使用CopyFile将一个小文件从一个盘拷贝到另一个盘，这个文件是立刻被写入磁盘还是先存在缓冲区里？

Question

使用WriteFile写文件的时候这些数据实际上是先存在OS的缓存里，要想立刻存入磁盘需要调用FlushFileBuffers。那么使用CopyFile拷贝文件会怎样？

Answer 1

那在调用完CopyFile后有相关Flush的函数吗，没有找到~~

Answer 2

可能直接就写盘了。
据说windows2000 以后，不但会写盘，
还要把目标数据同原始数据比对一次，无误,系统才算完成copy.

Answer 3

CopyFile提供了回调函数，每传输 64KB 数据回调一次。
底层具体是怎么一步步操作的就不清楚了

Answer 4

先放缓冲才写盘, CopyFile是CreateFile+ReadFile+WriteFile+CloseFile

Answer 5

这个是在MSDN上看到的吗？如果是这样最好了。

Answer 6

这样的话它并没有调用flush函数，那也就是copy完了并一定就真的写到硬盘上了。

Answer 7

CloseHandle的时候, 就都写了. CopyFile结束,肯定是全部写完成的. 如不用CloseHandle, 那就不一定了.

Answer 8

所以CreateFile写文件之后,一定要CloseHandle,或者你显示的调用Flush函数, 但这个Flush函数频烦调用, 严重影响性能. 
如果文件没有写完, 那么写完的数据大小应该是512的倍数(理论上是这样, 感兴趣的可以验证下,我也没验证)  

Answer 9

WriteFile 和 CopyFile 的功能和机制大不同
WriteFile 函数只是简单调用NtWriteFile 和ZwWriteFile ，所以他们有使用FlushFileBuffers的必要
而CopyFile 要复杂的多，则不需要，看看它们都调用了那些函数，就明白了    WriteFile 调用情况
    kernel32!WriteFile     
 kernel32!_SEH_epilog   
 kernel32!_SEH_prolog   
 ntdll!KiFastSystemCall 
 ntdll!NtWriteFile      
 ntdll!ZwWriteFile      
  CopyFile 调用情况
 kernel32!BaseCopyStream                         
kernel32!BaseIsThisAConsoleName                 
kernel32!Basep8BitStringToDynamicUnicodeString  
kernel32!Basep8BitStringToStaticUnicodeString   
kernel32!BasepCopyEncryption                    
kernel32!BasepCopyFileExW                       
kernel32!BasepProcessNameGrafting               
kernel32!CloseHandle                            
kernel32!CopyFileA                              
kernel32!CopyFileExW                            
kernel32!CreateFileW                            
kernel32!SetLastError                           
kernel32!WriteFile                              
kernel32!_SEH_epilog                            
kernel32!_SEH_prolog                            
kernel32!__security_check_cookie                
ntdll!KiFastSystemCall                          
ntdll!NtClose                                   
ntdll!NtCreateFile                              
ntdll!NtCreateSection                           
ntdll!NtMapViewOfSection                        
ntdll!NtQueryInformationFile                    
ntdll!NtSetInformationFile                      
ntdll!NtUnmapViewOfSection                      
ntdll!NtWriteFile                               
ntdll!RtlAcquirePebLock                         
ntdll!RtlAllocateHeap                           
ntdll!RtlAllocateHeapSlowly                     
ntdll!RtlAnsiStringToUnicodeString              
ntdll!RtlCompareMemory                          
ntdll!RtlCompareMemoryUlong                     
ntdll!RtlDebugAllocateHeap                      
ntdll!RtlDebugFreeHeap                          
ntdll!RtlDetermineDosPathNameType_U             
ntdll!RtlDosPathNameToNtPathName_U              
ntdll!RtlDosPathNameToNtPathName_Ustr           
ntdll!RtlEnterCriticalSection                   
ntdll!RtlEqualUnicodeString                     
ntdll!RtlFillMemoryUlong                        
ntdll!RtlFreeAnsiString                         
ntdll!RtlFreeHeap                               
ntdll!RtlFreeHeapSlowly                         
ntdll!RtlGetFullPathName_Ustr                   
ntdll!RtlGetNtGlobalFlags                       
ntdll!RtlInitAnsiString                         
ntdll!RtlInitString                             
ntdll!RtlInitUnicodeString                      
ntdll!RtlInitUnicodeStringEx                    
ntdll!RtlIsDosDeviceName_U                      
ntdll!RtlIsDosDeviceName_Ustr                   
ntdll!RtlLeaveCriticalSection                   
ntdll!RtlMultiByteToUnicodeN                    
ntdll!RtlMultiByteToUnicodeSize                 
ntdll!RtlReleasePebLock                         
ntdll!RtlUpcaseUnicodeChar                      
ntdll!RtlpCheckBusyBlockTail                    
ntdll!RtlpCheckHeapSignature                    
ntdll!RtlpCoalesce reeBlocks                   
ntdll!RtlpGetExtraStuffPointer                  
ntdll!RtlpSysVolAllocate                        
ntdll!RtlpSysVolFree                            
ntdll!RtlpUpdateIndexInsertBlock                
ntdll!RtlpUpdateIndexRemoveBlock                
ntdll!RtlpValidateCurrentDirectory              
ntdll!RtlpValidateHeap                          
ntdll!RtlpValidateHeapEntry                     
ntdll!RtlpValidateHeapHeaders                   
ntdll!RtlxAnsiStringToUnicodeSize               
ntdll!ZwClose                                   
ntdll!ZwCreateSection                           
ntdll!ZwMapViewOfSection                        
ntdll!ZwQueryInformationFile                    
ntdll!ZwQueryVolumeInformationFile              
ntdll!ZwSetInformationFile                      
ntdll!ZwUnmapViewOfSection                      
ntdll!ZwWriteFile                               
ntdll!_SEH_epilog                               
ntdll!_SEH_prolog                               
ntdll!__security_check_cookie                   
ntdll!memmove                                   
ntdll!wcslen                                    

Answer 10

WriteFile也不需要FlushFileBuffers, 最后关闭句柄就完事了. 只有在不想关文件句柄又想写完当前文件数据的情况才需要这个. 
CopyFile就是对CreateFile,WriteFile...这些函数的封装,要进行准备和扫尾工作, 当然用到的函数多了. 

Answer 11

Ring3层对文件的操作最终都转到调用NtCreateFile系列函数

Answer 12

windbg一下可以得到。
从copyfile信息看它是做了安全检查，速度优化等方面的处理，里面有MapViewOfSection 等函数。