Read Sectors From a Disk

VixDiskLib_Read() reads a range of sectors from an open virtual disk. You specify the beginning sector and the number of sectors. Sector size could vary, but is defined in <vixDiskLib.h> as 512 bytes because VMDK files have that sector size.

vixError = VixDiskLib_Read(srcHandle, i, j, buf);

In vSphere 6.7 and later, you can improve performance of NBD transport with asynchronous reads. Asynchronous calls may be used for all transport modes, because they fall back to synchronous as needed.

// customized callback for complete notification
void myDiskLibCompletion(void *cbData, VixError result);
// a loop for multiple read requests
for (...)
   vixError = VixDiskLib_ReadAsync(srcHandle, i, j, buf, myDiskLibCompletion, cbData);
   if (vixError != VIX_ASYNC) {
      // handle error
   }
}
VixDiskLib_Wait(srcHandle); // wait ror all async read to complete