xref: /device/linaro/bootloader/edk2/ArmPkg/Filesystem/SemihostFs/Arm/SemihostFs.c

/** @file
  Support a Semi Host file system over a debuggers JTAG

  Copyright (c) 2008 - 2009, Apple Inc. All rights reserved.<BR>
  Portions copyright (c) 2011 - 2014, ARM Ltd. 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 <Uefi.h>

#include <Guid/FileInfo.h>
#include <Guid/FileSystemInfo.h>
#include <Guid/FileSystemVolumeLabelInfo.h>

#include <Library/BaseLib.h>
#include <Library/BaseMemoryLib.h>
#include <Library/DebugLib.h>
#include <Library/MemoryAllocationLib.h>
#include <Library/SemihostLib.h>
#include <Library/UefiBootServicesTableLib.h>
#include <Library/UefiLib.h>

#include <Protocol/DevicePath.h>
#include <Protocol/SimpleFileSystem.h>

#include "SemihostFs.h"

#define DEFAULT_SEMIHOST_FS_LABEL   L"SemihostFs"

STATIC CHAR16 *mSemihostFsLabel;

EFI_SIMPLE_FILE_SYSTEM_PROTOCOL gSemihostFs = {
  EFI_SIMPLE_FILE_SYSTEM_PROTOCOL_REVISION,
  VolumeOpen
};

EFI_FILE gSemihostFsFile = {
  EFI_FILE_PROTOCOL_REVISION,
  FileOpen,
  FileClose,
  FileDelete,
  FileRead,
  FileWrite,
  FileGetPosition,
  FileSetPosition,
  FileGetInfo,
  FileSetInfo,
  FileFlush
};

//
// Device path for semi-hosting. It contains our autogened Caller ID GUID.
//
typedef struct {
  VENDOR_DEVICE_PATH        Guid;
  EFI_DEVICE_PATH_PROTOCOL  End;
} SEMIHOST_DEVICE_PATH;

SEMIHOST_DEVICE_PATH gDevicePath = {
  {
    { HARDWARE_DEVICE_PATH, HW_VENDOR_DP, { sizeof (VENDOR_DEVICE_PATH), 0 } },
    EFI_CALLER_ID_GUID
  },
  { END_DEVICE_PATH_TYPE, END_ENTIRE_DEVICE_PATH_SUBTYPE, { sizeof (EFI_DEVICE_PATH_PROTOCOL), 0 } }
};

typedef struct {
  LIST_ENTRY    Link;
  UINT64        Signature;
  EFI_FILE      File;
  CHAR8         *FileName;
  UINT64        OpenMode;
  UINT32        Position;
  UINTN         SemihostHandle;
  BOOLEAN       IsRoot;
  EFI_FILE_INFO Info;
} SEMIHOST_FCB;

#define SEMIHOST_FCB_SIGNATURE      SIGNATURE_32( 'S', 'H', 'F', 'C' )
#define SEMIHOST_FCB_FROM_THIS(a)   CR(a, SEMIHOST_FCB, File, SEMIHOST_FCB_SIGNATURE)
#define SEMIHOST_FCB_FROM_LINK(a)   CR(a, SEMIHOST_FCB, Link, SEMIHOST_FCB_SIGNATURE);

EFI_HANDLE  gInstallHandle = NULL;
LIST_ENTRY  gFileList = INITIALIZE_LIST_HEAD_VARIABLE (gFileList);

SEMIHOST_FCB *
AllocateFCB (
  VOID
  )
{
  SEMIHOST_FCB *Fcb = AllocateZeroPool (sizeof (SEMIHOST_FCB));

  if (Fcb != NULL) {
    CopyMem (&Fcb->File, &gSemihostFsFile, sizeof (gSemihostFsFile));
    Fcb->Signature = SEMIHOST_FCB_SIGNATURE;
  }

  return Fcb;
}

VOID
FreeFCB (
  IN SEMIHOST_FCB *Fcb
  )
{
  // Remove Fcb from gFileList.
  RemoveEntryList (&Fcb->Link);

  // To help debugging...
  Fcb->Signature = 0;

  FreePool (Fcb);
}



EFI_STATUS
VolumeOpen (
  IN  EFI_SIMPLE_FILE_SYSTEM_PROTOCOL *This,
  OUT EFI_FILE                        **Root
  )
{
  SEMIHOST_FCB *RootFcb = NULL;

  if (Root == NULL) {
    return EFI_INVALID_PARAMETER;
  }

  RootFcb = AllocateFCB ();
  if (RootFcb == NULL) {
    return EFI_OUT_OF_RESOURCES;
  }

  RootFcb->IsRoot = TRUE;
  RootFcb->Info.Attribute = EFI_FILE_READ_ONLY | EFI_FILE_DIRECTORY;

  InsertTailList (&gFileList, &RootFcb->Link);

  *Root = &RootFcb->File;

  return EFI_SUCCESS;
}

/**
  Open a file on the host system by means of the semihosting interface.

  @param[in]   This        A pointer to the EFI_FILE_PROTOCOL instance that is
                           the file handle to source location.
  @param[out]  NewHandle   A pointer to the location to return the opened
                           handle for the new file.
  @param[in]   FileName    The Null-terminated string of the name of the file
                           to be opened.
  @param[in]   OpenMode    The mode to open the file : Read or Read/Write or
                           Read/Write/Create
  @param[in]   Attributes  Only valid for EFI_FILE_MODE_CREATE, in which case these
                           are the attribute bits for the newly created file. The
                           mnemonics of the attribute bits are : EFI_FILE_READ_ONLY,
                           EFI_FILE_HIDDEN, EFI_FILE_SYSTEM, EFI_FILE_RESERVED,
                           EFI_FILE_DIRECTORY and EFI_FILE_ARCHIVE.

  @retval  EFI_SUCCESS            The file was open.
  @retval  EFI_NOT_FOUND          The specified file could not be found.
  @retval  EFI_DEVICE_ERROR       The last issued semi-hosting operation failed.
  @retval  EFI_WRITE_PROTECTED    Attempt to create a directory. This is not possible
                                  with the semi-hosting interface.
  @retval  EFI_OUT_OF_RESOURCES   Not enough resources were available to open the file.
  @retval  EFI_INVALID_PARAMETER  At least one of the parameters is invalid.

**/
EFI_STATUS
FileOpen (
  IN  EFI_FILE  *This,
  OUT EFI_FILE  **NewHandle,
  IN  CHAR16    *FileName,
  IN  UINT64    OpenMode,
  IN  UINT64    Attributes
  )
{
  SEMIHOST_FCB   *FileFcb;
  RETURN_STATUS  Return;
  EFI_STATUS     Status;
  UINTN          SemihostHandle;
  CHAR8          *AsciiFileName;
  UINT32         SemihostMode;
  UINTN          Length;

  if ((FileName == NULL) || (NewHandle == NULL)) {
    return EFI_INVALID_PARAMETER;
  }

  if ( (OpenMode != EFI_FILE_MODE_READ) &&
       (OpenMode != (EFI_FILE_MODE_READ | EFI_FILE_MODE_WRITE)) &&
       (OpenMode != (EFI_FILE_MODE_READ | EFI_FILE_MODE_WRITE | EFI_FILE_MODE_CREATE)) ) {
    return EFI_INVALID_PARAMETER;
  }

  if ((OpenMode & EFI_FILE_MODE_CREATE) &&
      (Attributes & EFI_FILE_DIRECTORY)    ) {
    return EFI_WRITE_PROTECTED;
  }

  Length = StrLen (FileName) + 1;
  AsciiFileName = AllocatePool (Length);
  if (AsciiFileName == NULL) {
    return EFI_OUT_OF_RESOURCES;
  }
  UnicodeStrToAsciiStrS (FileName, AsciiFileName, Length);

  // Opening '/', '\', '.', or the NULL pathname is trying to open the root directory
  if ((AsciiStrCmp (AsciiFileName, "\\") == 0) ||
      (AsciiStrCmp (AsciiFileName, "/")  == 0) ||
      (AsciiStrCmp (AsciiFileName, "")   == 0) ||
      (AsciiStrCmp (AsciiFileName, ".")  == 0)    ) {
    FreePool (AsciiFileName);
    return (VolumeOpen (&gSemihostFs, NewHandle));
  }

  //
  // No control is done here concerning the file path. It is passed
  // as it is to the host operating system through the semi-hosting
  // interface. We first try to open the file in the read or update
  // mode even if the file creation has been asked for. That way, if
  // the file already exists, it is not truncated to zero length. In
  // write mode (bit SEMIHOST_FILE_MODE_WRITE up), if the file already
  // exists, it is reset to an empty file.
  //
  if (OpenMode == EFI_FILE_MODE_READ) {
    SemihostMode = SEMIHOST_FILE_MODE_READ | SEMIHOST_FILE_MODE_BINARY;
  } else {
    SemihostMode = SEMIHOST_FILE_MODE_READ | SEMIHOST_FILE_MODE_BINARY | SEMIHOST_FILE_MODE_UPDATE;
  }
  Return = SemihostFileOpen (AsciiFileName, SemihostMode, &SemihostHandle);

  if (RETURN_ERROR (Return)) {
    if (OpenMode & EFI_FILE_MODE_CREATE) {
      //
      // In the create if does not exist case, if the opening in update
      // mode failed, create it and open it in update mode. The update
      // mode allows for both read and write from and to the file.
      //
      Return = SemihostFileOpen (
                 AsciiFileName,
                 SEMIHOST_FILE_MODE_WRITE | SEMIHOST_FILE_MODE_BINARY | SEMIHOST_FILE_MODE_UPDATE,
                 &SemihostHandle
                 );
      if (RETURN_ERROR (Return)) {
        Status = EFI_DEVICE_ERROR;
        goto Error;
      }
    } else {
      Status = EFI_NOT_FOUND;
      goto Error;
    }
  }

  // Allocate a control block and fill it
  FileFcb = AllocateFCB ();
  if (FileFcb == NULL) {
    Status = EFI_OUT_OF_RESOURCES;
    goto Error;
  }

  FileFcb->FileName       = AsciiFileName;
  FileFcb->SemihostHandle = SemihostHandle;
  FileFcb->Position       = 0;
  FileFcb->IsRoot         = 0;
  FileFcb->OpenMode       = OpenMode;

  Return = SemihostFileLength (SemihostHandle, &Length);
  if (RETURN_ERROR (Return)) {
    Status = EFI_DEVICE_ERROR;
    FreeFCB (FileFcb);
    goto Error;
  }

  FileFcb->Info.FileSize     = Length;
  FileFcb->Info.PhysicalSize = Length;
  FileFcb->Info.Attribute    = (OpenMode & EFI_FILE_MODE_CREATE) ? Attributes : 0;

  InsertTailList (&gFileList, &FileFcb->Link);

  *NewHandle = &FileFcb->File;

  return EFI_SUCCESS;

Error:

  FreePool (AsciiFileName);

  return Status;
}

/**
  Worker function that truncate a file specified by its name to a given size.

  @param[in]  FileName  The Null-terminated string of the name of the file to be opened.
  @param[in]  Size      The target size for the file.

  @retval  EFI_SUCCESS       The file was truncated.
  @retval  EFI_DEVICE_ERROR  The last issued semi-hosting operation failed.

**/
STATIC
EFI_STATUS
TruncateFile (
  IN CHAR8  *FileName,
  IN UINTN   Size
  )
{
  EFI_STATUS     Status;
  RETURN_STATUS  Return;
  UINTN          FileHandle;
  UINT8          *Buffer;
  UINTN          Remaining;
  UINTN          Read;
  UINTN          ToRead;

  Status     = EFI_DEVICE_ERROR;
  FileHandle = 0;
  Buffer     = NULL;

  Return = SemihostFileOpen (
             FileName,
             SEMIHOST_FILE_MODE_READ | SEMIHOST_FILE_MODE_BINARY,
             &FileHandle
             );
  if (RETURN_ERROR (Return)) {
    goto Error;
  }

  Buffer = AllocatePool (Size);
  if (Buffer == NULL) {
    Status = EFI_OUT_OF_RESOURCES;
    goto Error;
  }

  Read = 0;
  Remaining = Size;
  while (Remaining > 0) {
    ToRead = Remaining;
    Return = SemihostFileRead (FileHandle, &ToRead, Buffer + Read);
    if (RETURN_ERROR (Return)) {
      goto Error;
    }
    Remaining -= ToRead;
    Read      += ToRead;
  }

  Return = SemihostFileClose (FileHandle);
  FileHandle = 0;
  if (RETURN_ERROR (Return)) {
    goto Error;
  }

  Return = SemihostFileOpen (
             FileName,
             SEMIHOST_FILE_MODE_WRITE | SEMIHOST_FILE_MODE_BINARY,
             &FileHandle
             );
  if (RETURN_ERROR (Return)) {
    goto Error;
  }

  if (Size > 0) {
    Return = SemihostFileWrite (FileHandle, &Size, Buffer);
    if (RETURN_ERROR (Return)) {
      goto Error;
    }
  }

  Status = EFI_SUCCESS;

Error:

  if (FileHandle != 0) {
    SemihostFileClose (FileHandle);
  }
  if (Buffer != NULL) {
    FreePool (Buffer);
  }

  return (Status);

}

/**
  Close a specified file handle.

  @param[in]  This  A pointer to the EFI_FILE_PROTOCOL instance that is the file
                    handle to close.

  @retval  EFI_SUCCESS            The file was closed.
  @retval  EFI_INVALID_PARAMETER  The parameter "This" is NULL.

**/
EFI_STATUS
FileClose (
  IN EFI_FILE  *This
  )
{
  SEMIHOST_FCB   *Fcb;

  if (This == NULL) {
    return EFI_INVALID_PARAMETER;
  }

  Fcb = SEMIHOST_FCB_FROM_THIS(This);

  if (!Fcb->IsRoot) {
    SemihostFileClose (Fcb->SemihostHandle);
    //
    // The file size might have been reduced from its actual
    // size on the host file system with FileSetInfo(). In
    // that case, the file has to be truncated.
    //
    if (Fcb->Info.FileSize < Fcb->Info.PhysicalSize) {
      TruncateFile (Fcb->FileName, Fcb->Info.FileSize);
    }
    FreePool (Fcb->FileName);
  }

  FreeFCB (Fcb);

  return EFI_SUCCESS;
}

/**
  Close and delete a file.

  @param[in]  This  A pointer to the EFI_FILE_PROTOCOL instance that is the file
                    handle to delete.

  @retval  EFI_SUCCESS              The file was closed and deleted.
  @retval  EFI_WARN_DELETE_FAILURE  The handle was closed, but the file was not deleted.
  @retval  EFI_INVALID_PARAMETER    The parameter "This" is NULL.

**/
EFI_STATUS
FileDelete (
  IN EFI_FILE *This
  )
{
  SEMIHOST_FCB   *Fcb;
  RETURN_STATUS  Return;
  CHAR8          *FileName;
  UINTN          NameSize;

  if (This == NULL) {
    return EFI_INVALID_PARAMETER;
  }

  Fcb = SEMIHOST_FCB_FROM_THIS (This);

  if (!Fcb->IsRoot) {
    // Get the filename from the Fcb
    NameSize = AsciiStrLen (Fcb->FileName);
    FileName = AllocatePool (NameSize + 1);

    AsciiStrCpyS (FileName, NameSize + 1, Fcb->FileName);

    // Close the file if it's open.  Disregard return status,
    // since it might give an error if the file isn't open.
    This->Close (This);

    // Call the semihost interface to delete the file.
    Return = SemihostFileRemove (FileName);
    if (RETURN_ERROR (Return)) {
      return EFI_WARN_DELETE_FAILURE;
    }
    return EFI_SUCCESS;
  } else {
    return EFI_WARN_DELETE_FAILURE;
  }
}

/**
  Read data from an open file.

  @param[in]      This        A pointer to the EFI_FILE_PROTOCOL instance that
                              is the file handle to read data from.
  @param[in out]  BufferSize  On input, the size of the Buffer. On output, the
                              amount of data returned in Buffer. In both cases,
                              the size is measured in bytes.
  @param[out]     Buffer      The buffer into which the data is read.

  @retval  EFI_SUCCESS            The data was read.
  @retval  EFI_DEVICE_ERROR       On entry, the current file position is
                                  beyond the end of the file, or the semi-hosting
                                  interface reported an error while performing the
                                  read operation.
  @retval  EFI_INVALID_PARAMETER  At least one of the three input pointers is NULL.

**/
EFI_STATUS
FileRead (
  IN     EFI_FILE  *This,
  IN OUT UINTN     *BufferSize,
  OUT    VOID      *Buffer
  )
{
  SEMIHOST_FCB   *Fcb;
  EFI_STATUS     Status;
  RETURN_STATUS  Return;

  if ((This == NULL) || (BufferSize == NULL) || (Buffer == NULL)) {
    return EFI_INVALID_PARAMETER;
  }

  Fcb = SEMIHOST_FCB_FROM_THIS (This);

  if (Fcb->IsRoot) {
    // The semi-hosting interface does not allow to list files on the host machine.
    Status = EFI_UNSUPPORTED;
  } else {
    Status = EFI_SUCCESS;
    if (Fcb->Position >= Fcb->Info.FileSize) {
      *BufferSize = 0;
      if (Fcb->Position > Fcb->Info.FileSize) {
        Status = EFI_DEVICE_ERROR;
      }
    } else {
      Return = SemihostFileRead (Fcb->SemihostHandle, BufferSize, Buffer);
      if (RETURN_ERROR (Return)) {
        Status = EFI_DEVICE_ERROR;
      } else {
        Fcb->Position += *BufferSize;
      }
    }
  }

  return Status;
}

/**
  Worker function that extends the size of an open file.

  The extension is filled with zeros.

  @param[in]  Fcb   Internal description of the opened file
  @param[in]  Size  The number of bytes, the file has to be extended.

  @retval  EFI_SUCCESS       The file was extended.
  @retval  EFI_DEVICE_ERROR  The last issued semi-hosting operation failed.

**/
STATIC
EFI_STATUS
ExtendFile (
  IN  SEMIHOST_FCB  *Fcb,
  IN  UINTN         Size
  )
{
  RETURN_STATUS  Return;
  UINTN          Remaining;
  CHAR8          WriteBuffer[128];
  UINTN          WriteNb;
  UINTN          WriteSize;

  Return = SemihostFileSeek (Fcb->SemihostHandle, Fcb->Info.FileSize);
  if (RETURN_ERROR (Return)) {
    return EFI_DEVICE_ERROR;
  }

  Remaining = Size;
  SetMem (WriteBuffer, 0, sizeof(WriteBuffer));
  while (Remaining > 0) {
    WriteNb = MIN (Remaining, sizeof(WriteBuffer));
    WriteSize = WriteNb;
    Return = SemihostFileWrite (Fcb->SemihostHandle, &WriteSize, WriteBuffer);
    if (RETURN_ERROR (Return)) {
      return EFI_DEVICE_ERROR;
    }
    Remaining -= WriteNb;
  }

  return EFI_SUCCESS;
}

/**
  Write data to an open file.

  @param[in]      This        A pointer to the EFI_FILE_PROTOCOL instance that
                              is the file handle to write data to.
  @param[in out]  BufferSize  On input, the size of the Buffer. On output, the
                              size of the data actually written. In both cases,
                              the size is measured in bytes.
  @param[in]      Buffer      The buffer of data to write.

  @retval  EFI_SUCCESS            The data was written.
  @retval  EFI_ACCESS_DENIED      Attempt to write into a read only file or
                                  in a file opened in read only mode.
  @retval  EFI_DEVICE_ERROR       The last issued semi-hosting operation failed.
  @retval  EFI_INVALID_PARAMETER  At least one of the three input pointers is NULL.

**/
EFI_STATUS
FileWrite (
  IN     EFI_FILE *This,
  IN OUT UINTN    *BufferSize,
  IN     VOID     *Buffer
  )
{
  SEMIHOST_FCB   *Fcb;
  EFI_STATUS     Status;
  UINTN          WriteSize;
  RETURN_STATUS  Return;
  UINTN          Length;

  if ((This == NULL) || (BufferSize == NULL) || (Buffer == NULL)) {
    return EFI_INVALID_PARAMETER;
  }

  Fcb = SEMIHOST_FCB_FROM_THIS (This);

  // We cannot write a read-only file
  if ((Fcb->Info.Attribute & EFI_FILE_READ_ONLY)
      || !(Fcb->OpenMode & EFI_FILE_MODE_WRITE)) {
    return EFI_ACCESS_DENIED;
  }

  //
  // If the position has been set past the end of the file, first grow the
  // file from its current size "Fcb->Info.FileSize" to "Fcb->Position"
  // size, filling the gap with zeros.
  //
  if (Fcb->Position > Fcb->Info.FileSize) {
    Status = ExtendFile (Fcb, Fcb->Position - Fcb->Info.FileSize);
    if (EFI_ERROR (Status)) {
      return Status;
    }
    Fcb->Info.FileSize = Fcb->Position;
  }

  WriteSize = *BufferSize;
  Return = SemihostFileWrite (Fcb->SemihostHandle, &WriteSize, Buffer);
  if (RETURN_ERROR (Return)) {
    return EFI_DEVICE_ERROR;
  }

  Fcb->Position += *BufferSize;
  if (Fcb->Position > Fcb->Info.FileSize) {
    Fcb->Info.FileSize = Fcb->Position;
  }

  Return = SemihostFileLength (Fcb->SemihostHandle, &Length);
  if (RETURN_ERROR (Return)) {
    return EFI_DEVICE_ERROR;
  }
  Fcb->Info.PhysicalSize = Length;

  return EFI_SUCCESS;
}

/**
  Return a file's current position.

  @param[in]   This      A pointer to the EFI_FILE_PROTOCOL instance that is
                         the file handle to get the current position on.
  @param[out]  Position  The address to return the file's current position value.

  @retval  EFI_SUCCESS            The position was returned.
  @retval  EFI_INVALID_PARAMETER  The parameter "This" or "Position" is NULL.

**/
EFI_STATUS
FileGetPosition (
  IN  EFI_FILE    *This,
  OUT UINT64      *Position
  )
{
  SEMIHOST_FCB *Fcb;

  if ((This == NULL) || (Position == NULL)) {
    return EFI_INVALID_PARAMETER;
  }

  Fcb = SEMIHOST_FCB_FROM_THIS(This);

  *Position = Fcb->Position;

  return EFI_SUCCESS;
}

/**
  Set a file's current position.

  @param[in]  This      A pointer to the EFI_FILE_PROTOCOL instance that is
                        the file handle to set the requested position on.
  @param[in]  Position  The byte position from the start of the file to set.

  @retval  EFI_SUCCESS       The position was set.
  @retval  EFI_DEVICE_ERROR  The semi-hosting positionning operation failed.
  @retval  EFI_UNSUPPORTED   The seek request for nonzero is not valid on open
                             directories.
  @retval  EFI_INVALID_PARAMETER  The parameter "This" is NULL.

**/
EFI_STATUS
FileSetPosition (
  IN EFI_FILE *This,
  IN UINT64   Position
  )
{
  SEMIHOST_FCB   *Fcb;
  RETURN_STATUS  Return;

  if (This == NULL) {
    return EFI_INVALID_PARAMETER;
  }

  Fcb = SEMIHOST_FCB_FROM_THIS (This);

  if (Fcb->IsRoot) {
    if (Position != 0) {
      return EFI_UNSUPPORTED;
    }
  }
  else {
    //
    // UEFI Spec section 12.5:
    // "Seeking to position 0xFFFFFFFFFFFFFFFF causes the current position to
    // be set to the end of the file."
    //
    if (Position == 0xFFFFFFFFFFFFFFFF) {
      Position = Fcb->Info.FileSize;
    }
    Return = SemihostFileSeek (Fcb->SemihostHandle, MIN (Position, Fcb->Info.FileSize));
    if (RETURN_ERROR (Return)) {
      return EFI_DEVICE_ERROR;
    }
  }

  Fcb->Position = Position;

  return EFI_SUCCESS;
}

/**
  Return information about a file.

  @param[in]      Fcb         A pointer to the description of an open file.
  @param[in out]  BufferSize  The size, in bytes, of Buffer.
  @param[out]     Buffer      A pointer to the data buffer to return. Not NULL if
                              "*BufferSize" is greater than 0.

  @retval  EFI_SUCCESS            The information was returned.
  @retval  EFI_BUFFER_TOO_SMALL   The BufferSize is too small to return the information.
                                  BufferSize has been updated with the size needed to
                                  complete the request.
**/
STATIC
EFI_STATUS
GetFileInfo (
  IN     SEMIHOST_FCB  *Fcb,
  IN OUT UINTN         *BufferSize,
  OUT    VOID          *Buffer
  )
{
  EFI_FILE_INFO   *Info = NULL;
  UINTN           NameSize = 0;
  UINTN           ResultSize;
  UINTN           Index;

  if (Fcb->IsRoot == TRUE) {
    ResultSize = SIZE_OF_EFI_FILE_INFO + sizeof(CHAR16);
  } else {
    NameSize   = AsciiStrLen (Fcb->FileName) + 1;
    ResultSize = SIZE_OF_EFI_FILE_INFO + NameSize * sizeof (CHAR16);
  }

  if (*BufferSize < ResultSize) {
    *BufferSize = ResultSize;
    return EFI_BUFFER_TOO_SMALL;
  }

  Info = Buffer;

  // Copy the current file info
  CopyMem (Info, &Fcb->Info, SIZE_OF_EFI_FILE_INFO);

  // Fill in the structure
  Info->Size = ResultSize;

  if (Fcb->IsRoot == TRUE) {
    Info->FileName[0]  = L'\0';
  } else {
    for (Index = 0; Index < NameSize; Index++) {
      Info->FileName[Index] = Fcb->FileName[Index];
    }
  }

  *BufferSize = ResultSize;

  return EFI_SUCCESS;
}

/**
  Return information about a file system.

  @param[in]      Fcb         A pointer to the description of an open file
                              which belongs to the file system, the information
                              is requested for.
  @param[in out]  BufferSize  The size, in bytes, of Buffer.
  @param[out]     Buffer      A pointer to the data buffer to return. Not NULL if
                              "*BufferSize" is greater than 0.

  @retval  EFI_SUCCESS            The information was returned.
  @retval  EFI_BUFFER_TOO_SMALL   The BufferSize is too small to return the information.
                                  BufferSize has been updated with the size needed to
                                  complete the request.

**/
STATIC
EFI_STATUS
GetFilesystemInfo (
  IN     SEMIHOST_FCB *Fcb,
  IN OUT UINTN        *BufferSize,
  OUT    VOID         *Buffer
  )
{
  EFI_FILE_SYSTEM_INFO  *Info;
  EFI_STATUS            Status;
  UINTN                 ResultSize;
  UINTN                 StringSize;

  StringSize = StrSize (mSemihostFsLabel);
  ResultSize = SIZE_OF_EFI_FILE_SYSTEM_INFO + StringSize;

  if (*BufferSize >= ResultSize) {
    ZeroMem (Buffer, ResultSize);
    Status = EFI_SUCCESS;

    Info = Buffer;

    Info->Size       = ResultSize;
    Info->ReadOnly   = FALSE;
    Info->VolumeSize = 0;
    Info->FreeSpace  = 0;
    Info->BlockSize  = 0;

    CopyMem (Info->VolumeLabel, mSemihostFsLabel, StringSize);
  } else {
    Status = EFI_BUFFER_TOO_SMALL;
  }

  *BufferSize = ResultSize;
  return Status;
}

/**
  Return information about a file or a file system.

  @param[in]      This             A pointer to the EFI_FILE_PROTOCOL instance that
                                   is the file handle the requested information is for.
  @param[in]      InformationType  The type identifier for the information being requested :
                                   EFI_FILE_INFO_ID or EFI_FILE_SYSTEM_INFO_ID or
                                   EFI_FILE_SYSTEM_VOLUME_LABEL_ID
  @param[in out]  BufferSize       The size, in bytes, of Buffer.
  @param[out]     Buffer           A pointer to the data buffer to return. The type of the
                                   data inside the buffer is indicated by InformationType.

  @retval  EFI_SUCCESS           The information was returned.
  @retval  EFI_UNSUPPORTED       The InformationType is not known.
  @retval  EFI_BUFFER_TOO_SMALL  The BufferSize is too small to return the information.
                                 BufferSize has been updated with the size needed to
                                 complete the request.
  @retval  EFI_INVALID_PARAMETER  The parameter "This" or "InformationType" or "BufferSize"
                                  is NULL or "Buffer" is NULL and "*Buffersize" is greater
                                  than 0.

**/
EFI_STATUS
FileGetInfo (
  IN     EFI_FILE  *This,
  IN     EFI_GUID  *InformationType,
  IN OUT UINTN     *BufferSize,
  OUT    VOID      *Buffer
  )
{
  SEMIHOST_FCB *Fcb;
  EFI_STATUS   Status;
  UINTN        ResultSize;

  if ((This == NULL)                         ||
      (InformationType == NULL)              ||
      (BufferSize == NULL)                   ||
      ((Buffer == NULL) && (*BufferSize > 0))  ) {
    return EFI_INVALID_PARAMETER;
  }

  Fcb = SEMIHOST_FCB_FROM_THIS(This);

  if (CompareGuid (InformationType, &gEfiFileSystemInfoGuid)) {
    Status = GetFilesystemInfo (Fcb, BufferSize, Buffer);
  } else if (CompareGuid (InformationType, &gEfiFileInfoGuid)) {
    Status = GetFileInfo (Fcb, BufferSize, Buffer);
  } else if (CompareGuid (InformationType, &gEfiFileSystemVolumeLabelInfoIdGuid)) {
    ResultSize = StrSize (mSemihostFsLabel);

    if (*BufferSize >= ResultSize) {
      CopyMem (Buffer, mSemihostFsLabel, ResultSize);
      Status = EFI_SUCCESS;
    } else {
      Status = EFI_BUFFER_TOO_SMALL;
    }

    *BufferSize = ResultSize;
  } else {
    Status = EFI_UNSUPPORTED;
  }

  return Status;
}

/**
  Set information about a file.

  @param[in]  Fcb   A pointer to the description of the open file.
  @param[in]  Info  A pointer to the file information to write.

  @retval  EFI_SUCCESS           The information was set.
  @retval  EFI_ACCESS_DENIED     An attempt is made to change the name of a file
                                 to a file that is already present.
  @retval  EFI_ACCESS_DENIED     An attempt is being made to change the
                                 EFI_FILE_DIRECTORY Attribute.
  @retval  EFI_ACCESS_DENIED     The file is a read-only file or has been
                                 opened in read-only mode and an attempt is
                                 being made to modify a field other than
                                 Attribute.
  @retval  EFI_WRITE_PROTECTED   An attempt is being made to modify a
                                 read-only attribute.
  @retval  EFI_DEVICE_ERROR      The last issued semi-hosting operation failed.
  @retval  EFI_OUT_OF_RESOURCES  A allocation needed to process the request failed.

**/
STATIC
EFI_STATUS
SetFileInfo (
  IN  SEMIHOST_FCB   *Fcb,
  IN  EFI_FILE_INFO  *Info
  )
{
  EFI_STATUS     Status;
  RETURN_STATUS  Return;
  BOOLEAN        FileSizeIsDifferent;
  BOOLEAN        FileNameIsDifferent;
  BOOLEAN        ReadOnlyIsDifferent;
  CHAR8          *AsciiFileName;
  UINTN          FileSize;
  UINTN          Length;
  UINTN          SemihostHandle;

  //
  // A directory can not be changed to a file and a file can
  // not be changed to a directory.
  //
  if (((Info->Attribute & EFI_FILE_DIRECTORY) != 0) != Fcb->IsRoot) {
    return EFI_ACCESS_DENIED;
  }

  Length = StrLen (Info->FileName) + 1;
  AsciiFileName = AllocatePool (Length);
  if (AsciiFileName == NULL) {
    return EFI_OUT_OF_RESOURCES;
  }
  UnicodeStrToAsciiStrS (Info->FileName, AsciiFileName, Length);

  FileSizeIsDifferent = (Info->FileSize != Fcb->Info.FileSize);
  FileNameIsDifferent = (AsciiStrCmp (AsciiFileName, Fcb->FileName) != 0);
  ReadOnlyIsDifferent = CompareMem (
                          &Info->CreateTime,
                          &Fcb->Info.CreateTime,
                          3 * sizeof (EFI_TIME)
                          ) != 0;

  //
  // For a read-only file or a file opened in read-only mode, only
  // the Attribute field can be modified. As the root directory is
  // read-only (i.e. VolumeOpen()), this protects the root directory
  // description.
  //
  if ((Fcb->OpenMode == EFI_FILE_MODE_READ)     ||
      (Fcb->Info.Attribute & EFI_FILE_READ_ONLY)  ) {
    if (FileSizeIsDifferent || FileNameIsDifferent || ReadOnlyIsDifferent) {
      Status = EFI_ACCESS_DENIED;
      goto Error;
    }
  }

  if (ReadOnlyIsDifferent) {
    Status = EFI_WRITE_PROTECTED;
    goto Error;
  }

  Status = EFI_DEVICE_ERROR;

  if (FileSizeIsDifferent) {
    FileSize = Info->FileSize;
    if (Fcb->Info.FileSize < FileSize) {
      Status = ExtendFile (Fcb, FileSize - Fcb->Info.FileSize);
      if (EFI_ERROR (Status)) {
        goto Error;
      }
      //
      // The read/write position from the host file system point of view
      // is at the end of the file. If the position from this module
      // point of view is smaller than the new file size, then
      // ask the host file system to move to that position.
      //
      if (Fcb->Position < FileSize) {
        FileSetPosition (&Fcb->File, Fcb->Position);
      }
    }
    Fcb->Info.FileSize = FileSize;

    Return = SemihostFileLength (Fcb->SemihostHandle, &Length);
    if (RETURN_ERROR (Return)) {
      goto Error;
    }
    Fcb->Info.PhysicalSize = Length;
  }

  //
  // Note down in RAM the Attribute field but we can not ask
  // for its modification to the host file system as the
  // semi-host interface does not provide this feature.
  //
  Fcb->Info.Attribute = Info->Attribute;

  if (FileNameIsDifferent) {
    Return = SemihostFileOpen (
               AsciiFileName,
               SEMIHOST_FILE_MODE_READ | SEMIHOST_FILE_MODE_BINARY,
               &SemihostHandle
               );
    if (!RETURN_ERROR (Return)) {
      SemihostFileClose (SemihostHandle);
      Status = EFI_ACCESS_DENIED;
      goto Error;
    }

    Return = SemihostFileRename (Fcb->FileName, AsciiFileName);
    if (RETURN_ERROR (Return)) {
      goto Error;
    }
    FreePool (Fcb->FileName);
    Fcb->FileName = AsciiFileName;
    AsciiFileName = NULL;
  }

  Status = EFI_SUCCESS;

Error:
  if (AsciiFileName != NULL) {
    FreePool (AsciiFileName);
  }

  return Status;
}

/**
  Set information about a file or a file system.

  @param[in]  This             A pointer to the EFI_FILE_PROTOCOL instance that
                               is the file handle the information is for.
  @param[in]  InformationType  The type identifier for the information being set :
                               EFI_FILE_INFO_ID or EFI_FILE_SYSTEM_INFO_ID or
                               EFI_FILE_SYSTEM_VOLUME_LABEL_ID
  @param[in]  BufferSize       The size, in bytes, of Buffer.
  @param[in]  Buffer           A pointer to the data buffer to write. The type of the
                               data inside the buffer is indicated by InformationType.

  @retval  EFI_SUCCESS            The information was set.
  @retval  EFI_UNSUPPORTED        The InformationType is not known.
  @retval  EFI_DEVICE_ERROR       The last issued semi-hosting operation failed.
  @retval  EFI_ACCESS_DENIED      An attempt is being made to change the
                                  EFI_FILE_DIRECTORY Attribute.
  @retval  EFI_ACCESS_DENIED      InformationType is EFI_FILE_INFO_ID and
                                  the file is a read-only file or has been
                                  opened in read-only mode and an attempt is
                                  being made to modify a field other than
                                  Attribute.
  @retval  EFI_ACCESS_DENIED      An attempt is made to change the name of a file
                                  to a file that is already present.
  @retval  EFI_WRITE_PROTECTED    An attempt is being made to modify a
                                  read-only attribute.
  @retval  EFI_BAD_BUFFER_SIZE    The size of the buffer is lower than that indicated by
                                  the data inside the buffer.
  @retval  EFI_OUT_OF_RESOURCES   An allocation needed to process the request failed.
  @retval  EFI_INVALID_PARAMETER  At least one of the parameters is invalid.

**/
EFI_STATUS
FileSetInfo (
  IN EFI_FILE  *This,
  IN EFI_GUID  *InformationType,
  IN UINTN     BufferSize,
  IN VOID      *Buffer
  )
{
  SEMIHOST_FCB          *Fcb;
  EFI_FILE_INFO         *Info;
  EFI_FILE_SYSTEM_INFO  *SystemInfo;
  CHAR16                *VolumeLabel;

  if ((This == NULL) || (InformationType == NULL) || (Buffer == NULL)) {
    return EFI_INVALID_PARAMETER;
  }

  Fcb = SEMIHOST_FCB_FROM_THIS (This);

  if (CompareGuid (InformationType, &gEfiFileInfoGuid)) {
    Info = Buffer;
    if (Info->Size < (SIZE_OF_EFI_FILE_INFO + StrSize (Info->FileName))) {
      return EFI_INVALID_PARAMETER;
    }
    if (BufferSize < Info->Size) {
      return EFI_BAD_BUFFER_SIZE;
    }
    return SetFileInfo (Fcb, Info);
  } else if (CompareGuid (InformationType, &gEfiFileSystemInfoGuid)) {
    SystemInfo = Buffer;
    if (SystemInfo->Size <
        (SIZE_OF_EFI_FILE_SYSTEM_INFO + StrSize (SystemInfo->VolumeLabel))) {
      return EFI_INVALID_PARAMETER;
    }
    if (BufferSize < SystemInfo->Size) {
      return EFI_BAD_BUFFER_SIZE;
    }
    Buffer = SystemInfo->VolumeLabel;

    if (StrSize (Buffer) > 0) {
      VolumeLabel = AllocateCopyPool (StrSize (Buffer), Buffer);
      if (VolumeLabel != NULL) {
        FreePool (mSemihostFsLabel);
        mSemihostFsLabel = VolumeLabel;
        return EFI_SUCCESS;
      } else {
        return EFI_OUT_OF_RESOURCES;
      }
    } else {
      return EFI_INVALID_PARAMETER;
    }
  } else if (!CompareGuid (InformationType, &gEfiFileSystemVolumeLabelInfoIdGuid)) {
    return EFI_UNSUPPORTED;
  } else {
    return EFI_UNSUPPORTED;
  }
}

EFI_STATUS
FileFlush (
  IN EFI_FILE *File
  )
{
  SEMIHOST_FCB *Fcb;

  Fcb = SEMIHOST_FCB_FROM_THIS(File);

  if (Fcb->IsRoot) {
    return EFI_SUCCESS;
  } else {
    if ((Fcb->Info.Attribute & EFI_FILE_READ_ONLY)
        || !(Fcb->OpenMode & EFI_FILE_MODE_WRITE)) {
      return EFI_ACCESS_DENIED;
    } else {
      return EFI_SUCCESS;
    }
  }
}

EFI_STATUS
SemihostFsEntryPoint (
  IN EFI_HANDLE           ImageHandle,
  IN EFI_SYSTEM_TABLE     *SystemTable
  )
{
  EFI_STATUS    Status;

  Status = EFI_NOT_FOUND;

  if (SemihostConnectionSupported ()) {
    mSemihostFsLabel = AllocateCopyPool (StrSize (DEFAULT_SEMIHOST_FS_LABEL), DEFAULT_SEMIHOST_FS_LABEL);
    if (mSemihostFsLabel == NULL) {
      return EFI_OUT_OF_RESOURCES;
    }

    Status = gBS->InstallMultipleProtocolInterfaces (
                    &gInstallHandle,
                    &gEfiSimpleFileSystemProtocolGuid, &gSemihostFs,
                    &gEfiDevicePathProtocolGuid,       &gDevicePath,
                    NULL
                    );

    if (EFI_ERROR(Status)) {
      FreePool (mSemihostFsLabel);
    }
  }

  return Status;
}