如何在 NTFS 上创建稀疏文件？答案

【问题标题】：How to create a sparse file on NTFS?如何在 NTFS 上创建稀疏文件？
【发布时间】：2011-04-30 00:24:59
【问题描述】：

我正在测试一个稀疏文件。但是我的测试代码运行不好。

HANDLE h = CreateFileW(L"D:\\sparse.test",
        GENERIC_READ|GENERIC_WRITE,
        FILE_SHARE_READ|FILE_SHARE_WRITE|FILE_SHARE_DELETE,
        0,
        CREATE_ALWAYS,
        FILE_ATTRIBUTE_ARCHIVE|FILE_ATTRIBUTE_SPARSE_FILE,
        0);

DWORD d = GetFileAttributes(L"D:\\sparse.test");
// The function returns 32(FILE_ATTRIBUTE_ARCHIVE).
// Where is FILE_ATTRIBUTE_SPARSE_FILE flag?
// How do I make a sparse file.

DWORD written;
WriteFile(h, "aaa", 3, &written, 0);
SetFilePointer(h, 2*1024*1024*1023, 0, FILE_BEGIN);
SetEndOfFile(h);
WriteFile(h, "bbb", 3, &written, 0);

【问题讨论】：

标签： windows winapi file-io ntfs sparse-file

【解决方案1】：

您必须创建一个普通文件，然后使用DeviceIoControl 和FSCTL_SET_SPARSE 使其成为稀疏文件。

【讨论】：

@Benjamin：我不知道另一种方法可以完成这项工作。
需要指出的是，所有写入文件的数据总是物理分配的，即使只是0-bytes。因此，根据用例，可能需要额外使用 FSCTL_SET_ZERO_DATA: When you perform a write operation (with a function or operation other than FSCTL_SET_ZERO_DATA) whose data consists of nothing but zeros, zeros will be written to the disk for the entire length of the write. To zero out a range of the file and maintain sparseness, use FSCTL_SET_ZERO_DATA. docs.microsoft.com/de-de/windows/desktop/FileIO/…
微软自己的文档在其他地方另有说明：When a write operation is attempted where a large amount of the data in the buffer is zeros, the zeros are not written to the file.docs.microsoft.com/en-us/windows/desktop/fileio/sparse-files 也许不同之处在于措辞，所有0 与只有一些，两种情况下的行为不同？不过，对我来说没有多大意义。

【解决方案2】：

#include <windows.h>
#include <string>
#include <iostream>

HANDLE CreateSparseFile(LPCTSTR lpSparseFileName)
{
    // Use CreateFile as you would normally - Create file with whatever flags 
    //and File Share attributes that works for you
    DWORD dwTemp;

    HANDLE hSparseFile = CreateFile(lpSparseFileName,
        GENERIC_READ | GENERIC_WRITE,
        FILE_SHARE_READ | FILE_SHARE_WRITE,
        NULL,
        CREATE_ALWAYS,
        FILE_ATTRIBUTE_NORMAL,
        NULL);

    if (hSparseFile == INVALID_HANDLE_VALUE)
        return hSparseFile;

    DeviceIoControl(hSparseFile,
        FSCTL_SET_SPARSE,
        NULL,
        0,
        NULL,
        0,
        &dwTemp,
        NULL);
    return hSparseFile;
}

DWORD SetSparseRange(HANDLE hSparseFile, LONGLONG start, LONGLONG size)
{
    // Specify the starting and the ending address (not the size) of the 
    // sparse zero block
    FILE_ZERO_DATA_INFORMATION fzdi;
    fzdi.FileOffset.QuadPart = start;
    fzdi.BeyondFinalZero.QuadPart = start + size;
    // Mark the range as sparse zero block
    DWORD dwTemp;
    SetLastError(0);
    BOOL bStatus = DeviceIoControl(hSparseFile,
        FSCTL_SET_ZERO_DATA,
        &fzdi,
        sizeof(fzdi),
        NULL,
        0,
        &dwTemp,
        NULL);
    if (bStatus) return 0; //Sucess
    else {
        DWORD e = GetLastError();
        return(e); //return the error value
    }
}
int _tmain(int argc, _TCHAR* argv[])
{
    if (argc < 3) {
        std::cerr << "USAGE: SparseFile filename size" << std::endl;
        return 1;
    }

    try {
        ULONGLONG size = std::stoull(argv[2]);
        HANDLE h = CreateSparseFile(argv[1]);
        if (h == INVALID_HANDLE_VALUE) {
            std::cerr << "Unable to create file" << std::endl;
            return 1;
        }
        if (SetSparseRange(h, 0, size) != 0) {
            std::cerr << "Unable to set sparse range" << std::endl;
            return 1;
        }
        LARGE_INTEGER seek;
        seek.QuadPart = size;
        if (!SetFilePointerEx(h, seek, 0, 0)) {
            std::cerr << "Unable to seek to desired offset" << std::endl;
            return 1;
        }
        SetEndOfFile(h);
        CloseHandle(h);
    } catch (const std::exception &ex) {
        std::cerr << ex.what() << std::endl;
    }

    return 0;
}

【讨论】：

这是否为 2010 年的答案添加了任何新内容？
@ThomasWeller 这是一个使用相同想法的完整工作示例。
@ThomasWeller 它引起了FSCTL_SET_ZERO_DATA 的注意，因此我认为这是更好的答案。如果要写入更大的0-bytes 块，则需要这样做，否则将在物理上分配，因此应牢记。 docs.microsoft.com/de-de/windows/desktop/FileIO/…