/* pipeputc.c - pipeputc */

#include 

/*------------------------------------------------------------------------
 *  pipeputc  -  write one character to a pipe device
 *------------------------------------------------------------------------
 */
devcall pipe_putc(
          struct dentry *devptr,        /* Entry in device switch table */
          char  ch                      /* Byte to write                */
        )
{
        struct  pipecblk *piptr;        /* Pointer to pipe control block*/

        /* Get a pointer to the control block for this pipe */

        piptr = &pipetab[devptr->dvminor];

        /* Check that the pipe is available for writing */

        if (piptr->pstate != PIPE_OPEN) {
                return SYSERR;
        }

        wait(piptr->ppsem);

        /* See if pipe was closed or set to EOF while we were blocked   */
        
        if (piptr->pstate != PIPE_OPEN) {
                return SYSERR;
        }

        /* Deposit a byte in next buffer position */

        piptr->pbuf[piptr->ptail++] = ch;
        if (piptr->ptail >= PIPE_BUF_SIZE) {
                piptr->ptail = 0;
        }
        piptr->pavail++;

        /* Signal the consumer semaphore and return */

        signal(piptr->pcsem);
        return OK;
}