.Net中的Junction Points怎么创建

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Junction Points是NTFS v5+的新特性，功能和我们所熟知的UNIX中的文件夹软链接类似（与windows中的文件夹快捷方式不同的是，它进行了路径重定向）。如在Vista中的C:\Documents and Settings 就是C:\Users的一个链接。然而，在Windows中并没有提供相关命令，只能编程通过api来实现。

创建Junction Point

// Creates a Junction Point at// C:\Foo\JunctionPoint that points to the directory C:\Bar.// Fails if there is already a file,// directory or Junction Point with the specified path.JunctionPoint.Create(@"C:\Foo\JunctionPoint", @"C:\Bar",false)// Creates a Junction Point at C:\Foo\JunctionPoint that points to// the directory C:\Bar.// Replaces an existing Junction Point if found at the specified path.JunctionPoint.Create(@"C:\Foo\JunctionPoint", @"C:\Bar", true)

注：不能对文件创建Junction Points.

删除Junction Point

// Delete a Junction Point at C:\Foo\JunctionPoint if it exists.// Does nothing if there is no such Junction Point.// Fails if the specified path refers to an existing file or// directory rather than a Junction Point.JunctionPoint.Delete(@"C:\Foo\JunctionPoint")

判断Junction Point是否存在

// Returns true if there is a Junction Point at C:\Foo\JunctionPoint.// Returns false if the specified path refers to an existing file// or directory rather than a Junction Point// or if it refers to the vacuum of space.bool exists = JunctionPoint.Exists(@"C:\Foo\JunctionPoint")

获取Junction Point所指向的实际地址

// Create a Junction Point for demonstration purposes whose target is C:\Bar.JunctionPoint.Create(@"C:\Foo\JunctionPoint", @"C:\Bar", false)// Returns the full path of the target of the Junction Point at// C:\Foo\JunctionPoint.// Fails if the specified path does not refer to a Junction Point.string target = JunctionPoint.GetTarget(@"C:\Foo\JunctionPoint")// target will be C:\Bar

注：这个函数有问题，对系统的权限要求过高，如果对系统盘的一些文件夹链接访问往往会报异常，我把它改了一下，新的代码如下：

    /// <summary>    /// Provides access to NTFS junction points in .Net.    /// </summary>    public static class JunctionPoint    {        /// <summary>        /// The file or directory is not a reparse point.        /// </summary>        private const int ERROR_NOT_A_REPARSE_POINT = 4390;        /// <summary>        /// The reparse point attribute cannot be set because it conflicts with an existing attribute.        /// </summary>        private const int ERROR_REPARSE_ATTRIBUTE_CONFLICT = 4391;        /// <summary>        /// The data present in the reparse point buffer is invalid.        /// </summary>        private const int ERROR_INVALID_REPARSE_DATA = 4392;        /// <summary>        /// The tag present in the reparse point buffer is invalid.        /// </summary>        private const int ERROR_REPARSE_TAG_INVALID = 4393;        /// <summary>        /// There is a mismatch between the tag specified in the request and the tag present in the reparse point.        /// </summary>        private const int ERROR_REPARSE_TAG_MISMATCH = 4394;        /// <summary>        /// Command to set the reparse point data block.        /// </summary>        private const int FSCTL_SET_REPARSE_POINT = 0x000900A4;        /// <summary>        /// Command to get the reparse point data block.        /// </summary>        private const int FSCTL_GET_REPARSE_POINT = 0x000900A8;        /// <summary>        /// Command to delete the reparse point data base.        /// </summary>        private const int FSCTL_DELETE_REPARSE_POINT = 0x000900AC;        /// <summary>        /// Reparse point tag used to identify mount points and junction points.        /// </summary>        private const uint IO_REPARSE_TAG_MOUNT_POINT = 0xA0000003;        /// <summary>        /// This prefix indicates to NTFS that the path is to be treated as a non-interpreted        /// path in the virtual file system.        /// </summary>        private const string NonInterpretedPathPrefix = @"\??\";        [Flags]        private enum EFileAccess : uint        {            GenericRead = 0x80000000,            GenericWrite = 0x40000000,            GenericExecute = 0x20000000,            GenericAll = 0x10000000,            GenericNone = 0x0,        }        [Flags]        private enum EFileShare : uint        {            None = 0x00000000,            Read = 0x00000001,            Write = 0x00000002,            Delete = 0x00000004,        }        private enum ECreationDisposition : uint        {            New = 1,            CreateAlways = 2,            OpenExisting = 3,            OpenAlways = 4,            TruncateExisting = 5,        }        [Flags]        private enum EFileAttributes : uint        {            Readonly = 0x00000001,            Hidden = 0x00000002,            System = 0x00000004,            Directory = 0x00000010,            ArcHive = 0x00000020,            Device = 0x00000040,            NORMal = 0x00000080,            Temporary = 0x00000100,            SparseFile = 0x00000200,            ReparsePoint = 0x00000400,            Compressed = 0x00000800,            Offline = 0x00001000,            NotContentIndexed = 0x00002000,            Encrypted = 0x00004000,            Write_Through = 0x80000000,            Overlapped = 0x40000000,            NoBuffering = 0x20000000,            RandoMaccess = 0x10000000,            SequentialScan = 0x08000000,            DeleteOnClose = 0x04000000,            BackupSemantics = 0x02000000,            PosixSemantics = 0x01000000,            OpenReparsePoint = 0x00200000,            OpenNoRecall = 0x00100000,            FirstPipeInstance = 0x00080000        }        [StructLayout(LayoutKind.Sequential)]        private struct REPARSE_DATA_BUFFER        {            /// <summary>            /// Reparse point tag. Must be a Microsoft reparse point tag.            /// </summary>            public uint ReparseTag;            /// <summary>            /// Size, in bytes, of the data after the Reserved member. This can be calculated by:            /// (4 * sizeof(ushort)) + SubstituteNameLength + PrintNameLength +             /// (namesAreNullTerminated ? 2 * sizeof(char) : 0);            /// </summary>            public ushort ReparseDataLength;            /// <summary>            /// Reserved; do not use.             /// </summary>            public ushort Reserved;            /// <summary>            /// Offset, in bytes, of the substitute name string in the PathBuffer array.            /// </summary>            public ushort SubstituteNameOffset;            /// <summary>            /// Length, in bytes, of the substitute name string. If this string is null-terminated,            /// SubstituteNameLength does not include space for the null character.            /// </summary>            public ushort SubstituteNameLength;            /// <summary>            /// Offset, in bytes, of the print name string in the PathBuffer array.            /// </summary>            public ushort PrintNameOffset;            /// <summary>            /// Length, in bytes, of the print name string. If this string is null-terminated,            /// PrintNameLength does not include space for the null character.             /// </summary>            public ushort PrintNameLength;            /// <summary>            /// A buffer containing the unicode-encoded path string. The path string contains            /// the substitute name string and print name string.            /// </summary>            [MarshalAs(UnmanagedType.ByValArray, SizeConst = 0x3FF0)]            public byte[] PathBuffer;        }        [DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]        private static extern bool Deviceiocontrol(IntPtr hDevice, uint dwIoControlCode,            IntPtr InBuffer, int nInBufferSize,            IntPtr OutBuffer, int nOutBufferSize,            out int pBytesReturned, IntPtr lpOverlapped);        [DllImport("kernel32.dll", SetLastError = true)]        private static extern IntPtr CreateFile(            string lpFileName,            EFileAccess dwDesiredAccess,            EFileShare dwShareMode,            IntPtr lpSecurityAttributes,            ECreationDisposition dwCreationDisposition,            EFileAttributes dwFlagsAndAttributes,            IntPtr hTemplateFile);        /// <summary>        /// Creates a junction point from the specified directory to the specified target directory.        /// </summary>        /// <remarks>        /// Only works on NTFS.        /// </remarks>        /// <param name="junctionPoint">The junction point path</param>        /// <param name="targetDir">The target directory</param>        /// <param name="overwrite">If true overwrites an existing reparse point or empty directory</param>        /// <exception cref="IOException">Thrown when the junction point could not be created or when        /// an existing directory was found and <paramref name="overwrite" /> if false</exception>        public static void Create(string junctionPoint, string targetDir, bool overwrite)        {            targetDir = Path.GetFullPath(targetDir);            if (!Directory.Exists(targetDir))                throw new IOException("Target path does not exist or is not a directory.");            if (Directory.Exists(junctionPoint))            {                if (!overwrite)                    throw new IOException("Directory already exists and overwrite parameter is false.");            }            else            {                Directory.CreateDirectory(junctionPoint);            }            using (SafeFileHandle handle = OpenReparsePoint(junctionPoint, EFileAccess.GenericWrite))            {                byte[] targetDirBytes = Encoding.Unicode.GetBytes(NonInterpretedPathPrefix + Path.GetFullPath(targetDir));                REPARSE_DATA_BUFFER reparseDataBuffer = new REPARSE_DATA_BUFFER();                reparseDataBuffer.ReparseTag = IO_REPARSE_TAG_MOUNT_POINT;                reparseDataBuffer.ReparseDataLength = (ushort)(targetDirBytes.Length + 12);                reparseDataBuffer.SubstituteNameOffset = 0;                reparseDataBuffer.SubstituteNameLength = (ushort)targetDirBytes.Length;                reparseDataBuffer.PrintNameOffset = (ushort)(targetDirBytes.Length + 2);                reparseDataBuffer.PrintNameLength = 0;                reparseDataBuffer.PathBuffer = new byte[0x3ff0];                Array.Copy(targetDirBytes, reparseDataBuffer.PathBuffer, targetDirBytes.Length);                int inBufferSize = Marshal.SizeOf(reparseDataBuffer);                IntPtr inBuffer = Marshal.AllocHGlobal(inBufferSize);                try                {                    Marshal.StructureToPtr(reparseDataBuffer, inBuffer, false);                    int bytesReturned;                    bool result = DeviceIoControl(handle.DangerousGetHandle(), FSCTL_SET_REPARSE_POINT,                        inBuffer, targetDirBytes.Length + 20, IntPtr.Zero, 0, out bytesReturned, IntPtr.Zero);                    if (!result)                        ThrowLastWin32Error("Unable to create junction point.");                }                finally                {                    Marshal.FreeHGlobal(inBuffer);                }            }        }        /// <summary>        /// Deletes a junction point at the specified source directory along with the directory itself.        /// Does nothing if the junction point does not exist.        /// </summary>        /// <remarks>        /// Only works on NTFS.        /// </remarks>        /// <param name="junctionPoint">The junction point path</param>        public static void Delete(string junctionPoint)        {            if (!Directory.Exists(junctionPoint))            {                if (File.Exists(junctionPoint))                    throw new IOException("Path is not a junction point.");                return;            }            using (SafeFileHandle handle = OpenReparsePoint(junctionPoint, EFileAccess.GenericWrite))            {                REPARSE_DATA_BUFFER reparseDataBuffer = new REPARSE_DATA_BUFFER();                reparseDataBuffer.ReparseTag = IO_REPARSE_TAG_MOUNT_POINT;                reparseDataBuffer.ReparseDataLength = 0;                reparseDataBuffer.PathBuffer = new byte[0x3ff0];                int inBufferSize = Marshal.SizeOf(reparseDataBuffer);                IntPtr inBuffer = Marshal.AllocHGlobal(inBufferSize);                try                {                    Marshal.StructureToPtr(reparseDataBuffer, inBuffer, false);                    int bytesReturned;                    bool result = DeviceIoControl(handle.DangerousGetHandle(), FSCTL_DELETE_REPARSE_POINT,                        inBuffer, 8, IntPtr.Zero, 0, out bytesReturned, IntPtr.Zero);                    if (!result)                        ThrowLastWin32Error("Unable to delete junction point.");                }                finally                {                    Marshal.FreeHGlobal(inBuffer);                }                try                {                    Directory.Delete(junctionPoint);                }                catch (IOException ex)                {                    throw new IOException("Unable to delete junction point.", ex);                }            }        }        /// <summary>        /// Determines whether the specified path exists and refers to a junction point.        /// </summary>        /// <param name="path">The junction point path</param>        /// <returns>True if the specified path represents a junction point</returns>        /// <exception cref="IOException">Thrown if the specified path is invalid        /// or some other error occurs</exception>        public static bool Exists(string path)        {            if (!Directory.Exists(path))                return false;            using (SafeFileHandle handle = OpenReparsePoint(path, EFileAccess.GenericRead))            {                string target = InternalGetTarget(handle);                return target != null;            }        }        /// <summary>        /// Gets the target of the specified junction point.        /// </summary>        /// <remarks>        /// Only works on NTFS.        /// </remarks>        /// <param name="junctionPoint">The junction point path</param>        /// <returns>The target of the junction point</returns>        /// <exception cref="IOException">Thrown when the specified path does not        /// exist, is invalid, is not a junction point, or some other error occurs</exception>        public static string GetTarget(string junctionPoint)        {            using (SafeFileHandle handle = OpenReparsePoint(junctionPoint, EFileAccess.GenericNone))            {                string target = InternalGetTarget(handle);                if (target == null)                    throw new IOException("Path is not a junction point.");                return target;            }        }        private static string InternalGetTarget(SafeFileHandle handle)        {            int outBufferSize = Marshal.SizeOf(typeof(REPARSE_DATA_BUFFER));            IntPtr outBuffer = Marshal.AllocHGlobal(outBufferSize);            try            {                int bytesReturned;                bool result = DeviceIoControl(handle.DangerousGetHandle(), FSCTL_GET_REPARSE_POINT,                    IntPtr.Zero, 0, outBuffer, outBufferSize, out bytesReturned, IntPtr.Zero);                if (!result)                {                    int error = Marshal.GetLastWin32Error();                    if (error == ERROR_NOT_A_REPARSE_POINT)                        return null;                    ThrowLastWin32Error("Unable to get information about junction point.");                }                REPARSE_DATA_BUFFER reparseDataBuffer = (REPARSE_DATA_BUFFER)                    Marshal.PtrToStructure(outBuffer, typeof(REPARSE_DATA_BUFFER));                if (reparseDataBuffer.ReparseTag != IO_REPARSE_TAG_MOUNT_POINT)                    return null;                string targetDir = Encoding.Unicode.GetString(reparseDataBuffer.PathBuffer,                    reparseDataBuffer.SubstituteNameOffset, reparseDataBuffer.SubstituteNameLength);                if (targetDir.StartsWith(NonInterpretedPathPrefix))                    targetDir = targetDir.Substring(NonInterpretedPathPrefix.Length);                return targetDir;            }            finally            {                Marshal.FreeHGlobal(outBuffer);            }        }        private static SafeFileHandle OpenReparsePoint(string reparsePoint, EFileAccess acceSSMode)        {            SafeFileHandle reparsePointHandle = new SafeFileHandle(CreateFile(reparsePoint, accessMode,                EFileShare.Read | EFileShare.Write | EFileShare.Delete,                IntPtr.Zero, ECreationDisposition.OpenExisting,                EFileAttributes.BackupSemantics | EFileAttributes.OpenReparsePoint, IntPtr.Zero), true);            if (Marshal.GetLastWin32Error() != 0)                ThrowLastWin32Error("Unable to open reparse point.");            return reparsePointHandle;        }        private static void ThrowLastWin32Error(string message)        {            throw new IOException(message, Marshal.GetExceptionForHR(Marshal.GetHRForLastWin32Error()));        }    }

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