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Annotation of researchv10no/sys/io/dsort.c, revision 1.1

1.1     ! root        1: /*
        !             2:  * Seek sort for disks.
        !             3:  *
        !             4:  * actf and actl are the ends of an ordered list of buffers
        !             5:  * bp is a new buffer, to be inserted in the list in a good place
        !             6:  * the buffers are ordered by `cylinder' which is expected in b_resid.
        !             7:  *
        !             8:  * the list is two ascending lists: those greater than the head end
        !             9:  * (the block being read or written now), and those less.
        !            10:  * the idea is to sweep across the disk slowly doing io, then
        !            11:  * seek quickly back and sweep again
        !            12:  */
        !            13: #include "sys/param.h"
        !            14: #include "sys/buf.h"
        !            15: 
        !            16: #define        b_cylin b_resid
        !            17: 
        !            18: disksort(actf, actl, bp)
        !            19: register struct buf **actf, **actl, *bp;
        !            20: {
        !            21:        register struct buf *ap;
        !            22:        register long cyl;
        !            23: 
        !            24:        if((ap = *actf) == NULL) {
        !            25:                *actf = *actl = bp;
        !            26:                bp->av_forw = NULL;
        !            27:                return;
        !            28:        }
        !            29:        if(bp->b_cylin < ap->b_cylin) {
        !            30:                while(ap->av_forw) {
        !            31:                        if(ap->av_forw->b_cylin < ap->b_cylin) {
        !            32:                                cyl = 0;
        !            33:                                break;
        !            34:                        }
        !            35:                        ap = ap->av_forw;
        !            36:                }
        !            37:        }
        !            38:        else
        !            39:                cyl = ap->b_cylin;
        !            40:        while(ap->av_forw) {
        !            41:                if(ap->av_forw->b_cylin < cyl ||
        !            42:                   bp->b_cylin < ap->av_forw->b_cylin)
        !            43:                        break;
        !            44:                ap = ap->av_forw;
        !            45:                cyl = ap->b_cylin;
        !            46:        }
        !            47:        bp->av_forw = ap->av_forw;
        !            48:        ap->av_forw = bp;
        !            49:        if(ap == *actl)
        !            50:                *actl = bp;
        !            51: }

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