rdsprocess.c

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/* rdsprocess.c - rdsprocess */

#include <xinu.h>

/*------------------------------------------------------------------------
 * rdsprocess  -  High-priority background process that repeatedly
 *        extracts an item from the request queue, sends the
 *        request to the remote disk server, and handles the
 *        response, including caching responses blocks
 *------------------------------------------------------------------------
 */
void    rdsprocess (
      struct rdscblk    *rdptr  /* Ptr to device control block  */
    )
{
    struct  rd_msg_wreq msg;    /* Message to be sent       */
                    /*   (includes data area)   */
    struct  rd_msg_rres resp;   /* Buffer to hold response  */
                    /*   (includes data area)   */
    int32   retval;         /* Return value from rdscomm    */
    char    *idto;          /* Ptr to ID string copy    */
    char    *idfrom;        /* Ptr into ID string       */
    struct  rdbuff  *bptr;      /* Ptr to buffer at the head of */
                    /*   the request queue      */
    struct  rdbuff  *nptr;      /* Ptr to next buffer on the    */
                    /*   request queue      */
    struct  rdbuff  *pptr;      /* Ptr to previous buffer   */
    struct  rdbuff  *qptr;      /* Ptr that runs along the  */
                    /*   request queue      */
    int32   i;          /* Loop index           */

    while (TRUE) {          /* Do forever */

        /* Wait until the request queue contains a node */
        wait(rdptr->rd_reqsem);
        bptr = rdptr->rd_rhnext;

        /* Use operation in request to determine action */

       switch (bptr->rd_op) {

       case RD_OP_READ:

        /* Build a read request message for the server */

        msg.rd_type = htons(RD_MSG_RREQ);   /* Read request */
        msg.rd_status = htons(0);
        msg.rd_seq = 0;     /* Rdscomm fills in an entry    */
        idto = msg.rd_id;
        memset(idto, NULLCH, RD_IDLEN);/* Initialize ID to zero */
        idfrom = rdptr->rd_id;
        while ( (*idto++ = *idfrom++) != NULLCH ) { /* Copy ID  */
            ;
        }

        /* Send the message and receive a response */

        retval = rdscomm((struct rd_msg_hdr *)&msg,
                    sizeof(struct rd_msg_rreq),
                 (struct rd_msg_hdr *)&resp,
                    sizeof(struct rd_msg_rres),
                  rdptr );

        /* Check response */

        if ( (retval == SYSERR) || (retval == TIMEOUT) ||
                (ntohs(resp.rd_status) != 0) ) {
            panic("Failed to contact remote disk server");
        }

        /* Copy data from the reply into the buffer */

        for (i=0; i<RD_BLKSIZ; i++) {
            bptr->rd_block[i] = resp.rd_data[i];
        }

        /* Unlink buffer from the request queue */

        nptr = bptr->rd_next;
        pptr = bptr->rd_prev;
        nptr->rd_prev = bptr->rd_prev;
        pptr->rd_next = bptr->rd_next;

        /* Insert buffer in the cache */

        pptr = (struct rdbuff *) &rdptr->rd_chnext;
        nptr = pptr->rd_next;
        bptr->rd_next = nptr;
        bptr->rd_prev = pptr;
        pptr->rd_next = bptr;
        nptr->rd_prev = bptr;

        /* Initialize reference count */

        bptr->rd_refcnt = 1;

        /* Signal the available semaphore */

        signal(rdptr->rd_availsem);

        /* Send a message to waiting process */

        send(bptr->rd_pid, (uint32)bptr);

        /* If other processes are waiting to read the  */
        /*   block, notify them and remove the request */

        qptr = rdptr->rd_rhnext;
        while (qptr != (struct rdbuff *)&rdptr->rd_rtnext) {
            if (qptr->rd_blknum == bptr->rd_blknum) {
                bptr->rd_refcnt++;
                send(qptr->rd_pid,(uint32)bptr);

                /* Unlink request from queue    */

                pptr = qptr->rd_prev;
                nptr = qptr->rd_next;
                pptr->rd_next = bptr->rd_next;
                nptr->rd_prev = bptr->rd_prev;

                /* Move buffer to the free list */

                qptr->rd_next = rdptr->rd_free;
                rdptr->rd_free = qptr;
                signal(rdptr->rd_availsem);
                break;
            }
            qptr = qptr->rd_next;
        }
        break;

        case RD_OP_WRITE:

        /* Build a write request message for the server */

        msg.rd_type = htons(RD_MSG_WREQ);   /* Write request*/
        msg.rd_blk = bptr->rd_blknum;
        msg.rd_status = htons(0);
        msg.rd_seq = 0;     /* Rdscomb fills in an entry    */
        idto = msg.rd_id;
        memset(idto, NULLCH, RD_IDLEN);/* Initialize ID to zero */
        idfrom = rdptr->rd_id;
        while ( (*idto++ = *idfrom++) != NULLCH ) { /* Copy ID  */
            ;
        }
        for (i=0; i<RD_BLKSIZ; i++) {
            msg.rd_data[i] = bptr->rd_block[i];
        }

        /* Unlink buffer from request queue */

        nptr = bptr->rd_next;
        pptr = bptr->rd_prev;
        pptr->rd_next = nptr;
        nptr->rd_prev = pptr;

        /* Insert buffer in the cache */

        pptr = (struct rdbuff *) &rdptr->rd_chnext;
        nptr = pptr->rd_next;
        bptr->rd_next = nptr;
        bptr->rd_prev = pptr;
        pptr->rd_next = bptr;
        nptr->rd_prev = bptr;

        /* Declare that buffer is eligible for reuse */

        bptr->rd_refcnt = 0;
        signal(rdptr->rd_availsem);

        /* Send the message and receive a response */

        retval = rdscomm((struct rd_msg_hdr *)&msg,
                    sizeof(struct rd_msg_wreq),
                 (struct rd_msg_hdr *)&resp,
                    sizeof(struct rd_msg_wres),
                  rdptr );

        /* Check response */

        if ( (retval == SYSERR) || (retval == TIMEOUT) ||
                (ntohs(resp.rd_status) != 0) ) {
            panic("failed to contact remote disk server");
        }
        break;

        case RD_OP_SYNC:

        /* Send a message to the waiting process */

        send(bptr->rd_pid, OK);

        /* Unlink buffer from the request queue */

        nptr = bptr->rd_next;
        pptr = bptr->rd_prev;
        nptr->rd_prev = bptr->rd_prev;
        pptr->rd_next = bptr->rd_next;

        /* Insert buffer into the free list */

        bptr->rd_next = rdptr->rd_free;
        rdptr->rd_free = bptr;
        signal(rdptr->rd_availsem);
        break;
       }
    }
}