path: root/OvmfPkg/Library/PlatformBdsLib/QemuBootOrder.c

/** @file
  Rewrite the BootOrder NvVar based on QEMU's "bootorder" fw_cfg file.

  Copyright (C) 2012, Red Hat, Inc.

  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 <Library/QemuFwCfgLib.h>
#include <Library/DebugLib.h>
#include <Library/MemoryAllocationLib.h>
#include <Library/GenericBdsLib.h>
#include <Library/UefiBootServicesTableLib.h>
#include <Library/UefiRuntimeServicesTableLib.h>
#include <Library/BaseLib.h>
#include <Library/PrintLib.h>
#include <Protocol/DevicePathToText.h>
#include <Guid/GlobalVariable.h>


/**
  OpenFirmware to UEFI device path translation output buffer size in CHAR16's.
**/
#define TRANSLATION_OUTPUT_SIZE 0x100


/**
  Number of nodes in OpenFirmware device paths that is required and examined.
**/
#define FIXED_OFW_NODES 4


/**
  Simple character classification routines, corresponding to POSIX class names
  and ASCII encoding.
**/
STATIC
BOOLEAN
IsAlnum (
  IN  CHAR8 Chr
  )
{
  return (('0' <= Chr && Chr <= '9') ||
          ('A' <= Chr && Chr <= 'Z') ||
          ('a' <= Chr && Chr <= 'z')
          );
}


STATIC
BOOLEAN
IsDriverNamePunct (
  IN  CHAR8 Chr
  )
{
  return (Chr == ',' ||  Chr == '.' || Chr == '_' ||
          Chr == '+' || Chr == '-'
          );
}


STATIC
BOOLEAN
IsPrintNotDelim (
  IN  CHAR8 Chr
  )
{
  return (32 <= Chr && Chr <= 126 &&
          Chr != '/' && Chr != '@' && Chr != ':');
}


/**
  Utility types and functions.
**/
typedef struct {
  CONST CHAR8 *Ptr; // not necessarily NUL-terminated
  UINTN       Len;  // number of non-NUL characters
} SUBSTRING;


/**

  Check if Substring and String have identical contents.

  The function relies on the restriction that a SUBSTRING cannot have embedded
  NULs either.

  @param[in] Substring  The SUBSTRING input to the comparison.

  @param[in] String     The ASCII string input to the comparison.


  @return  Whether the inputs have identical contents.

**/
STATIC
BOOLEAN
SubstringEq (
  IN  SUBSTRING   Substring,
  IN  CONST CHAR8 *String
  )
{
  UINTN       Pos;
  CONST CHAR8 *Chr;

  Pos = 0;
  Chr = String;

  while (Pos < Substring.Len && Substring.Ptr[Pos] == *Chr) {
    ++Pos;
    ++Chr;
  }

  return (Pos == Substring.Len && *Chr == '\0');
}


/**

  Parse a comma-separated list of hexadecimal integers into the elements of an
  UINT32 array.

  Whitespace, "0x" prefixes, leading or trailing commas, sequences of commas,
  or an empty string are not allowed; they are rejected.

  The function relies on ASCII encoding.

  @param[in]     UnitAddress  The substring to parse.

  @param[out]    Result       The array, allocated by the caller, to receive
                              the parsed values. This parameter may be NULL if
                              NumResults is zero on input.

  @param[in out] NumResults   On input, the number of elements allocated for
                              Result. On output, the number of elements it has
                              taken (or would have taken) to parse the string
                              fully.


  @retval RETURN_SUCCESS            UnitAddress has been fully parsed.
                                    NumResults is set to the number of parsed
                                    values; the corresponding elements have
                                    been set in Result. The rest of Result's
                                    elements are unchanged.

  @retval RETURN_BUFFER_TOO_SMALL   UnitAddress has been fully parsed.
                                    NumResults is set to the number of parsed
                                    values, but elements have been stored only
                                    up to the input value of NumResults, which
                                    is less than what has been parsed.

  @retval RETURN_INVALID_PARAMETER  Parse error. The contents of Results is
                                    indeterminate. NumResults has not been
                                    changed.

**/
STATIC
RETURN_STATUS
ParseUnitAddressHexList (
  IN      SUBSTRING  UnitAddress,
  OUT     UINT32     *Result,
  IN OUT  UINTN      *NumResults
  )
{
  UINTN         Entry;    // number of entry currently being parsed
  UINT32        EntryVal; // value being constructed for current entry
  CHAR8         PrevChr;  // UnitAddress character previously checked
  UINTN         Pos;      // current position within UnitAddress
  RETURN_STATUS Status;

  Entry    = 0;
  EntryVal = 0;
  PrevChr  = ',';

  for (Pos = 0; Pos < UnitAddress.Len; ++Pos) {
    CHAR8 Chr;
    INT8  Val;

    Chr = UnitAddress.Ptr[Pos];
    Val = ('a' <= Chr && Chr <= 'f') ? (Chr - 'a' + 10) :
          ('A' <= Chr && Chr <= 'F') ? (Chr - 'A' + 10) :
          ('0' <= Chr && Chr <= '9') ? (Chr - '0'     ) :
          -1;

    if (Val >= 0) {
      if (EntryVal > 0xFFFFFFF) {
        return RETURN_INVALID_PARAMETER;
      }
      EntryVal = (EntryVal << 4) | Val;
    } else if (Chr == ',') {
      if (PrevChr == ',') {
        return RETURN_INVALID_PARAMETER;
      }
      if (Entry < *NumResults) {
        Result[Entry] = EntryVal;
      }
      ++Entry;
      EntryVal = 0;
    } else {
      return RETURN_INVALID_PARAMETER;
    }

    PrevChr = Chr;
  }

  if (PrevChr == ',') {
    return RETURN_INVALID_PARAMETER;
  }
  if (Entry < *NumResults) {
    Result[Entry] = EntryVal;
    Status = RETURN_SUCCESS;
  } else {
    Status = RETURN_BUFFER_TOO_SMALL;
  }
  ++Entry;

  *NumResults = Entry;
  return Status;
}


/**
  A simple array of Boot Option ID's.
**/
typedef struct {
  UINT16 *Data;
  UINTN  Allocated;
  UINTN  Produced;
} BOOT_ORDER;


/**

  Append BootOptionId to BootOrder, reallocating the latter if needed.

  @param[in out] BootOrder     The structure pointing to the array and holding
                               allocation and usage counters.

  @param[in]     BootOptionId  The value to append to the array.


  @retval RETURN_SUCCESS           BootOptionId appended.

  @retval RETURN_OUT_OF_RESOURCES  Memory reallocation failed.

**/
STATIC
RETURN_STATUS
BootOrderAppend (
  IN OUT  BOOT_ORDER *BootOrder,
  IN      UINT16     BootOptionId
  )
{
  if (BootOrder->Produced == BootOrder->Allocated) {
    UINTN  AllocatedNew;
    UINT16 *DataNew;

    ASSERT (BootOrder->Allocated > 0);
    AllocatedNew = BootOrder->Allocated * 2;
    DataNew = ReallocatePool (
                BootOrder->Allocated * sizeof (*BootOrder->Data),
                AllocatedNew         * sizeof (*DataNew),
                BootOrder->Data
                );
    if (DataNew == NULL) {
      return RETURN_OUT_OF_RESOURCES;
    }
    BootOrder->Allocated = AllocatedNew;
    BootOrder->Data      = DataNew;
  }

  BootOrder->Data[BootOrder->Produced++] = BootOptionId;
  return RETURN_SUCCESS;
}


/**
  OpenFirmware device path node
**/
typedef struct {
  SUBSTRING DriverName;
  SUBSTRING UnitAddress;
  SUBSTRING DeviceArguments;
} OFW_NODE;


/**

  Parse an OpenFirmware device path node into the caller-allocated OFW_NODE
  structure, and advance in the input string.

  The node format is mostly parsed after IEEE 1275-1994, 3.2.1.1 "Node names"
  (a leading slash is expected and not returned):

    /driver-name@unit-address[:device-arguments][<LF>]

  A single trailing <LF> character is consumed but not returned. A trailing
  <LF> or NUL character terminates the device path.

  The function relies on ASCII encoding.

  @param[in out] Ptr      Address of the pointer pointing to the start of the
                          node string. After successful parsing *Ptr is set to
                          the byte immediately following the consumed
                          characters. On error it points to the byte that
                          caused the error. The input string is never modified.

  @param[out]    OfwNode  The members of this structure point into the input
                          string, designating components of the node.
                          Separators are never included. If "device-arguments"
                          is missing, then DeviceArguments.Ptr is set to NULL.
                          All components that are present have nonzero length.

                          If the call doesn't succeed, the contents of this
                          structure is indeterminate.

  @param[out]    IsFinal  In case of successul parsing, this parameter signals
                          whether the node just parsed is the final node in the
                          device path. The call after a final node will attempt
                          to start parsing the next path. If the call doesn't
                          succeed, then this parameter is not changed.


  @retval RETURN_SUCCESS            Parsing successful.

  @retval RETURN_NOT_FOUND          Parsing terminated. *Ptr was (and is)
                                    pointing to an empty string.

  @retval RETURN_INVALID_PARAMETER  Parse error.

**/
STATIC
RETURN_STATUS
ParseOfwNode (
  IN OUT  CONST CHAR8 **Ptr,
  OUT     OFW_NODE    *OfwNode,
  OUT     BOOLEAN     *IsFinal
  )
{
  //
  // A leading slash is expected. End of string is tolerated.
  //
  switch (**Ptr) {
  case '\0':
    return RETURN_NOT_FOUND;

  case '/':
    ++*Ptr;
    break;

  default:
    return RETURN_INVALID_PARAMETER;
  }

  //
  // driver-name
  //
  OfwNode->DriverName.Ptr = *Ptr;
  OfwNode->DriverName.Len = 0;
  while (OfwNode->DriverName.Len < 32 &&
         (IsAlnum (**Ptr) || IsDriverNamePunct (**Ptr))
         ) {
    ++*Ptr;
    ++OfwNode->DriverName.Len;
  }

  if (OfwNode->DriverName.Len == 0 || OfwNode->DriverName.Len == 32) {
    return RETURN_INVALID_PARAMETER;
  }


  //
  // unit-address
  //
  if (**Ptr != '@') {
    return RETURN_INVALID_PARAMETER;
  }
  ++*Ptr;

  OfwNode->UnitAddress.Ptr = *Ptr;
  OfwNode->UnitAddress.Len = 0;
  while (IsPrintNotDelim (**Ptr)) {
    ++*Ptr;
    ++OfwNode->UnitAddress.Len;
  }

  if (OfwNode->UnitAddress.Len == 0) {
    return RETURN_INVALID_PARAMETER;
  }


  //
  // device-arguments, may be omitted
  //
  OfwNode->DeviceArguments.Len = 0;
  if (**Ptr == ':') {
    ++*Ptr;
    OfwNode->DeviceArguments.Ptr = *Ptr;

    while (IsPrintNotDelim (**Ptr)) {
      ++*Ptr;
      ++OfwNode->DeviceArguments.Len;
    }

    if (OfwNode->DeviceArguments.Len == 0) {
      return RETURN_INVALID_PARAMETER;
    }
  }
  else {
    OfwNode->DeviceArguments.Ptr = NULL;
  }

  switch (**Ptr) {
  case '\n':
    ++*Ptr;
    //
    // fall through
    //

  case '\0':
    *IsFinal = TRUE;
    break;

  case '/':
    *IsFinal = FALSE;
    break;

  default:
    return RETURN_INVALID_PARAMETER;
  }

  DEBUG ((
    DEBUG_VERBOSE,
    "%a: DriverName=\"%.*a\" UnitAddress=\"%.*a\" DeviceArguments=\"%.*a\"\n",
    __FUNCTION__,
    OfwNode->DriverName.Len, OfwNode->DriverName.Ptr,
    OfwNode->UnitAddress.Len, OfwNode->UnitAddress.Ptr,
    OfwNode->DeviceArguments.Len,
    OfwNode->DeviceArguments.Ptr == NULL ? "" : OfwNode->DeviceArguments.Ptr
    ));
  return RETURN_SUCCESS;
}


/**

  Translate an array of OpenFirmware device nodes to a UEFI device path
  fragment.

  @param[in]     OfwNode         Array of OpenFirmware device nodes to
                                 translate, constituting the beginning of an
                                 OpenFirmware device path.

  @param[in]     NumNodes        Number of elements in OfwNode.

  @param[out]    Translated      Destination array receiving the UEFI path
                                 fragment, allocated by the caller. If the
                                 return value differs from RETURN_SUCCESS, its
                                 contents is indeterminate.

  @param[in out] TranslatedSize  On input, the number of CHAR16's in
                                 Translated. On RETURN_SUCCESS this parameter
                                 is assigned the number of non-NUL CHAR16's
                                 written to Translated. In case of other return
                                 values, TranslatedSize is indeterminate.


  @retval RETURN_SUCCESS           Translation successful.

  @retval RETURN_BUFFER_TOO_SMALL  The translation does not fit into the number
                                   of bytes provided.

  @retval RETURN_UNSUPPORTED       The array of OpenFirmware device nodes can't
                                   be translated in the current implementation.

**/
STATIC
RETURN_STATUS
TranslateOfwNodes (
  IN      CONST OFW_NODE *OfwNode,
  IN      UINTN          NumNodes,
  OUT     CHAR16         *Translated,
  IN OUT  UINTN          *TranslatedSize
  )
{
  UINT32 PciDevFun[2];
  UINTN  NumEntries;
  UINTN  Written;

  //
  // Get PCI device and optional PCI function. Assume a single PCI root.
  //
  if (NumNodes < FIXED_OFW_NODES ||
      !SubstringEq (OfwNode[0].DriverName, "pci")
      ) {
    return RETURN_UNSUPPORTED;
  }
  PciDevFun[1] = 0;
  NumEntries = sizeof (PciDevFun) / sizeof (PciDevFun[0]);
  if (ParseUnitAddressHexList (
        OfwNode[1].UnitAddress,
        PciDevFun,
        &NumEntries
        ) != RETURN_SUCCESS
      ) {
    return RETURN_UNSUPPORTED;
  }

  if (SubstringEq (OfwNode[1].DriverName, "ide") &&
      SubstringEq (OfwNode[2].DriverName, "drive") &&
      SubstringEq (OfwNode[3].DriverName, "disk")
      ) {
    //
    // OpenFirmware device path (IDE disk, IDE CD-ROM):
    //
    //   /pci@i0cf8/ide@1,1/drive@0/disk@0
    //        ^         ^ ^       ^      ^
    //        |         | |       |      master or slave
    //        |         | |       primary or secondary
    //        |         PCI slot & function holding IDE controller
    //        PCI root at system bus port, PIO
    //
    // UEFI device path:
    //
    //   PciRoot(0x0)/Pci(0x1,0x1)/Ata(Primary,Master,0x0)
    //                                                ^
    //                                                fixed LUN
    //
    UINT32 Secondary;
    UINT32 Slave;

    NumEntries = 1;
    if (ParseUnitAddressHexList (
          OfwNode[2].UnitAddress,
          &Secondary,
          &NumEntries
          ) != RETURN_SUCCESS ||
        Secondary > 1 ||
        ParseUnitAddressHexList (
          OfwNode[3].UnitAddress,
          &Slave,
          &NumEntries // reuse after previous single-element call
          ) != RETURN_SUCCESS ||
        Slave > 1
        ) {
      return RETURN_UNSUPPORTED;
    }

    Written = UnicodeSPrintAsciiFormat (
      Translated,
      *TranslatedSize * sizeof (*Translated), // BufferSize in bytes
      "PciRoot(0x0)/Pci(0x%x,0x%x)/Ata(%a,%a,0x0)",
      PciDevFun[0],
      PciDevFun[1],
      Secondary ? "Secondary" : "Primary",
      Slave ? "Slave" : "Master"
      );
  } else if (SubstringEq (OfwNode[1].DriverName, "isa") &&
             SubstringEq (OfwNode[2].DriverName, "fdc") &&
             SubstringEq (OfwNode[3].DriverName, "floppy")
             ) {
    //
    // OpenFirmware device path (floppy disk):
    //
    //   /pci@i0cf8/isa@1/fdc@03f0/floppy@0
    //        ^         ^     ^           ^
    //        |         |     |           A: or B:
    //        |         |     ISA controller io-port (hex)
    //        |         PCI slot holding ISA controller
    //        PCI root at system bus port, PIO
    //
    // UEFI device path:
    //
    //   PciRoot(0x0)/Pci(0x1,0x0)/Floppy(0x0)
    //                                    ^
    //                                    ACPI UID
    //
    UINT32 AcpiUid;

    NumEntries = 1;
    if (ParseUnitAddressHexList (
          OfwNode[3].UnitAddress,
          &AcpiUid,
          &NumEntries
          ) != RETURN_SUCCESS ||
        AcpiUid > 1
        ) {
      return RETURN_UNSUPPORTED;
    }

    Written = UnicodeSPrintAsciiFormat (
      Translated,
      *TranslatedSize * sizeof (*Translated), // BufferSize in bytes
      "PciRoot(0x0)/Pci(0x%x,0x%x)/Floppy(0x%x)",
      PciDevFun[0],
      PciDevFun[1],
      AcpiUid
      );
   } else {
     return RETURN_UNSUPPORTED;
   }

  //
  // There's no way to differentiate between "completely used up without
  // truncation" and "truncated", so treat the former as the latter, and return
  // success only for "some room left unused".
  //
  if (Written + 1 < *TranslatedSize) {
    *TranslatedSize = Written;
    return RETURN_SUCCESS;
  }

  return RETURN_BUFFER_TOO_SMALL;
}


/**

  Translate an OpenFirmware device path fragment to a UEFI device path
  fragment, and advance in the input string.

  @param[in out] Ptr             Address of the pointer pointing to the start
                                 of the path string. After successful
                                 translation (RETURN_SUCCESS) or at least
                                 successful parsing (RETURN_UNSUPPORTED,
                                 RETURN_BUFFER_TOO_SMALL), *Ptr is set to the
                                 byte immediately following the consumed
                                 characters. In other error cases, it points to
                                 the byte that caused the error.

  @param[out]    Translated      Destination array receiving the UEFI path
                                 fragment, allocated by the caller. If the
                                 return value differs from RETURN_SUCCESS, its
                                 contents is indeterminate.

  @param[in out] TranslatedSize  On input, the number of CHAR16's in
                                 Translated. On RETURN_SUCCESS this parameter
                                 is assigned the number of non-NUL CHAR16's
                                 written to Translated. In case of other return
                                 values, TranslatedSize is indeterminate.


  @retval RETURN_SUCCESS            Translation successful.

  @retval RETURN_BUFFER_TOO_SMALL   The OpenFirmware device path was parsed
                                    successfully, but its translation did not
                                    fit into the number of bytes provided.
                                    Further calls to this function are
                                    possible.

  @retval RETURN_UNSUPPORTED        The OpenFirmware device path was parsed
                                    successfully, but it can't be translated in
                                    the current implementation. Further calls
                                    to this function are possible.

  @retval RETURN_NOT_FOUND          Translation terminated, *Ptr was (and is)
                                    pointing to an empty string.

  @retval RETURN_INVALID_PARAMETER  Parse error. This is a permanent error.

**/
STATIC
RETURN_STATUS
TranslateOfwPath (
  IN OUT  CONST CHAR8 **Ptr,
  OUT     CHAR16      *Translated,
  IN OUT  UINTN       *TranslatedSize
  )
{
  UINTN         NumNodes;
  RETURN_STATUS Status;
  OFW_NODE      Node[FIXED_OFW_NODES];
  BOOLEAN       IsFinal;
  OFW_NODE      Skip;

  NumNodes = 0;
  Status = ParseOfwNode (Ptr, &Node[NumNodes], &IsFinal);

  if (Status == RETURN_NOT_FOUND) {
    DEBUG ((DEBUG_VERBOSE, "%a: no more nodes\n", __FUNCTION__));
    return RETURN_NOT_FOUND;
  }

  while (Status == RETURN_SUCCESS && !IsFinal) {
    ++NumNodes;
    Status = ParseOfwNode (
               Ptr,
               (NumNodes < FIXED_OFW_NODES) ? &Node[NumNodes] : &Skip,
               &IsFinal
               );
  }

  switch (Status) {
  case RETURN_SUCCESS:
    ++NumNodes;
    break;

  case RETURN_INVALID_PARAMETER:
    DEBUG ((DEBUG_VERBOSE, "%a: parse error\n", __FUNCTION__));
    return RETURN_INVALID_PARAMETER;

  default:
    ASSERT (0);
  }

  Status = TranslateOfwNodes (
             Node,
             NumNodes < FIXED_OFW_NODES ? NumNodes : FIXED_OFW_NODES,
             Translated,
             TranslatedSize);
  switch (Status) {
  case RETURN_SUCCESS:
    DEBUG ((DEBUG_VERBOSE, "%a: success: \"%s\"\n", __FUNCTION__, Translated));
    break;

  case RETURN_BUFFER_TOO_SMALL:
    DEBUG ((DEBUG_VERBOSE, "%a: buffer too small\n", __FUNCTION__));
    break;

  case RETURN_UNSUPPORTED:
    DEBUG ((DEBUG_VERBOSE, "%a: unsupported\n", __FUNCTION__));
    break;

  default:
    ASSERT (0);
  }
  return Status;
}


/**

  Convert the UEFI DevicePath to full text representation with DevPathToText,
  then match the UEFI device path fragment in Translated against it.

  @param[in] Translated        UEFI device path fragment, translated from
                               OpenFirmware format, to search for.

  @param[in] TranslatedLength  The length of Translated in CHAR16's.

  @param[in] DevicePath        Boot option device path whose textual rendering
                               to search in.

  @param[in] DevPathToText  Binary-to-text conversion protocol for DevicePath.


  @retval TRUE   If Translated was found at the beginning of DevicePath after
                 converting the latter to text.

  @retval FALSE  If DevicePath was NULL, or it could not be converted, or there
                 was no match.

**/
STATIC
BOOLEAN
Match (
  IN  CONST CHAR16                           *Translated,
  IN  UINTN                                  TranslatedLength,
  IN  CONST EFI_DEVICE_PATH_PROTOCOL         *DevicePath,
  IN  CONST EFI_DEVICE_PATH_TO_TEXT_PROTOCOL *DevPathToText
  )
{
  CHAR16  *Converted;
  BOOLEAN Result;

  Converted = DevPathToText->ConvertDevicePathToText (
                               DevicePath,
                               FALSE, // DisplayOnly
                               FALSE  // AllowShortcuts
                               );
  if (Converted == NULL) {
    return FALSE;
  }

  //
  // Is Translated a prefix of Converted?
  //
  Result = (StrnCmp (Converted, Translated, TranslatedLength) == 0);
  DEBUG ((
    DEBUG_VERBOSE,
    "%a: against \"%s\": %a\n",
    __FUNCTION__,
    Converted,
    Result ? "match" : "no match"
    ));
  FreePool (Converted);
  return Result;
}


/**

  Set the boot order based on configuration retrieved from QEMU.

  Attempt to retrieve the "bootorder" fw_cfg file from QEMU. Translate the
  OpenFirmware device paths therein to UEFI device path fragments. Match the
  translated fragments against BootOptionList, and rewrite the BootOrder NvVar
  so that it corresponds to the order described in fw_cfg.

  @param[in] BootOptionList  A boot option list, created with
                             BdsLibEnumerateAllBootOption ().


  @retval RETURN_SUCCESS            BootOrder NvVar rewritten.

  @retval RETURN_UNSUPPORTED        QEMU's fw_cfg is not supported.

  @retval RETURN_NOT_FOUND          Empty or nonexistent "bootorder" fw_cfg
                                    file, or no match found between the
                                    "bootorder" fw_cfg file and BootOptionList.

  @retval RETURN_INVALID_PARAMETER  Parse error in the "bootorder" fw_cfg file.

  @retval RETURN_OUT_OF_RESOURCES   Memory allocation failed.

  @return                           Values returned by gBS->LocateProtocol ()
                                    or gRT->SetVariable ().

**/
RETURN_STATUS
SetBootOrderFromQemu (
  IN  CONST LIST_ENTRY *BootOptionList
  )
{
  RETURN_STATUS                    Status;

  EFI_DEVICE_PATH_TO_TEXT_PROTOCOL *DevPathToText;

  FIRMWARE_CONFIG_ITEM             FwCfgItem;
  UINTN                            FwCfgSize;
  CHAR8                            *FwCfg;
  CONST CHAR8                      *FwCfgPtr;

  BOOT_ORDER                       BootOrder;

  UINTN                            TranslatedSize;
  CHAR16                           Translated[TRANSLATION_OUTPUT_SIZE];

  Status = gBS->LocateProtocol (
                  &gEfiDevicePathToTextProtocolGuid,
                  NULL, // optional registration key
                  (VOID **) &DevPathToText
                  );
  if (Status != EFI_SUCCESS) {
    return Status;
  }

  Status = QemuFwCfgFindFile ("bootorder", &FwCfgItem, &FwCfgSize);
  if (Status != RETURN_SUCCESS) {
    return Status;
  }

  if (FwCfgSize == 0) {
    return RETURN_NOT_FOUND;
  }

  FwCfg = AllocatePool (FwCfgSize);
  if (FwCfg == NULL) {
    return RETURN_OUT_OF_RESOURCES;
  }

  QemuFwCfgSelectItem (FwCfgItem);
  QemuFwCfgReadBytes (FwCfgSize, FwCfg);
  if (FwCfg[FwCfgSize - 1] != '\0') {
    Status = RETURN_INVALID_PARAMETER;
    goto ErrorFreeFwCfg;
  }

  DEBUG ((DEBUG_VERBOSE, "%a: FwCfg:\n", __FUNCTION__));
  DEBUG ((DEBUG_VERBOSE, "%a\n", FwCfg));
  DEBUG ((DEBUG_VERBOSE, "%a: FwCfg: <end>\n", __FUNCTION__));
  FwCfgPtr = FwCfg;

  BootOrder.Produced  = 0;
  BootOrder.Allocated = 1;
  BootOrder.Data = AllocatePool (
                     BootOrder.Allocated * sizeof (*BootOrder.Data)
                     );
  if (BootOrder.Data == NULL) {
    Status = RETURN_OUT_OF_RESOURCES;
    goto ErrorFreeFwCfg;
  }

  //
  // translate each OpenFirmware path
  //
  TranslatedSize = sizeof (Translated) / sizeof (Translated[0]);
  Status = TranslateOfwPath (&FwCfgPtr, Translated, &TranslatedSize);
  while (Status == RETURN_SUCCESS ||
         Status == RETURN_UNSUPPORTED ||
         Status == RETURN_BUFFER_TOO_SMALL) {
    if (Status == RETURN_SUCCESS) {
      CONST LIST_ENTRY *Link;

      //
      // match translated OpenFirmware path against all enumerated boot options
      //
      for (Link = BootOptionList->ForwardLink; Link != BootOptionList;
           Link = Link->ForwardLink) {
        CONST BDS_COMMON_OPTION *BootOption;

        BootOption = CR (
                       Link,
                       BDS_COMMON_OPTION,
                       Link,
                       BDS_LOAD_OPTION_SIGNATURE
                       );
        if (IS_LOAD_OPTION_TYPE (BootOption->Attribute, LOAD_OPTION_ACTIVE) &&
            Match (
              Translated,
              TranslatedSize, // contains length, not size, in CHAR16's here
              BootOption->DevicePath,
              DevPathToText
              )
            ) {
          //
          // match found, store ID and continue with next OpenFirmware path
          //
          Status = BootOrderAppend (&BootOrder, BootOption->BootCurrent);
          if (Status != RETURN_SUCCESS) {
            goto ErrorFreeBootOrder;
          }
          break;
        }
      } // scanned all enumerated boot options
    }   // translation successful

    TranslatedSize = sizeof (Translated) / sizeof (Translated[0]);
    Status = TranslateOfwPath (&FwCfgPtr, Translated, &TranslatedSize);
  } // scanning of OpenFirmware paths done

  if (Status == RETURN_NOT_FOUND && BootOrder.Produced > 0) {
    //
    // No more OpenFirmware paths, some matches found: rewrite BootOrder NvVar.
    // See Table 10 in the UEFI Spec 2.3.1 with Errata C for the required
    // attributes.
    //
    Status = gRT->SetVariable (
                    L"BootOrder",
                    &gEfiGlobalVariableGuid,
                    EFI_VARIABLE_NON_VOLATILE |
                      EFI_VARIABLE_BOOTSERVICE_ACCESS |
                      EFI_VARIABLE_RUNTIME_ACCESS,
                    BootOrder.Produced * sizeof (*BootOrder.Data),
                    BootOrder.Data
                    );
    DEBUG ((
      DEBUG_INFO,
      "%a: setting BootOrder: %a\n",
      __FUNCTION__,
      Status == EFI_SUCCESS ? "success" : "error"
      ));
  }

ErrorFreeBootOrder:
  FreePool (BootOrder.Data);

ErrorFreeFwCfg:
  FreePool (FwCfg);

  return Status;
}