/* getbuf.c - getbuf */

#include 

/*------------------------------------------------------------------------
 *  getbuf  -  Get a buffer from a preestablished buffer pool
 *------------------------------------------------------------------------
 */
char    *getbuf(
          bpid32        poolid          /* Index of pool in buftab      */
        )
{
        intmask mask;                   /* Saved interrupt mask         */
        struct  bpentry *bpptr;         /* Pointer to entry in buftab   */
        struct  bpentry *bufptr;        /* Pointer to a buffer          */

        mask = disable();

        /* Check arguments */

        if ( (poolid < 0  ||  poolid >= nbpools) ) {
                restore(mask);
                return (char *)SYSERR;

        }
        bpptr = &buftab[poolid];

        /* Wait for pool to have > 0 buffers and allocate a buffer */

        wait(bpptr->bpsem);
        bufptr = bpptr->bpnext;

        /* Unlink buffer from pool */

        bpptr->bpnext = bufptr->bpnext;

        /* Record pool ID in first four bytes of buffer and skip */

        *(bpid32 *)bufptr = poolid;
        bufptr = (struct bpentry *)(sizeof(bpid32) + (char *)bufptr);
        restore(mask);
        return (char *)bufptr;
}