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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 18:00 
GeneralPossible crash causess PinmemberSimon Owen25-Jun-06 22:58 
Could the crash on some systems be because you're passing a pointer in LPARAM, and it'll only be valid in your own address space? It'll only crash if something is registered for those notifications and tries to use the pointer. There's some extra magic involved when the system sends them, to ensure it's valid for whatever is receiving it.

Another possibility is that you're POSTING the messages, but the pointer you're passing is to a stack variable that will be out of scope before some applications have processed the message. Making the structure variable static would help, but only if the pointer is actually valid to other processes anyway.
Questionquery Pinmemberachalshah717-Mar-06 2:52 
GeneralSHChangeNotify PinmemberCabbi9-Jun-05 3:53 
Generalcan't refresh CDRW content PinsussSergey Apollonov23-May-05 20:34 
GeneralCode Correction : Drive Letter PinmemberBlake Miller12-Apr-05 5:30 
GeneralRe: Code Correction : Drive Letter Pinmembershaman7412-Apr-05 6:17 
GeneralHhhhhhhhhhhhhhh ! PinmemberKochise8-Apr-05 0:24 
GeneralRe: Hhhhhhhhhhhhhhh ! Pinmembershaman748-Apr-05 0:32 
GeneralRe: Hhhhhhhhhhhhhhh ! PinmemberOutlook14-Apr-05 11:41 
GeneralRe: Hhhhhhhhhhhhhhh ! Pinmembershaman7414-Apr-05 21:52 
GeneralRe: Hhhhhhhhhhhhhhh ! PinmemberMX-Mauro18-Apr-05 2:20 
GeneralRe: Hhhhhhhhhhhhhhh ! PinmemberAndy N18-Apr-05 14:15 

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