Why IRP_MJ_WRITE not trigger when do the file compressing?

Welcome, fellow developers! If you’re reading this, chances are you’re stuck on a pesky issue: IRP_MJ_WRITE not triggering when compressing files. Don’t worry; we’ve got you covered. In this article, we’ll dive deep into the world of IRP major functions, file compression, and Windows kernel-mode drivers. Buckle up, and let’s get started!

What is IRP_MJ_WRITE?

IRP_MJ_WRITE is a major function code used in Windows kernel-mode drivers to request write access to a file or device. When a user application or another driver initiates a write operation, the I/O manager creates an I/O request packet (IRP) and assigns it an IRP_MJ_WRITE major function code. This IRP is then sent to the driver, which is responsible for processing the write operation.

NTSTATUS
DrvDispatch(
    PDEVICE_OBJECT DeviceObject,
    PIRP Irp
)
{
    // ...
    switch (Irp->MajorFunction) {
        case IRP_MJ_WRITE:
            // Process the write operation
            break;
        // ...
    }
    return STATUS_SUCCESS;
}

What is file compression?

File compression is a process that reduces the size of a file by encoding its data using various algorithms, making it more efficient for storage or transmission. Common file compression formats include ZIP, RAR, and 7-ZIP. When compressing a file, the compression algorithm reads the original file, compresses its data, and writes the compressed data to a new file or output stream.

// Example of compressing a file using the zlib library
z_stream strm;
strm.zalloc = Z_NULL;
strm.zfree = Z_NULL;
strm.opaque = Z_NULL;

inflateInit(&strm);
FILE *fp = fopen("original_file.txt", "rb");
FILE *fp_compressed = fopen("compressed_file.zip", "wb");

char buffer[1024];
while (!feof(fp)) {
    fread(buffer, 1, 1024, fp);
    strm.avail_in = 1024;
    strm.next_in = buffer;
    do {
        strm.avail_out = 1024;
        strm.next_out = buffer;
        inflate(&strm, Z_NO_FLUSH);
        fwrite(buffer, 1, 1024 - strm.avail_out, fp_compressed);
    } while (strm.avail_out == 0);
}

inflateEnd(&strm);
fclose(fp);
fclose(fp_compressed);

The Mystery of IRP_MJ_WRITE not Triggering

So, why doesn’t IRP_MJ_WRITE trigger when compressing files? Let’s explore the possible reasons:

• Buffering and caching: When compressing a file, the compression algorithm often uses buffering and caching to improve performance. This can lead to the IRP_MJ_WRITE not being sent to the driver immediately, as the compressed data is stored in memory or temporary files instead of being written directly to the disk.
• Intermediate file creation: Compression algorithms might create temporary files or intermediate files during the compression process. These files might not trigger IRP_MJ_WRITE, as they are not the final compressed file.
• File handle and streaming: When compressing a file, the compression algorithm might use a separate file handle for reading and writing, or use streaming APIs (e.g., ReadFile and WriteFile) instead of traditional file I/O functions. This can bypass the IRP_MJ_WRITE major function code.
• Driver and file system interactions: The Windows file system and kernel-mode drivers interact in complex ways. It’s possible that the file compression process interacts with the file system in a way that prevents IRP_MJ_WRITE from being triggered.

Solutions and Workarounds

Now that we’ve explored the possible reasons behind IRP_MJ_WRITE not triggering, let’s discuss some solutions and workarounds:

1. Use IRP_MJ_CLEANUP instead

In some cases, you can use IRP_MJ_CLEANUP to detect when a file is being closed or cleaned up after compression. This might not provide the same level of control as IRP_MJ_WRITE, but it can be a viable alternative.

NTSTATUS
DrvDispatch(
    PDEVICE_OBJECT DeviceObject,
    PIRP Irp
)
{
    // ...
    switch (Irp->MajorFunction) {
        case IRP_MJ_CLEANUP:
            // Process the file cleanup
            break;
        // ...
    }
    return STATUS_SUCCESS;
}

2. Monitor file system events

Another approach is to monitor file system events using APIs like ReadDirectoryChangesW or ReadDirectoryChangesExW. This can help you detect when a file is being compressed or modified.

HANDLE hDir = CreateFile(
    "C:\\Path\\To\\Directory",
    GENERIC_READ,
    FILE_SHARE_READ | FILE_SHARE_WRITE,
    NULL,
    OPEN_EXISTING,
    FILE_FLAG_BACKUP_SEMANTICS,
    NULL
);

BYTE buffer[1024];
DWORD dwBytesReturned;
while (ReadDirectoryChangesW(
    hDir,
    &buffer,
    1024,
    TRUE,
    FILE_NOTIFY_CHANGE_LAST_WRITE,
    &dwBytesReturned,
    NULL,
    NULL)
) {
    // Process the file system event
}

3. Implement a custom file compression filter driver

A more advanced solution is to develop a custom file compression filter driver that intercepts and processes IRP_MJ_WRITE requests. This allows you to have fine-grained control over the compression process and trigger IRP_MJ_WRITE as needed.

NTSTATUS
CompressionFilterDispatch(
    PDEVICE_OBJECT DeviceObject,
    PIRP Irp
)
{
    // ...
    switch (Irp->MajorFunction) {
        case IRP_MJ_WRITE:
            // Process the write operation and trigger compression
            break;
        // ...
    }
    return STATUS_SUCCESS;
}

Conclusion

In conclusion, the mystery of IRP_MJ_WRITE not triggering during file compression is a complex issue with multiple possible causes and solutions. By understanding the underlying mechanisms and interactions between the file system, kernel-mode drivers, and compression algorithms, you can develop effective workarounds and solutions to overcome this challenge.

Reason	Solution
Buffering and caching	Monitor file system events or implement a custom file compression filter driver
Intermediate file creation	Use IRP_MJ_CLEANUP or monitor file system events
File handle and streaming	Implement a custom file compression filter driver or use IRP_MJ_CLEANUP
Driver and file system interactions	Monitor file system events or implement a custom file compression filter driver

We hope this article has provided you with the insights and guidance you need to tackle the IRP_MJ_WRITE mystery. Happy coding, and may the kernel-mode driver force be with you!

Frequently Asked Question

When compressing files, why does IRP_MJ_WRITE not trigger? Here are some possible reasons why: