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Annotation of 42BSD/sys/vax/ufs_machdep.c, revision 1.1

1.1     ! root        1: /*     ufs_machdep.c   6.1     83/07/29        */
        !             2: 
        !             3: #include "../machine/pte.h"
        !             4: 
        !             5: #include "../h/param.h"
        !             6: #include "../h/systm.h"
        !             7: #include "../h/dir.h"
        !             8: #include "../h/user.h"
        !             9: #include "../h/buf.h"
        !            10: #include "../h/conf.h"
        !            11: #include "../h/proc.h"
        !            12: #include "../h/seg.h"
        !            13: #include "../h/vm.h"
        !            14: 
        !            15: /*
        !            16:  * Machine dependent handling of the buffer cache.
        !            17:  */
        !            18: 
        !            19: /*
        !            20:  * Expand or contract the actual memory allocated to a buffer.
        !            21:  * If no memory is available, release buffer and take error exit
        !            22:  */
        !            23: allocbuf(tp, size)
        !            24:        register struct buf *tp;
        !            25:        int size;
        !            26: {
        !            27:        register struct buf *bp, *ep;
        !            28:        int sizealloc, take;
        !            29: 
        !            30:        sizealloc = roundup(size, CLBYTES);
        !            31:        /*
        !            32:         * Buffer size does not change
        !            33:         */
        !            34:        if (sizealloc == tp->b_bufsize)
        !            35:                goto out;
        !            36:        /*
        !            37:         * Buffer size is shrinking.
        !            38:         * Place excess space in a buffer header taken from the
        !            39:         * BQ_EMPTY buffer list and placed on the "most free" list.
        !            40:         * If no extra buffer headers are available, leave the
        !            41:         * extra space in the present buffer.
        !            42:         */
        !            43:        if (sizealloc < tp->b_bufsize) {
        !            44:                ep = bfreelist[BQ_EMPTY].av_forw;
        !            45:                if (ep == &bfreelist[BQ_EMPTY])
        !            46:                        goto out;
        !            47:                notavail(ep);
        !            48:                pagemove(tp->b_un.b_addr + sizealloc, ep->b_un.b_addr,
        !            49:                    (int)tp->b_bufsize - sizealloc);
        !            50:                ep->b_bufsize = tp->b_bufsize - sizealloc;
        !            51:                tp->b_bufsize = sizealloc;
        !            52:                ep->b_flags |= B_INVAL;
        !            53:                ep->b_bcount = 0;
        !            54:                brelse(ep);
        !            55:                goto out;
        !            56:        }
        !            57:        /*
        !            58:         * More buffer space is needed. Get it out of buffers on
        !            59:         * the "most free" list, placing the empty headers on the
        !            60:         * BQ_EMPTY buffer header list.
        !            61:         */
        !            62:        while (tp->b_bufsize < sizealloc) {
        !            63:                take = sizealloc - tp->b_bufsize;
        !            64:                bp = getnewbuf();
        !            65:                if (take >= bp->b_bufsize)
        !            66:                        take = bp->b_bufsize;
        !            67:                pagemove(&bp->b_un.b_addr[bp->b_bufsize - take],
        !            68:                    &tp->b_un.b_addr[tp->b_bufsize], take);
        !            69:                tp->b_bufsize += take;
        !            70:                bp->b_bufsize = bp->b_bufsize - take;
        !            71:                if (bp->b_bcount > bp->b_bufsize)
        !            72:                        bp->b_bcount = bp->b_bufsize;
        !            73:                if (bp->b_bufsize <= 0) {
        !            74:                        bremhash(bp);
        !            75:                        binshash(bp, &bfreelist[BQ_EMPTY]);
        !            76:                        bp->b_dev = (dev_t)NODEV;
        !            77:                        bp->b_error = 0;
        !            78:                        bp->b_flags |= B_INVAL;
        !            79:                }
        !            80:                brelse(bp);
        !            81:        }
        !            82: out:
        !            83:        tp->b_bcount = size;
        !            84:        return (1);
        !            85: }
        !            86: 
        !            87: /*
        !            88:  * Release space associated with a buffer.
        !            89:  */
        !            90: bfree(bp)
        !            91:        struct buf *bp;
        !            92: {
        !            93: 
        !            94:        bp->b_bcount = 0;
        !            95: }

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