How can i remove a USB flash disk programmatically using delphi?

Question

How can I detect and remove a USB flash disk programatically using delphi?

I have seen some of the examples in this website, but they lack clear explanation on how t

Answer 1

This doesn't eject the drive, but it flushes the drive buffers and makes it safe to remove. It requires administrative rights under Vista and higher (and XP if running as a limited rights user, IIRC). It probably should have a try..finally to make sure that CloseHandle gets called; I leave that as an exercise to the reader, since code formattig is tight here without horizontal scrolling. :-)

unit USBDriveFlush;

interface

  uses Windows;

type
  // Taken from JEDI JwaWinIoctl
  PSTORAGE_HOTPLUG_INFO = ^STORAGE_HOTPLUG_INFO;
  {$EXTERNALSYM PSTORAGE_HOTPLUG_INFO}
  _STORAGE_HOTPLUG_INFO = record
    Size: DWORD; // version
    MediaRemovable: BOOLEAN; // ie. zip, jaz, cdrom, mo, etc. vs hdd
    MediaHotplug: BOOLEAN;   // ie. does the device succeed a lock 
                             // even though its not lockable media?
    DeviceHotplug: BOOLEAN;  // ie. 1394, USB, etc.
    WriteCacheEnableOverride: BOOLEAN; // This field should not be 
                             // relied upon because it is no longer used
  end;
  {$EXTERNALSYM _STORAGE_HOTPLUG_INFO}
  STORAGE_HOTPLUG_INFO = _STORAGE_HOTPLUG_INFO;
  {$EXTERNALSYM STORAGE_HOTPLUG_INFO}
  TStorageHotplugInfo = STORAGE_HOTPLUG_INFO;
  PStorageHotplugInfo = PSTORAGE_HOTPLUG_INFO;    

  function FlushUSBDrive(const Drive: string): Boolean;

implementation

function FlushUSBDrive(const Drive: string): Boolean;
var
  shpi : TStorageHotplugInfo;
  retlen : DWORD; //unneeded, but deviceiocontrol expects it
  h : THandle;
begin
  Result := False;
  h := CreateFile(PChar('\\.\' + Drive),
                  0,
                  FILE_SHARE_READ or FILE_SHARE_WRITE,
                  nil,
                  OPEN_EXISTING,
                  0,
                  0);
  if h <> INVALID_HANDLE_VALUE then
  begin
    shpi.Size := SizeOf(shpi);

    if DeviceIoControl(h,
                       IOCTL_STORAGE_GET_HOTPLUG_INFO,
                       nil,
                       0,
                       @shpi,
                       SizeOf(shpi),
                       retlen,
                       nil) then
    begin
      //shpi now has the existing values, so you can check to
      //see if the device is already hot-pluggable
      if not shpi.DeviceHotplug then
      begin
        shpi.DeviceHotplug:= True;

        //Need to use correct administrator security privilages here
        //otherwise it'll just give 'access is denied' error
        Result := DeviceIoControl(h,
                                  IOCTL_STORAGE_SET_HOTPLUG_INFO,
                                   @shpi,
                                   SizeOf(shpi),
                                   nil,
                                   0,
                                   retlen,
                                   nil);
      end;
    end;
    CloseHandle(h);
  end;
end;

Sample use:

if FlushUSBDrive('G:') then
  ShowMessage('Safe to remove USB drive G:')
else
  ShowMessage('Flush of drive G: failed!' +
    SysErrorMessage(GetLastError()));