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Programmatic Refresh of a File System

, 17 Apr 2005
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How to force the file system to refresh.


This is a short article, written after many hours spent on the problem of refreshing a CD file system after burning. At the end, the solution I've found is very very simple, so I've decided to explain it here.

The function

I've used a call to the BroadcastSystemMessage function to send a WM_DEVICECHANGE message to Windows (XP in my case). The function is defined as follows (found on MSDN):

long BroadcastSystemMessage(      
    DWORD dwFlags,
    LPDWORD lpdwRecipients,
    UINT uiMessage,
    WPARAM wParam,
    LPARAM lParam

To set the correct parameters for the call, I've initialized a DEV_BROADCAST_VOLUME struct, which is defined as:

typedef struct _DEV_BROADCAST_VOLUME {
  DWORD dbcv_size;
  DWORD dbcv_devicetype;
  DWORD dbcv_reserved;
  DWORD dbcv_unitmask;
  WORD dbcv_flags;

The code of my function is here:

bool RefreshFileSystem(char cdrive)
  long result;

  hdr.dbcv_size       =  sizeof(DEV_BROADCAST_VOLUME);
  hdr.dbcv_devicetype =  DBT_DEVTYP_VOLUME;
  hdr.dbcv_reserved = 0;
  cdrive = (char)_totupper(cdrive));  // thanks to Blake Miller
  hdr.dbcv_unitmask = 1 << (cdrive-'A');
  hdr.dbcv_flags  = DBTF_MEDIA;

  result = BroadcastSystemMessage(BSF_NOHANG|BSF_POSTMESSAGE,
  return (result>=0);

I've heard of someone who used this kind of a solution but unfortunately the system crashed. I'm trying to find out what has caused the crash.


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Comments and Discussions

GeneralC# code - Works for me on network drives Pinmembertheit851412-Jun-11 17:00 
Had to find a way to refresh the user's my computer windows to show drive mapping updates...
Here is my C# code:
        /// <summary>
        /// Changed for C# and to allow for network drive types.
        /// </summary>
        /// <param name="localDrive"></param>
        public static void RefreshDrive(string localDrive)
            // collect and clean the passed LocalDrive param
            if (localDrive == null || localDrive.Length == 0)
                throw new System.Exception("Invalid 'localDrive' passed, 'localDrive' parameter cannot be 'empty'");
            char drive = localDrive[0];
            long result;
            hdr.dbcv_size = (uint)Marshal.SizeOf(hdr);
            hdr.dbcv_devicetype = (uint)DevType.DBT_DEVTYP_NET;
            hdr.dbcv_reserved = 0;
            hdr.dbcv_unitmask = (uint) 1 << (drive - 'A');
            hdr.dbcv_flags = (ushort)Dbtf.DBTF_NET;
            IntPtr hdrp = Marshal.AllocHGlobal(Marshal.SizeOf(hdr));
            Marshal.StructureToPtr(hdr, hdrp, true);
            MessageBroadcastRecipients recip = MessageBroadcastRecipients.BSM_ALLCOMPONENTS;
            result = BroadcastSystemMessage(MessageBroadcastFlags.BSF_NOHANG | MessageBroadcastFlags.BSF_POSTMESSAGE,
                                   ref recip, WM_DEVICECHANGE, (IntPtr)DBT_DEVICEARRIVAL, hdrp);
        [DllImport("user32", SetLastError = true)]
        private static extern int BroadcastSystemMessage(MessageBroadcastFlags flags, ref MessageBroadcastRecipients lpInfo, uint Msg, IntPtr wParam, IntPtr lParam);
        const uint WM_DEVICECHANGE = 0x0219;
        const uint DBT_DEVICEARRIVAL = 0x8000;
        enum DevType : uint
            DBT_DEVTYP_OEM = 0,
            DBT_DEVTYP_DEVNODE = 1,
            DBT_DEVTYP_VOLUME = 2,
            DBT_DEVTYP_PORT = 3,
            DBT_DEVTYP_NET = 4,
        enum Dbtf : uint
            DBTF_MEDIA = 0x0001,
            DBTF_NET = 0x0002,
        enum MessageBroadcastFlags : uint
            BSF_QUERY = 0x00000001,
            BSF_IGNORECURRENTTASK = 0x00000002,
            BSF_FLUSHDISK = 0x00000004,
            BSF_NOHANG = 0x00000008,
            BSF_POSTMESSAGE = 0x00000010,
            BSF_FORCEIFHUNG = 0x00000020,
            BSF_NOTIMEOUTIFNOTHUNG = 0x00000040,
            BSF_ALLOWSFW = 0x00000080,
            BSF_SENDNOTIFYMESSAGE = 0x00000100,
            BSF_RETURNHDESK = 0x00000200,
            BSF_LUID = 0x00000400
        enum MessageBroadcastRecipients : uint
            BSM_ALLCOMPONENTS = 0x00000000,
            BSM_VXDS = 0x00000001,
            BSM_NETDRIVER = 0x00000002,
            BSM_INSTALLABLEDRIVERS = 0x00000004,
            BSM_APPLICATIONS = 0x00000008,
            BSM_ALLDESKTOPS = 0x00000010
        public struct DEV_BROADCAST_VOLUME
            public uint dbcv_size;
            public uint dbcv_devicetype;
            public uint dbcv_reserved;
            public uint dbcv_unitmask;
            public ushort dbcv_flags;
If you're unmapping a drive and remapping it to a different location, you must call RefreshDrive after the unmap and then after the mapping. If you do just one, the drive map may disappear or still show the old name.
            // Unmap the existing drive, if it exists.
            MapDrive(Drive, uncpath);

GeneralPossible crash causess PinmemberSimon Owen25-Jun-06 21:58 
Questionquery Pinmemberachalshah717-Mar-06 1:52 
GeneralSHChangeNotify PinmemberCabbi9-Jun-05 2:53 
Generalcan't refresh CDRW content PinsussSergey Apollonov23-May-05 19:34 
GeneralCode Correction : Drive Letter PinmemberBlake Miller12-Apr-05 4:30 
GeneralRe: Code Correction : Drive Letter Pinmembershaman7412-Apr-05 5:17 
GeneralHhhhhhhhhhhhhhh ! PinmemberKochise7-Apr-05 23:24 
GeneralRe: Hhhhhhhhhhhhhhh ! Pinmembershaman747-Apr-05 23:32 
GeneralRe: Hhhhhhhhhhhhhhh ! PinmemberOutlook14-Apr-05 10:41 
GeneralRe: Hhhhhhhhhhhhhhh ! Pinmembershaman7414-Apr-05 20:52 
GeneralRe: Hhhhhhhhhhhhhhh ! PinmemberMX-Mauro18-Apr-05 1:20 
GeneralRe: Hhhhhhhhhhhhhhh ! PinmemberAndy N18-Apr-05 13:15 

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