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Annotation of 43BSDTahoe/sys/tahoe/ufs_machdep.c, revision 1.1

1.1     ! root        1: /*
        !             2:  * Copyright (c) 1983, 1988 Regents of the University of California.
        !             3:  * All rights reserved.
        !             4:  *
        !             5:  * Redistribution and use in source and binary forms are permitted
        !             6:  * provided that the above copyright notice and this paragraph are
        !             7:  * duplicated in all such forms and that any documentation,
        !             8:  * advertising materials, and other materials related to such
        !             9:  * distribution and use acknowledge that the software was developed
        !            10:  * by the University of California, Berkeley.  The name of the
        !            11:  * University may not be used to endorse or promote products derived
        !            12:  * from this software without specific prior written permission.
        !            13:  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
        !            14:  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
        !            15:  * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
        !            16:  *
        !            17:  *     @(#)ufs_machdep.c       7.2 (Berkeley) 6/29/88
        !            18:  */
        !            19: 
        !            20: #include "param.h"
        !            21: #include "systm.h"
        !            22: #include "dir.h"
        !            23: #include "user.h"
        !            24: #include "buf.h"
        !            25: #include "conf.h"
        !            26: #include "proc.h"
        !            27: #include "seg.h"
        !            28: #include "vm.h"
        !            29: 
        !            30: #include "pte.h"
        !            31: 
        !            32: /*
        !            33:  * Machine dependent handling of the buffer cache.
        !            34:  */
        !            35: 
        !            36: /*
        !            37:  * Expand or contract the actual memory allocated to a buffer.
        !            38:  * If no memory is available, release buffer and take error exit
        !            39:  */
        !            40: allocbuf(tp, size)
        !            41:        register struct buf *tp;
        !            42:        int size;
        !            43: {
        !            44:        register struct buf *bp, *ep;
        !            45:        int sizealloc, take;
        !            46: 
        !            47:        sizealloc = roundup(size, CLBYTES);
        !            48:        /*
        !            49:         * Buffer size does not change
        !            50:         */
        !            51:        if (sizealloc == tp->b_bufsize)
        !            52:                goto out;
        !            53:        /*
        !            54:         * Buffer size is shrinking.
        !            55:         * Place excess space in a buffer header taken from the
        !            56:         * BQ_EMPTY buffer list and placed on the "most free" list.
        !            57:         * If no extra buffer headers are available, leave the
        !            58:         * extra space in the present buffer.
        !            59:         */
        !            60:        if (sizealloc < tp->b_bufsize) {
        !            61:                ep = bfreelist[BQ_EMPTY].av_forw;
        !            62:                if (ep == &bfreelist[BQ_EMPTY])
        !            63:                        goto out;
        !            64:                notavail(ep);
        !            65:                pagemove(tp->b_un.b_addr + sizealloc, ep->b_un.b_addr,
        !            66:                    (int)tp->b_bufsize - sizealloc);
        !            67:                ep->b_bufsize = tp->b_bufsize - sizealloc;
        !            68:                tp->b_bufsize = sizealloc;
        !            69:                ep->b_flags |= B_INVAL;
        !            70:                ep->b_bcount = 0;
        !            71:                brelse(ep);
        !            72:                goto out;
        !            73:        }
        !            74:        /*
        !            75:         * More buffer space is needed. Get it out of buffers on
        !            76:         * the "most free" list, placing the empty headers on the
        !            77:         * BQ_EMPTY buffer header list.
        !            78:         */
        !            79:        while (tp->b_bufsize < sizealloc) {
        !            80:                take = sizealloc - tp->b_bufsize;
        !            81:                bp = getnewbuf();
        !            82:                if (take >= bp->b_bufsize)
        !            83:                        take = bp->b_bufsize;
        !            84:                pagemove(&bp->b_un.b_addr[bp->b_bufsize - take],
        !            85:                    &tp->b_un.b_addr[tp->b_bufsize], take);
        !            86:                tp->b_bufsize += take;
        !            87:                bp->b_bufsize = bp->b_bufsize - take;
        !            88:                if (bp->b_bcount > bp->b_bufsize)
        !            89:                        bp->b_bcount = bp->b_bufsize;
        !            90:                if (bp->b_bufsize <= 0) {
        !            91:                        bremhash(bp);
        !            92:                        binshash(bp, &bfreelist[BQ_EMPTY]);
        !            93:                        bp->b_dev = (dev_t)NODEV;
        !            94:                        bp->b_error = 0;
        !            95:                        bp->b_flags |= B_INVAL;
        !            96:                }
        !            97:                brelse(bp);
        !            98:        }
        !            99: out:
        !           100:        tp->b_bcount = size;
        !           101:        return (1);
        !           102: }
        !           103: 
        !           104: /*
        !           105:  * Release space associated with a buffer.
        !           106:  */
        !           107: bfree(bp)
        !           108:        struct buf *bp;
        !           109: {
        !           110: 
        !           111:        bp->b_bcount = 0;
        !           112: }

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