c++ - WriteFile 失败超过 4700 个 block (SD 卡原始写入/窗口)

Question

我正在 SD 卡上写入/读取原始数据。编写代码的工作量约为。 4700 block 并在此限制后失败。这是代码:

   //Data to be written
   uint8_t* sessions;
   sessions = (uint8_t *) malloc(2048*sizeof(uint8_t));
   unsigned int i;
   for(i=0;i<(2048*sizeof(uint8_t));i++) sessions[i]=8;

   DWORD dwWrite;

   HANDLE hDisk=CreateFileA("\\\\.\\K:",  // drive to open = SD CARD
            GENERIC_WRITE,                // access to the drive
            FILE_SHARE_READ | // share mode
            FILE_SHARE_WRITE,
            NULL,             // default security attributes
            OPEN_EXISTING,    // disposition
            FILE_FLAG_NO_BUFFERING,               // file attributes
            NULL);            // do not copy file attributes


   if(hDisk==INVALID_HANDLE_VALUE) 
   {
      CloseHandle(hDisk);
      printf("ERROR opening the file !!! ");
   }

   DWORD dwPtr = SetFilePointer(hDisk,10000*512,0,FILE_BEGIN); //4700 OK 

   if (dwPtr == INVALID_SET_FILE_POINTER) // Test for failure
   {
     printf("CANNOT move the file pointer !!! ");
   }

   //Try using this structure but same results: CAN BE IGNORED
   OVERLAPPED osWrite      = {0,0,0};
   memset(&osWrite, 0, sizeof(osWrite));
   osWrite.Offset = 10000*512;                //4700 OK
   osWrite.hEvent = CreateEvent(FALSE, FALSE, FALSE, FALSE);

   if( FALSE ==  WriteFile(hDisk,sessions,2048,&dwWrite,&osWrite) ){
       printf("CANNOT write data to the SD card!!! %lu",dwWrite);
   }else{
       printf("Written %lu on SD card",dwWrite);
   }

   CloseHandle(hDisk);

问题出在函数“Writefile”(windows.h) 上。如果 block 数小于 4700。一切都很好(数据写入 SD 卡)但如果 block 数比方说 5000 或 10000，函数将失败“写入 0”。

请注意，如果没有 FILE_FLAG_NO_BUFFERING，则无法打开驱动器(SD 卡)。 “OVERLAPPED”是使其工作的失败尝试，不使用它 (WriteFile(hDisk,sessions,2048,&dwWrite,NULL) ) 会导致相同的行为。 “SetFilePointer”也适用于高于 4700 的 block 。还测试了 2 种不同的 SD 卡。我在 Windows 10 上。

关于发生了什么的任何提示？

感谢您的参与

Answer 1

来自documentation for WriteFile :

A write on a volume handle will succeed if the volume does not have a mounted file system, or if one of the following conditions is true:

• The sectors to be written to are boot sectors.

• The sectors to be written to reside outside of file system space.

• You have explicitly locked or dismounted the volume by using FSCTL_LOCK_VOLUME or FSCTL_DISMOUNT_VOLUME.

• The volume has no actual file system. (In other words, it has a RAW file system mounted.)

您可以写入前几兆字节，因为(出于历史原因)文件系统不使用该空间。为了写入卷的其余部分，您首先必须使用 FSCTL_LOCK_VOLUME control code 锁定卷。 .