header, then NULL is returned.  
  If there is not enough memory to allocate space for the new device path, then 
  NULL is returned.  
  The memory is allocated from EFI boot services memory. It is the responsibility 
  of the caller to free the memory allocated.

  @param  NodeType                   The device node type for the new device node.
  @param  NodeSubType                The device node sub-type for the new device node.
  @param  NodeLength                 The length of the new device node.

  @return The new device path.

**/
EFI_DEVICE_PATH_PROTOCOL *
EFIAPI
UefiDevicePathLibCreateDeviceNode (
  IN UINT8                           NodeType,
  IN UINT8                           NodeSubType,
  IN UINT16                          NodeLength
  )
{
  EFI_DEVICE_PATH_PROTOCOL      *DevicePath;

  if (NodeLength < sizeof (EFI_DEVICE_PATH_PROTOCOL)) {
    //
    // NodeLength is less than the size of the header.
    //
    return NULL;
  }
 
  DevicePath = AllocateZeroPool (NodeLength);
  if (DevicePath != NULL) {
     DevicePath->Type    = NodeType;
     DevicePath->SubType = NodeSubType;
     SetDevicePathNodeLength (DevicePath, NodeLength);
  }

  return DevicePath;
}

/**
  Determines if a device path is single or multi-instance.

  This function returns TRUE if the device path specified by DevicePath is
  multi-instance.
  Otherwise, FALSE is returned.
  If DevicePath is NULL or invalid, then FALSE is returned.

  @param  DevicePath                 A pointer to a device path data structure.

  @retval  TRUE                      DevicePath is multi-instance.
  @retval  FALSE                     DevicePath is not multi-instance, or DevicePath 
                                     is NULL or invalid.

**/
BOOLEAN
EFIAPI
UefiDevicePathLibIsDevicePathMultiInstance (
  IN CONST EFI_DEVICE_PATH_PROTOCOL  *DevicePath
  )
{
  CONST EFI_DEVICE_PATH_PROTOCOL     *Node;

  if (DevicePath == NULL) {
    return FALSE;
  }

  if (!IsDevicePathValid (DevicePath, 0)) {
    return FALSE;
  }

  Node = DevicePath;
  while (!IsDevicePathEnd (Node)) {
    if (IsDevicePathEndInstance (Node)) {
      return TRUE;
    }

    Node = NextDevicePathNode (Node);
  }

  return FALSE;
}


/**
  Retrieves the device path protocol from a handle.

  This function returns the device path protocol from the handle specified by Handle.  
  If Handle is NULL or Handle does not contain a device path protocol, then NULL 
  is returned.
 
  @param  Handle                     The handle from which to retrieve the device 
                                     path protocol.

  @return The device path protocol from the handle specified by Handle.

**/
EFI_DEVICE_PATH_PROTOCOL *
EFIAPI
DevicePathFromHandle (
  IN EFI_HANDLE                      Handle
  )
{
  EFI_DEVICE_PATH_PROTOCOL  *DevicePath;
  EFI_STATUS                Status;

  Status = gBS->HandleProtocol (
                  Handle,
                  &gEfiDevicePathProtocolGuid,
                  (VOID *) &DevicePath
                  );
  if (EFI_ERROR (Status)) {
    DevicePath = NULL;
  }
  return DevicePath;
}

/**
  Allocates a device path for a file and appends it to an existing device path.

  If Device is a valid device handle that contains a device path protocol, then a device path for
  the file specified by FileName  is allocated and appended to the device path associated with the
  handle Device.  The allocated device path is returned.  If Device is NULL or Device is a handle
  that does not support the device path protocol, then a device path containing a single device
  path node for the file specified by FileName is allocated and returned.
  The memory for the new device path is allocated from EFI boot services memory. It is the responsibility
  of the caller to free the memory allocated.
  
  If FileName is NULL, then ASSERT().
  If FileName is not aligned on a 16-bit boundary, then ASSERT().

  @param  Device                     A pointer to a device handle.  This parameter 
                                     is optional and may be NULL.
  @param  FileName                   A pointer to a Null-terminated Unicode string.

  @return The allocated device path.

**/
EFI_DEVICE_PATH_PROTOCOL *
EFIAPI
FileDevicePath (
  IN EFI_HANDLE                      Device,     OPTIONAL
  IN CONST CHAR16                    *FileName
  )
{
  UINTN                     Size;
  FILEPATH_DEVICE_PATH      *FilePath;
  EFI_DEVICE_PATH_PROTOCOL  *DevicePath;
  EFI_DEVICE_PATH_PROTOCOL  *FileDevicePath;

  DevicePath = NULL;

  Size = StrSize (FileName);
  FileDevicePath = AllocatePool (Size + SIZE_OF_FILEPATH_DEVICE_PATH + END_DEVICE_PATH_LENGTH);
  if (FileDevicePath != NULL) {
    FilePath = (FILEPATH_DEVICE_PATH *) FileDevicePath;
    FilePath->Header.Type    = MEDIA_DEVICE_PATH;
    FilePath->Header.SubType = MEDIA_FILEPATH_DP;
    CopyMem (&FilePath->PathName, FileName, Size);
    SetDevicePathNodeLength (&FilePath->Header, Size + SIZE_OF_FILEPATH_DEVICE_PATH);
    SetDevicePathEndNode (NextDevicePathNode (&FilePath->Header));

    if (Device != NULL) {
      DevicePath = DevicePathFromHandle (Device);
    }

    DevicePath = AppendDevicePath (DevicePath, FileDevicePath);
    FreePool (FileDevicePath);
  }

  return DevicePath;
}