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POReadFile Kernel32 Maximum Buffer Size
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copied!<p>I am reading directly from a disk using C# and pinvoking the kernel32 ReadFile method. I notice that with larger reads (currently only reading in single chunks) the buffer size is out of range.</p> <p>Does anyone know the maximum size of the read buffer here? </p> <p>If so what is the purpose of limiting the buffer size when I have surplus memory I <em>want</em> to read into? I understand the concepts of buffering and keeping a small memory footprint but why is a small size forced upon us? Perhaps just an artefact of an old Win32 API?</p> <p>EDIT: The error received from <code>Marshal.GetLastWin32Error()</code> is "Value does not fall within the expected range."</p> <p>The upper limit before I receive this error is 8192 bytes (8KB - hence my confusion).</p> <pre><code>using System; using System.IO; using System.Runtime.InteropServices; using Microsoft.Win32.SafeHandles; namespace DiskRead { class Program { public const uint GenericRead = 0x80000000; public const uint FileShareRead = 1; public const uint FileShareWrite = 2; public const uint OpenExisting = 3; [DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Unicode)] private static extern IntPtr CreateFile(string lpFileName, uint dwDesiredAccess, uint dwShareMode, IntPtr lpSecurityAttributes, uint dwCreationDisposition, uint dwFlagsAndAttributes, IntPtr hTemplateFile); [DllImport("kernel32.dll", SetLastError = true)] static extern bool ReadFile(IntPtr hFile, [Out] byte[] lpBuffer, uint nNumberOfBytesToRead, out uint lpNumberOfBytesRead, IntPtr lpOverlapped); static void Main(string[] args) { string path = @"\\.\PhysicalDrive0"; IntPtr ptr = CreateFile(path, GenericRead, FileShareRead | FileShareWrite, IntPtr.Zero, OpenExisting, 0, IntPtr.Zero); SafeFileHandle handleValue = new SafeFileHandle(ptr, true); FileStream fileStream = new FileStream(handleValue, FileAccess.Read); const uint numberOfBytesToRead = 8193; uint bytesRead; byte[] buffer = new byte[numberOfBytesToRead]; if (!ReadFile(handleValue.DangerousGetHandle(), buffer, numberOfBytesToRead, out bytesRead, IntPtr.Zero)) { Marshal.ThrowExceptionForHR(Marshal.GetHRForLastWin32Error()); } } } } </code></pre> <p>Thanks in advance.</p>

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