/*
 * COPYRIGHT:        See COPYING in the top level directory
 * PROJECT:          ReactOS kernel
 * FILE:             drivers/fs/vfat/rw.c
 * PURPOSE:          VFAT Filesystem
 * PROGRAMMER:       Jason Filby (jasonfilby@yahoo.com)
 *
 */

/* INCLUDES *****************************************************************/

#define NDEBUG
#include "vfat.h"

/*
 * Uncomment to enable strict verification of cluster/offset pair
 * caching. If this option is enabled you lose all the benefits of
 * the caching and the read/write operations will actually be
 * slower. It's meant only for debugging!!!
 * - Filip Navara, 26/07/2004
 */
/* #define DEBUG_VERIFY_OFFSET_CACHING */

/* FUNCTIONS *****************************************************************/

NTSTATUS
NextCluster(PDEVICE_EXTENSION DeviceExt,
	    ULONG FirstCluster,
	    PULONG CurrentCluster,
	    BOOLEAN Extend)
     /*
      * Return the next cluster in a FAT chain, possibly extending the chain if
      * necessary
      */
{
 if (FirstCluster == 1)
    {
      (*CurrentCluster) += DeviceExt->FatInfo.SectorsPerCluster;
      return(STATUS_SUCCESS);
    }
  else
    {
      if (Extend)
        return GetNextClusterExtend(DeviceExt, (*CurrentCluster), CurrentCluster);
      else
        return GetNextCluster(DeviceExt, (*CurrentCluster), CurrentCluster);
    }
}

NTSTATUS
OffsetToCluster(PDEVICE_EXTENSION DeviceExt,
		ULONG FirstCluster,
		ULONG FileOffset,
		PULONG Cluster,
		BOOLEAN Extend)
     /*
      * Return the cluster corresponding to an offset within a file,
      * possibly extending the file if necessary
      */
{
  ULONG CurrentCluster;
  ULONG i;
  NTSTATUS Status;
/*
  DPRINT("OffsetToCluster(DeviceExt %x, Fcb %x, FirstCluster %x,"
         " FileOffset %x, Cluster %x, Extend %d)\n", DeviceExt,
         Fcb, FirstCluster, FileOffset, Cluster, Extend);
*/
  if (FirstCluster == 0)
  {
    DbgPrint("OffsetToCluster is called with FirstCluster = 0!\n");
    KEBUGCHECK(0);
  }

  if (FirstCluster == 1)
    {
      /* root of FAT16 or FAT12 */
      *Cluster = DeviceExt->FatInfo.rootStart + FileOffset
	/ (DeviceExt->FatInfo.BytesPerCluster) * DeviceExt->FatInfo.SectorsPerCluster;
      return(STATUS_SUCCESS);
    }
  else
    {
      CurrentCluster = FirstCluster;
      if (Extend)
        {
          for (i = 0; i < FileOffset / DeviceExt->FatInfo.BytesPerCluster; i++)
            {
              Status = GetNextClusterExtend (DeviceExt, CurrentCluster, &CurrentCluster);
              if (!NT_SUCCESS(Status))
                return(Status);
    	    }
          *Cluster = CurrentCluster;
       }
     else
        {
          for (i = 0; i < FileOffset / DeviceExt->FatInfo.BytesPerCluster; i++)
            {
              Status = GetNextCluster (DeviceExt, CurrentCluster, &CurrentCluster);
              if (!NT_SUCCESS(Status))
                return(Status);
    	    }
          *Cluster = CurrentCluster;
       }
     return(STATUS_SUCCESS);
   }
}

static NTSTATUS
VfatReadFileData (PVFAT_IRP_CONTEXT IrpContext,
                  ULONG Length,
		  LARGE_INTEGER ReadOffset,
		  PULONG LengthRead)
/*
 * FUNCTION: Reads data from a file
 */
{
  ULONG CurrentCluster;
  ULONG FirstCluster;
  ULONG StartCluster;
  ULONG ClusterCount;
  LARGE_INTEGER StartOffset;
  PDEVICE_EXTENSION DeviceExt;
  BOOLEAN First = TRUE;
  PVFATFCB Fcb;
  PVFATCCB Ccb;
  NTSTATUS Status;
  ULONG BytesDone;
  ULONG BytesPerSector;
  ULONG BytesPerCluster;
  ULONG LastCluster;
  ULONG LastOffset;

  /* PRECONDITION */
  ASSERT(IrpContext);
  DeviceExt = IrpContext->DeviceExt;
  ASSERT(DeviceExt);
  ASSERT(DeviceExt->FatInfo.BytesPerCluster);
  ASSERT(IrpContext->FileObject);
  ASSERT(IrpContext->FileObject->FsContext2 != NULL);

  DPRINT("VfatReadFileData(DeviceExt %x, FileObject %x, "
	 "Length %d, ReadOffset 0x%I64x)\n", DeviceExt,
	 IrpContext->FileObject, Length, ReadOffset.QuadPart);

  *LengthRead = 0;

  Ccb = (PVFATCCB)IrpContext->FileObject->FsContext2;
  Fcb = IrpContext->FileObject->FsContext;
  BytesPerSector = DeviceExt->FatInfo.BytesPerSector;
  BytesPerCluster = DeviceExt->FatInfo.BytesPerCluster;

  ASSERT(ReadOffset.QuadPart + Length <= ROUND_UP(Fcb->RFCB.FileSize.QuadPart, BytesPerSector));
  ASSERT(ReadOffset.u.LowPart % BytesPerSector == 0);
  ASSERT(Length % BytesPerSector == 0);

  /* Is this a read of the FAT? */
  if (Fcb->Flags & FCB_IS_FAT)
  {
    ReadOffset.QuadPart += DeviceExt->FatInfo.FATStart * BytesPerSector;
    Status = VfatReadDiskPartial(IrpContext, &ReadOffset, Length, 0, TRUE);

    if (NT_SUCCESS(Status))
    {
      *LengthRead = Length;
    }
    else
    {
      DPRINT1("FAT reading failed, Status %x\n", Status);
    }
    return Status;
  }
  /* Is this a read of the Volume ? */
  if (Fcb->Flags & FCB_IS_VOLUME)
  {
    Status = VfatReadDiskPartial(IrpContext, &ReadOffset, Length, 0, TRUE);
    if (NT_SUCCESS(Status))
    {
      *LengthRead = Length;
    }
    else
    {
      DPRINT1("Volume reading failed, Status %x\n", Status);
    }
    return Status;
  }

  /*
   * Find the first cluster
   */
  FirstCluster = CurrentCluster =
    vfatDirEntryGetFirstCluster (DeviceExt, &Fcb->entry);

  if (FirstCluster == 1)
  {
    // Directory of FAT12/16 needs a special handling
    CHECKPOINT;
    if (ReadOffset.u.LowPart + Length > DeviceExt->FatInfo.rootDirectorySectors * BytesPerSector)
    {
      Length = DeviceExt->FatInfo.rootDirectorySectors * BytesPerSector - ReadOffset.u.LowPart;
    }
    ReadOffset.u.LowPart += DeviceExt->FatInfo.rootStart * BytesPerSector;

    // Fire up the read command

    Status = VfatReadDiskPartial (IrpContext, &ReadOffset, Length, 0, TRUE);
    if (NT_SUCCESS(Status))
    {
      *LengthRead = Length;
    }
    return Status;
  }

  ExAcquireFastMutex(&Fcb->LastMutex);
  LastCluster = Fcb->LastCluster;
  LastOffset = Fcb->LastOffset;
  ExReleaseFastMutex(&Fcb->LastMutex);

  /*
   * Find the cluster to start the read from
   */
  if (LastCluster > 0 && ReadOffset.u.LowPart >= LastOffset)
  {
    Status = OffsetToCluster(DeviceExt, LastCluster,
                             ROUND_DOWN(ReadOffset.u.LowPart, BytesPerCluster) -
                             LastOffset,
                             &CurrentCluster, FALSE);
#ifdef DEBUG_VERIFY_OFFSET_CACHING
    /* DEBUG VERIFICATION */
    {
      ULONG CorrectCluster;
      OffsetToCluster(DeviceExt, FirstCluster,
                      ROUND_DOWN(ReadOffset.u.LowPart, BytesPerCluster),
                      &CorrectCluster, FALSE);
      if (CorrectCluster != CurrentCluster)
        KEBUGCHECK(FAT_FILE_SYSTEM);
    }
#endif
  }
  else
  {
    Status = OffsetToCluster(DeviceExt, FirstCluster,
                             ROUND_DOWN(ReadOffset.u.LowPart, BytesPerCluster),
                             &CurrentCluster, FALSE);
  }
  if (!NT_SUCCESS(Status))
  {
    return(Status);
  }

  ExAcquireFastMutex(&Fcb->LastMutex);
  Fcb->LastCluster = CurrentCluster;
  Fcb->LastOffset = ROUND_DOWN (ReadOffset.u.LowPart, BytesPerCluster);
  ExReleaseFastMutex(&Fcb->LastMutex);

  KeInitializeEvent(&IrpContext->Event, NotificationEvent, FALSE);
  IrpContext->RefCount = 1;

  while (Length > 0 && CurrentCluster != 0xffffffff)
  {
    StartCluster = CurrentCluster;
    StartOffset.QuadPart = ClusterToSector(DeviceExt, StartCluster) * BytesPerSector;
    BytesDone = 0;
    ClusterCount = 0;

    do
    {
      ClusterCount++;
      if (First)
      {
        BytesDone =  min (Length, BytesPerCluster - (ReadOffset.u.LowPart % BytesPerCluster));
      	StartOffset.QuadPart += ReadOffset.u.LowPart % BytesPerCluster;
      	First = FALSE;
      }
      else
      {
      	if (Length - BytesDone > BytesPerCluster)
      	{
      	  BytesDone += BytesPerCluster;
      	}
      	else
      	{
      	  BytesDone = Length;
      	}
      }
      Status = NextCluster(DeviceExt, FirstCluster, &CurrentCluster, FALSE);
    }
    while (StartCluster + ClusterCount == CurrentCluster && NT_SUCCESS(Status) && Length > BytesDone);
    DPRINT("start %08x, next %08x, count %d\n",
           StartCluster, CurrentCluster, ClusterCount);

    ExAcquireFastMutex(&Fcb->LastMutex);
    Fcb->LastCluster = StartCluster + (ClusterCount - 1);
    Fcb->LastOffset = ROUND_DOWN(ReadOffset.u.LowPart, BytesPerCluster) + (ClusterCount - 1) * BytesPerCluster;
    ExReleaseFastMutex(&Fcb->LastMutex);

    // Fire up the read command
    Status = VfatReadDiskPartial (IrpContext, &StartOffset, BytesDone, *LengthRead, FALSE);
    if (!NT_SUCCESS(Status) && Status != STATUS_PENDING)
      {
        break;
      }
    *LengthRead += BytesDone;
    Length -= BytesDone;
    ReadOffset.u.LowPart += BytesDone;
  }
  if (0 != InterlockedDecrement((PLONG)&IrpContext->RefCount))
    {
      KeWaitForSingleObject(&IrpContext->Event, Executive, KernelMode, FALSE, NULL);
    }
  if (NT_SUCCESS(Status) || Status == STATUS_PENDING)
    {
      if (Length > 0)
        {
	  Status = STATUS_UNSUCCESSFUL;
	}
      else
        {
          Status = IrpContext->Irp->IoStatus.Status;
	}
    }
  return Status;
}

static NTSTATUS
VfatWriteFileData(PVFAT_IRP_CONTEXT IrpContext,
		  ULONG Length,
		  LARGE_INTEGER WriteOffset)
{
   PDEVICE_EXTENSION DeviceExt;
   PVFATFCB Fcb;
   PVFATCCB Ccb;
   ULONG Count;
   ULONG FirstCluster;
   ULONG CurrentCluster;
   ULONG BytesDone;
   ULONG StartCluster;
   ULONG ClusterCount;
   NTSTATUS Status = STATUS_SUCCESS;
   BOOLEAN First = TRUE;
   ULONG BytesPerSector;
   ULONG BytesPerCluster;
   LARGE_INTEGER StartOffset;
   ULONG BufferOffset;
   ULONG LastCluster;
   ULONG LastOffset;

   /* PRECONDITION */
   ASSERT(IrpContext);
   DeviceExt = IrpContext->DeviceExt;
   ASSERT(DeviceExt);
   ASSERT(DeviceExt->FatInfo.BytesPerCluster);
   ASSERT(IrpContext->FileObject);
   ASSERT(IrpContext->FileObject->FsContext2 != NULL);

   Ccb = (PVFATCCB)IrpContext->FileObject->FsContext2;
   Fcb = IrpContext->FileObject->FsContext;
   BytesPerCluster = DeviceExt->FatInfo.BytesPerCluster;
   BytesPerSector = DeviceExt->FatInfo.BytesPerSector;

   DPRINT("VfatWriteFileData(DeviceExt %x, FileObject %x, "
	  "Length %d, WriteOffset 0x%I64x), '%wZ'\n", DeviceExt,
	  IrpContext->FileObject, Length, WriteOffset,
	  &Fcb->PathNameU);