A stream handler must also support SpiInstallProtocol to be able to receive the SPCB's. For example, suppose an application or media driver wants to install another SPCB of the same data type and subtype as an SPCB that it already has installed. The application or media driver will need to assign a new internal key value, that is used to differentiate between multiple SPCB's of the same data stream type. All the default SPCBs are installed with an internal key value of 0. Any additional SPCBs that overlap any of the data types that are already installed, need to use a different internal key value. Therefore, the stream handler must have code that allows for this scenario.
The sample code in the following example illustrates how to install stream protocol.
RC ShcInstallProtocol(pipparm)
PPARM_INSTPROT pipparm;
{ /* Start of ShcInstallProtocol */
RC rc = NO_ERROR; /* local return code */
int notfound = TRUE;
PESPCB pTempEspcb;
PESPCB pPrevEspcb;
/* the ESPCB list is under semaphore control */
if (!(rc = DosRequestMutexSem(hmtxGlobalData, SEM_INDEFINITE_WAIT)))
{ /* obtained semaphore */
if (pipparm->ulFlag & SPI_DEINSTALL_PROTOCOL)
{ /* DeInstall */
/* To Deinstall, Find the spcb, */
/* Take it off the espcb chain, */
/* Free the espcb memory allocated */
rc = ERROR_INVALID_SPCBKEY;
pPrevEspcb = NULL;
pTempEspcb = pESPCB_ListHead;
while (pTempEspcb && notfound)
{ /* Loop thru espcbs */
if ((pipparm->spcbkey.ulDataType ==
pTempEspcb->spcb.spcbkey.ulDataType) &&
(pipparm->spcbkey.ulDataSubType ==
pTempEspcb->spcb.spcbkey.ulDataSubType) &&
(pipparm->spcbkey.ulIntKey ==
pTempEspcb->spcb.spcbkey.ulIntKey))
{ /* found match */
notfound = FALSE;
rc = NO_ERROR;
/* Take the espcb off the chain */
if (pPrevEspcb)
{
pPrevEspcb->pnxtESPCB = pTempEspcb->pnxtESPCB;
}
else
{
pESPCB_ListHead = pTempEspcb->pnxtESPCB;
}
HhpFreeMem(hHeap, pTempEspcb);
} /* found match */
else
{ /* try the next espcb in the chain */
pPrevEspcb = pTempEspcb;
pTempEspcb = pTempEspcb->pnxtESPCB;
} /* try the next espcb in the chain */
} /* Loop thru espcbs */
} /* DeInstall */
else
{ /* Install */
/* If the SPCB already exists then error */
if (ShFindEspcb(pipparm->spcbkey))
{
rc = ERROR_INVALID_SPCBKEY;
}
else
{ /* OK to add spcb */
/* Allocate the espcb and put it on the front of the chain */
pTempEspcb = (PESPCB)HhpAllocMem(hHeap, sizeof(ESPCB));
if (pTempEspcb)
{
pTempEspcb->spcb = *(pipparm->pspcb);
pTempEspcb->pnxtESPCB = pESPCB_ListHead;
pESPCB_ListHead = pTempEspcb;
}
else
}
rc = ERROR_ALLOC_RESOURCES;
}
} /* OK to add spcb */
} /* Install */
DosReleaseMutexSem(hmtxGlobalData);
} /* obtained semaphore */
return(rc);
} /* End of ShcInstallProtocol */
Note: For descriptions of the parameters in the SPCB, see Stream Handlers.