getbuf.c

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#include <xinu.h>

char *getbuf(bpid32 poolid)
{
    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;
}