如何用C#代码实现快速查询文件
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相信使用过Everything的人都对其超快的搜索速度印象非常深刻，它的主要原理是通过扫描NTFS磁盘的USN Journal读取的文件列表，而不是磁盘目录，由于USN Journal非常小，因此能实现快速搜索。
由于.Net程序的Dll基本上是通用的，在C#中也可以直接使用它。
public class MFTScanner
{
private static IntPtr INVALID_HANDLE_VALUE = new IntPtr(-1);
private const uint GENERIC_READ = 0x80000000;
private const int FILE_SHARE_READ = 0x1;
private const int FILE_SHARE_WRITE = 0x2;
private const int OPEN_EXISTING = 3;
private const int FILE_READ_ATTRIBUTES = 0x80;
private const int FILE_NAME_IINFORMATION = 9;
private const int FILE_FLAG_BACKUP_SEMANTICS = 0x2000000;
private const int FILE_OPEN_FOR_BACKUP_INTENT = 0x4000;
private const int FILE_OPEN_BY_FILE_ID = 0x2000;
private const int FILE_OPEN = 0x1;
private const int OBJ_CASE_INSENSITIVE = 0x40;
private const int FSCTL_ENUM_USN_DATA = 0x900b3;
[StructLayout(LayoutKind.Sequential)]
private struct MFT_ENUM_DATA
{
public long StartFileReferenceNumber;
public long LowUsn;
public long HighUsn;
}
[StructLayout(LayoutKind.Sequential)]
private struct USN_RECORD
{
public int RecordLength;
public short MajorVersion;
public short MinorVersion;
public long FileReferenceNumber;
public long ParentFileReferenceNumber;
public long Usn;
public long TimeStamp;
public int Reason;
public int SourceInfo;
public int SecurityId;
public FileAttributes FileAttributes;
public short FileNameLength;
public short FileNameOffset;
}
[StructLayout(LayoutKind.Sequential)]
private struct IO_STATUS_BLOCK
{
public int Status;
public int Information;
}
[StructLayout(LayoutKind.Sequential)]
private struct UNICODE_STRING
{
public short Length;
public short MaximumLength;
public IntPtr Buffer;
}
[StructLayout(LayoutKind.Sequential)]
private struct OBJECT_ATTRIBUTES
{
public int Length;
public IntPtr RootDirectory;
public IntPtr ObjectName;
public int Attributes;
public int SecurityDescriptor;
public int SecurityQualityOfService;
}
//// MFT_ENUM_DATA
[DllImport("kernel32.dll", ExactSpelling = true, SetLastError = true, CharSet = CharSet.Auto)]
private static extern bool DeviceIoControl(IntPtr hDevice, int dwIoControlCode, ref MFT_ENUM_DATA lpInBuffer, int nInBufferSize, IntPtr lpOutBuffer, int nOutBufferSize, ref int lpBytesReturned, IntPtr lpOverlapped);
[DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Auto)]
private static extern IntPtr CreateFile(string lpFileName, uint dwDesiredAccess, int dwShareMode, IntPtr lpSecurityAttributes, int dwCreationDisposition, int dwFlagsAndAttributes, IntPtr hTemplateFile);
[DllImport("kernel32.dll", ExactSpelling = true, SetLastError = true, CharSet = CharSet.Auto)]
private static extern Int32 CloseHandle(IntPtr lpObject);
[DllImport("ntdll.dll", ExactSpelling = true, SetLastError = true, CharSet = CharSet.Auto)]
private static extern int NtCreateFile(ref IntPtr FileHandle, int DesiredAccess, ref OBJECT_ATTRIBUTES ObjectAttributes, ref IO_STATUS_BLOCK IoStatusBlock, int AllocationSize, int FileAttribs, int SharedAccess, int CreationDisposition, int CreateOptions, int EaBuffer,
int EaLength);
[DllImport("ntdll.dll", ExactSpelling = true, SetLastError = true, CharSet = CharSet.Auto)]
private static extern int NtQueryInformationFile(IntPtr FileHandle, ref IO_STATUS_BLOCK IoStatusBlock, IntPtr FileInformation, int Length, int FileInformationClass);
private IntPtr m_hCJ;
private IntPtr m_Buffer;
private int m_BufferSize;
private string m_DriveLetter;
private class FSNode
{
public long FRN;
public long ParentFRN;
public string FileName;
public bool IsFile;
public FSNode(long lFRN, long lParentFSN, string sFileName, bool bIsFile)
{
FRN = lFRN;
ParentFRN = lParentFSN;
FileName = sFileName;
IsFile = bIsFile;
}
}
private IntPtr OpenVolume(string szDriveLetter)
{
IntPtr hCJ = default(IntPtr);
//// volume handle
m_DriveLetter = szDriveLetter;
hCJ = CreateFile(@"\\.\" + szDriveLetter, GENERIC_READ, FILE_SHARE_READ | FILE_SHARE_WRITE, IntPtr.Zero, OPEN_EXISTING, 0, IntPtr.Zero);
return hCJ;
}
private void Cleanup()
{
if (m_hCJ != IntPtr.Zero)
{
// Close the volume handle.
CloseHandle(m_hCJ);
m_hCJ = INVALID_HANDLE_VALUE;
}
if (m_Buffer != IntPtr.Zero)
{
// Free the allocated memory
Marshal.FreeHGlobal(m_Buffer);
m_Buffer = IntPtr.Zero;
}
}
public IEnumerable EnumerateFiles(string szDriveLetter)
{
try
{
var usnRecord = default(USN_RECORD);
var mft = default(MFT_ENUM_DATA);
var dwRetBytes = 0;
var cb = 0;
var dicFRNLookup = new Dictionary();
var bIsFile = false;
// This shouldn't be called more than once.
if (m_Buffer.ToInt32() != 0)
{
throw new Exception("invalid buffer");
}
// Assign buffer size
m_BufferSize = 65536;
//64KB
// Allocate a buffer to use for reading records.
m_Buffer = Marshal.AllocHGlobal(m_BufferSize);
// correct path
szDriveLetter = szDriveLetter.TrimEnd('\\');
// Open the volume handle
m_hCJ = OpenVolume(szDriveLetter);
// Check if the volume handle is valid.
if (m_hCJ == INVALID_HANDLE_VALUE)
{
string errorMsg = "Couldn't open handle to the volume.";
if (!IsAdministrator())
errorMsg += "Current user is not administrator";
throw new Exception(errorMsg);
}
mft.StartFileReferenceNumber = 0;
mft.LowUsn = 0;
mft.HighUsn = long.MaxValue;
do
{
if (DeviceIoControl(m_hCJ, FSCTL_ENUM_USN_DATA, ref mft, Marshal.SizeOf(mft), m_Buffer, m_BufferSize, ref dwRetBytes, IntPtr.Zero))
{
cb = dwRetBytes;
// Pointer to the first record
IntPtr pUsnRecord = new IntPtr(m_Buffer.ToInt32() + 8);
while ((dwRetBytes > 8))
{
// Copy pointer to USN_RECORD structure.
usnRecord = (USN_RECORD)Marshal.PtrToStructure(pUsnRecord, usnRecord.GetType());
// The filename within the USN_RECORD.
string FileName = Marshal.PtrToStringUni(new IntPtr(pUsnRecord.ToInt32() + usnRecord.FileNameOffset), usnRecord.FileNameLength / 2);
bIsFile = !usnRecord.FileAttributes.HasFlag(FileAttributes.Directory);
dicFRNLookup.Add(usnRecord.FileReferenceNumber, new FSNode(usnRecord.FileReferenceNumber, usnRecord.ParentFileReferenceNumber, FileName, bIsFile));
// Pointer to the next record in the buffer.
pUsnRecord = new IntPtr(pUsnRecord.ToInt32() + usnRecord.RecordLength);
dwRetBytes -= usnRecord.RecordLength;
}
// The first 8 bytes is always the start of the next USN.
mft.StartFileReferenceNumber = Marshal.ReadInt64(m_Buffer, 0);
}
else
{
break; // TODO: might not be correct. Was : Exit Do
}
} while (!(cb <= 8));
// Resolve all paths for Files
foreach (FSNode oFSNode in dicFRNLookup.Values.Where(o => o.IsFile))
{
string sFullPath = oFSNode.FileName;
FSNode oParentFSNode = oFSNode;
while (dicFRNLookup.TryGetValue(oParentFSNode.ParentFRN, out oParentFSNode))
{
sFullPath = string.Concat(oParentFSNode.FileName, @"\", sFullPath);
}
sFullPath = string.Concat(szDriveLetter, @"\", sFullPath);
yield return sFullPath;
}
}
finally
{
//// cleanup
Cleanup();
}
}
public static bool IsAdministrator()
{
WindowsIdentity identity = WindowsIdentity.GetCurrent();
WindowsPrincipal principal = new WindowsPrincipal(identity);
return principal.IsInRole(WindowsBuiltInRole.Administrator);
}
} 本文还提供了一个扩展方法，方便我们获取某个磁盘下的所有的文件名。
public static class DriveInfoExtension
{
public static IEnumerable EnumerateFiles(this DriveInfo drive)
{
return (new MFTScanner()).EnumerateFiles(drive.Name);
}
} 需要注意的是，读取USN Journal是需要管理员权限的，因此使用这个类需要管理员权限才能正常运行。
另外，这个类封装的也略为简单，只读取了文件名，实际上还可以读取文件大小，属性等常用信息，修改一下代码非常容易获取这些属性。通过它们可以非常方便写出一些分析磁盘空间占用的程序，这里就不举例了。
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本文题目：如何用C#代码实现快速查询文件
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