_Check_return_
NTSTATUS
LcGetRegistryValueDWord(
_In_ PUNICODE_STRING RegistryPath,
_In_ PUNICODE_STRING RegistryValueName,
_Out_ PULONG Value
)
/*++
Summary:
This function reads a REG_DWORD value from the path given.
Arguments:
RegistryPath - Path to the registry value to be read.
RegistryValueName - Registry value name, which value to read.
Value - A pointer to a ULONG variable that receives the DWORD value read.
Return value:
The return value is the status of the operation.
--*/
{
NTSTATUS status = STATUS_SUCCESS;
PKEY_VALUE_PARTIAL_INFORMATION valueBuffer = NULL;
PAGED_CODE();
// Other parameters will be validated in the 'LcGetRegistryValue' function.
IF_FALSE_RETURN_RESULT(Value != NULL, STATUS_INVALID_PARAMETER_3);
__try
{
NT_IF_FAIL_LEAVE(LcGetRegistryValue(RegistryPath, RegistryValueName, &valueBuffer));
// We are expecting a DWORD value.
NT_IF_FALSE_LEAVE(valueBuffer->Type == REG_DWORD, STATUS_INVALID_PARAMETER);
*Value = *(PULONG)&valueBuffer->Data;
}
__finally
{
if (valueBuffer != NULL)
{
LcFreeNonPagedBuffer(valueBuffer);
}
}
return status;
}
static
_Check_return_
NTSTATUS
LcFetchFileByChunks (
_In_ PCFLT_RELATED_OBJECTS FltObjects,
_In_ HANDLE SourceFileHandle,
_In_ PLARGE_INTEGER SourceFileSize,
_Out_ PLARGE_INTEGER BytesCopied
)
/*++
Summary:
This function copies the original file from the 'SourceFileHandle' to the currently opened
file ('FltObjects->FileObject') by chunks.
It maintains its own list of chunks, and extends it, if there are no chunks available to read into.
Write operation goes from one chunk to another in a sequential order. If the next chunk is empty,
write waits for the read to be completed, and proceeds.
There are simple rules for chunks allocation:
1. Up to two chunks are initially allocated:
a) If the file is smaller than the 'ChunkSize', only one chunk is allocated with buffer
that is equal to the file size.
b) If the file is larger than the 'ChunkSize', two chunks are allocated, taking the
file size into account for the second chunk size.
2. If all chunks currently allocated are full and awaiting to be written to a disk, and
the current amount of chunks is lesser than 'MaxChunks', an additional chunk is allocated.
There is a corner case, when the actual file size differs from the reported one. In this case
one of the chunks in the list will be smaller than the 'ChunkSize'.
For example, 'MaxChunks' is 3, ChunkSize is '10', file size reported is '12', and actual file
size is '25'.
Two chunks will be initially allocated: [1] 10b; [2] (12-10)=2b.
Later on, when all of them will be filled in with the data, and EOF will not be received,
because the actual size is 25b, another chunk [3] of size 10b (ChunkSize) will be allocated.
In total, there will be three chunks: 10b, 2b, and 10b.
We don't reallocate the 2nd chunk, because this driver is supposed to be used with a proper
filesystems, but making this modification might be a valuable TODO item.
Let's look at how chunks work.
All chunks are stored in the doubly-linked list. [Head] node doesn't contain any buffer to
store data in. Refer to the 'FILE_CHUNK' structure for details.
MSDN about lists: http://msdn.microsoft.com/en-us/library/windows/hardware/ff563802(v=vs.85).aspx
For large files we will have two chunks from the beginning.
[Head] <-> [1] <-> [2] <-> [Head]
There are pointers for [R]ead and [W]rite.
When the first chunk is being read, the list will look like the following:
[Head] <-> [1] <-> [2] <-> [Head]
[W] [R]
[W] is awaiting for the [1] to be filled in with the data before writing it to the disk.
When the [1] chunk is filled with the data:
[Head] <-> [1*] <-> [2] <-> [Head]
[W] [R]
[1] is full and is being written to a disk, and we're reading into chunk [2].
Let's also assume that the reads are faster then writes. When the [2] chunk is
full, there are no free chunks available:
[Head] <-> [1*] <-> [2*] <-> [Head]
[W] [R]
If the current amount of chunks is lesser than the 'MaxChunks' value, a new chunk will be
allocated before the next [R] node. In this case it will be added before [Head] to the end
of the list, and read will continue:
[Head] <-> [1*] <-> [2*] <-> [3] <-> [Head]
[W] [R]
Then [W] and [R] finish, and [W] moves to the [2] chunk.
[Head] <-> [1] <-> [2*] <-> [3*] <-> [Head]
[W] [R]
[R] sees that [1] chunk is available, and reads into it:
[Head] <-> [1] <-> [2*] <-> [3*] <-> [Head]
[R] [W]
After [R] finishes reading, there are no free chunks again:
[Head] <-> [1*] <-> [2*] <-> [3*] <-> [Head]
[R] [W]
A new chunk can be allocated again before the [2]:
[Head] <-> [1*] <-> [4] <-> [2*] <-> [3*] <-> [Head]
[R] [W]
With this approach, [R] will fill chunks [1]->[2]->[3]->[1]->[4], and write will
write them in the same order.
I.e. allocating a new chunk before the next filled chunk (if the amount of chunks
is lesser than the 'MaxChunks') makes sure that the data is written sequentially,
and there is no need to constantly seek in the file.
Arguments:
FltObjects - Pointer to the 'FLT_RELATED_OBJECTS' data structure containing
opaque handles to this filter, instance, its associated volume and
file object.
SourceFileHandle - Handle to the source file to copy content from.
SourceFileSize - Size of the source file.
BytesCopied - Pointer to the LARGE_INTEGER structure that receives the amount
of bytes copied.
Return Value:
The return value is the status of the operation.
--*/
{
NTSTATUS status = STATUS_SUCCESS;
LIST_ENTRY chunksListHead = { 0 };
ULONG chunkListLength = 0;
// State of the R/W operations.
BOOLEAN readComplete = FALSE;
BOOLEAN writeComplete = FALSE;
PFILE_CHUNK readChunk = NULL;
PFILE_CHUNK writeChunk = NULL;
BOOLEAN eof = FALSE;
BOOLEAN waitingForRead = FALSE;
KEVENT writeEvent = { 0 };
WRITE_CALLBACK_CONTEXT writeCallbackContext = { 0 };
LARGE_INTEGER waitTimeout = { 0 };
LARGE_INTEGER zeroTimeout = { 0 };
IO_STATUS_BLOCK statusBlock = { 0 };
LARGE_INTEGER remainingBytes = { 0 };
LARGE_INTEGER totalBytesRead = { 0 };
LARGE_INTEGER totalBytesWritten = { 0 };
LARGE_INTEGER sourceFileOffset = { 0 };
LARGE_INTEGER destinationFileOffset = { 0 };
PAGED_CODE();
FLT_ASSERT(FltObjects != NULL);
FLT_ASSERT(SourceFileHandle != NULL);
FLT_ASSERT(SourceFileSize != NULL);
FLT_ASSERT(SourceFileSize->QuadPart > 0);
FLT_ASSERT(BytesCopied != NULL);
FLT_ASSERT(KeGetCurrentIrql() == PASSIVE_LEVEL);
*BytesCopied = RtlConvertLongToLargeInteger(0);
__try
{
// Set the relative timeout (1 stands for 100 nanoseconds).
waitTimeout = RtlConvertLongToLargeInteger(-10000);
waitTimeout.QuadPart *= TimeoutMilliseconds;
KeInitializeEvent(&writeEvent, NotificationEvent, TRUE);
writeCallbackContext.Event = &writeEvent;
remainingBytes.QuadPart = SourceFileSize->QuadPart;
NT_IF_FAIL_LEAVE(LcInitializeChunksList(FltObjects->Instance, &chunksListHead, remainingBytes, &chunkListLength));
for (;;)
{
if (waitingForRead)
{
// Wait for the read operation to finish.
NT_IF_FAIL_LEAVE(ZwWaitForSingleObject(SourceFileHandle, FALSE, &waitTimeout));
readComplete = TRUE;
}
else
{
readComplete = ZwWaitForSingleObject(SourceFileHandle, FALSE, &zeroTimeout) == STATUS_SUCCESS;
}
writeComplete = KeReadStateEvent(&writeEvent) != 0;
if (!eof && readComplete)
{
// If it's not the first read, update status of the current chunk.
if (readChunk != NULL)
{
status = statusBlock.Status;
if (NT_SUCCESS(status) || status == STATUS_END_OF_FILE)
{
ULONG bytesRead = (ULONG)statusBlock.Information;
readChunk->BytesInBuffer = bytesRead;
remainingBytes.QuadPart -= bytesRead;
totalBytesRead.QuadPart += bytesRead;
sourceFileOffset.QuadPart += bytesRead;
if (status == STATUS_END_OF_FILE || bytesRead < readChunk->BufferSize)
{
eof = TRUE;
status = STATUS_SUCCESS;
// Will not be used later in this case, only to have the proper data here.
remainingBytes.QuadPart = 0;
}
}
NT_IF_FAIL_LEAVE(status);
}
// Move to the next available chunk and schedule read.
if (!eof)
{
// If the remote file system returned an invalid file size, when we started reading it,
// this value might be negative. Set it to the default, so the newly allocated chunk
// will have the maximum allowed size.
if (remainingBytes.QuadPart <= 0)
{
remainingBytes.QuadPart = ChunkSize;
}
NT_IF_FAIL_LEAVE(LcGetNextAvailableChunk(
FltObjects->Instance,
&chunksListHead,
&readChunk,
&chunkListLength,
TRUE, // Read operation.
&remainingBytes,
&writeEvent,
&waitTimeout));
// Schedule read operation for the current chunk.
status = ZwReadFile(
SourceFileHandle,
NULL,
NULL,
NULL,
&statusBlock,
readChunk->Buffer,
readChunk->BufferSize,
&sourceFileOffset,
NULL);
NT_IF_FALSE_LEAVE(status == STATUS_PENDING || status == STATUS_SUCCESS, status);
}
}
if (writeComplete)
{
if (!waitingForRead)
{
// If it's not the first write, update status of the current chunk.
if (writeChunk != NULL)
{
NT_IF_FAIL_LEAVE(writeCallbackContext.Status);
writeChunk->BytesInBuffer = 0;
totalBytesWritten.QuadPart += writeCallbackContext.BytesWritten;
destinationFileOffset.QuadPart += writeCallbackContext.BytesWritten;
}
NT_IF_FAIL_LEAVE(LcGetNextAvailableChunk(
FltObjects->Instance,
&chunksListHead,
&writeChunk,
&chunkListLength,
FALSE, // Write operation.
NULL,
NULL,
NULL));
}
waitingForRead = FALSE;
// If we don't have any data in the current chunk, restart from the beginning of the loop.
if (writeChunk->BytesInBuffer == 0)
{
if (eof)
{
// We're done!
break;
}
else
{
// Since we're waiting for the read to complete for the current chunk,
// don't change the chunk position on next iteration.
waitingForRead = TRUE;
continue;
}
}
KeClearEvent(&writeEvent);
NT_IF_FAIL_LEAVE(FltWriteFile(
FltObjects->Instance,
FltObjects->FileObject,
&destinationFileOffset,
writeChunk->BytesInBuffer,
writeChunk->Buffer,
FLTFL_IO_OPERATION_DO_NOT_UPDATE_BYTE_OFFSET,
NULL,
(PFLT_COMPLETED_ASYNC_IO_CALLBACK)&LcWriteCallback,
&writeCallbackContext));
}
}
*BytesCopied = totalBytesWritten;
}
__finally
{
LcClearChunksList(FltObjects->Instance, &chunksListHead);
}
return status;
}
_Check_return_
NTSTATUS
LcGetRegistryValueString(
_In_ PUNICODE_STRING RegistryPath,
_In_ PUNICODE_STRING RegistryValueName,
_Out_ PUNICODE_STRING Value
)
/*++
Summary:
This function reads REG_MULTI_SZ or REG_SZ value from the path given.
Caller should manually free the string received using the 'LcFreeUnicodeString' function.
Arguments:
RegistryPath - Path to the registry value to be read.
RegistryValueName - Registry value name, which value to read.
Value - A pointer to a unicode string that receives the value.
Return value:
The return value is the status of the operation.
--*/
{
NTSTATUS status = STATUS_SUCCESS;
PKEY_VALUE_PARTIAL_INFORMATION valueBuffer = NULL;
UNICODE_STRING string = { 0 };
PAGED_CODE();
// Other parameters will be validated in the 'LcGetRegistryValue' function.
IF_FALSE_RETURN_RESULT(Value != NULL, STATUS_INVALID_PARAMETER_3);
__try
{
NT_IF_FAIL_LEAVE(LcGetRegistryValue(RegistryPath, RegistryValueName, &valueBuffer));
// We are expecting REG_MULTI_SZ or REG_SZ value.
NT_IF_FALSE_LEAVE(valueBuffer->Type == REG_MULTI_SZ || valueBuffer->Type == REG_SZ, STATUS_INVALID_PARAMETER);
// Allocate internal string buffer and copy the value there.
NT_IF_FAIL_LEAVE(LcAllocateUnicodeString(&string, (USHORT)valueBuffer->DataLength));
__analysis_assume(string.Buffer != NULL);
RtlCopyMemory(string.Buffer, &valueBuffer->Data, valueBuffer->DataLength);
string.Length = (USHORT)valueBuffer->DataLength - sizeof(WCHAR);
// Set the output value and set the 'string.Buffer' to NULL, so it won't be freed in the __finally block.
*Value = string;
string.Buffer = NULL;
}
__finally
{
if (valueBuffer != NULL)
{
LcFreeNonPagedBuffer(valueBuffer);
}
if (string.Buffer != NULL)
{
LcFreeUnicodeString(&string);
}
}
return status;
}
