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POWriting raw data to a disk in windows fails with error code 83 (invalid parameter)
 

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  1. POWriting raw data to a disk in windows fails with error code 83 (invalid parameter)
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    <p>I have a little snippet of code that I am trying to use to write a string that is roughly 100 bytes long to a disk at the address 0x600.</p> <pre><code>UCHAR szStr[0x4C] = {0}; memcpy(szStr, "Example string", 8); DWORD bytes, cb; HANDLE hDisk = CreateFile("\\\\.\\I:", GENERIC_WRITE | GENERIC_READ, FILE_SHARE_READ | FILE_SHARE_WRITE, NULL, OPEN_EXISTING, 0, NULL); if (hDisk == INVALID_HANDLE_VALUE) { cout &lt;&lt; "CreateFile error"&lt;&lt; endl &lt;&lt; GetLastError(); } if (!DeviceIoControl(hDisk, FSCTL_LOCK_VOLUME, NULL, 0, NULL, 0, &amp;cb, NULL)) { cout &lt;&lt; "IO Error"&lt;&lt; endl &lt;&lt; GetLastError(); } if (SetFilePointer(hDisk, 0x600, NULL, FILE_BEGIN) == INVALID_SET_FILE_POINTER) { cout &lt;&lt; "Pointer error"&lt;&lt; endl &lt;&lt; GetLastError(); } if (!WriteFile(hDisk, szStr, 0x4C, &amp;bytes, 0)) { cout &lt;&lt; "Write error" &lt;&lt; endl &lt;&lt; GetLastError(); //Only one that triggers (err code 87) } CloseHandle(hDisk); </code></pre> <p>For some reason everything is OK until I call <code>WriteFile()</code> which fails. <code>GetLastError()</code> returns a code of 83 which means <code>INVALID_PARAMETER</code>. I have tried debugging it by specifing a normal file on the desktop instead of the drive <code>I:\</code> and the operation fires off successfully so my best guess would be the problem lies with the disk handle to the drive <code>I:\</code>.</p> <p>I read an article by MSDN located <a href="http://msdn.microsoft.com/en-us/library/ff551353.aspx" rel="nofollow">here</a> that explains that raw disk I/O gets blocked if you don't lock/dismount the drive first. I am confused as to why that would be a problem as in my code I call <code>DeviceIoControl</code> with <code>FSCTL_LOCK_VOLUME</code> to lock the device before I perform anything else. The disk has an active file system (FAT32/FAT16) and the 0x600 region likely lies within the filesystem, but according to the article if I lock the drive I should be able to write to it. Any idea what is going on here? Thanks!</p>
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    1. COThe snippet you posted can never provide an error code, you are talking about code that we can't see. You don't check if the locking was successful. And for all we know, you might be calling GetLastError even if WriteFile didn't return FALSE. And you do pass invalid arguments, the length is incorrect.
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    2. CO@HansPassant I updated my code with the error checking like you said. Is checking the return code of `DeviceIoControl` enough to check if locking was successful? Also, what is the correct length, would it be 0x4C? Thanks.
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