Converting Applications Written for Pipes

Converting Applications Written for Pipes

Currently, an application written to use named pipes must perform basic Open, Close, Read, and Write processing on a pipe. With the VDI, these operations are performed with the following function calls:

• Read
  
  
• Write
  
  
• Flush
  
  
• ClearError

Initialization

For pipes, the WIN32 interfaces attempt to open and wait for the pipe interface to become available:

while(1) {
   h = CreateFile( <pipename>, OPEN_EXISTING...)
   if (h != INVALID_HANDLE_VALUE)
      break;  // continue with active phase
   WaitNamedPipe( <some interval of time>)
}

With the VDI, the client obtains a COM interface, creates the virtual device set, and then waits for the server to finish configuring it:

VDConfig config;
IClientVirtualDeviceSet2 *vds;
memset (&config, 0, sizeof(config));
config.deviceCount = 1;
CoCreateInstance(CLSID_MSSQL_ClientVirtualDeviceSet,
       NULL, CLSCTX_INPROC_SERVER, 
       IID_IClientVirtualDeviceSet2,
       &vds );
vds-> Create( <VDNAME>, &config)
vds-> GetConfiguration( &newConfig, timeout)

The invocation of the BACKUP or RESTORE command was not shown. The only difference in the command syntax is to specify VIRTUAL_DEVICE rather than pipe and the names of the devices themselves.