projects / unix-history / blame
| Commit | Line | Data |
|---|---|---|
| cd1b1cd4 | 1 | /* ufs_disksubr.c 4.3 81/03/09 */ |
| 200a8f27 BJ |
2 | |
| 3 | /* | |
| 0d67fde4 BJ |
4 | * Seek sort for disks. We depend on the driver |
| 5 | * which calls us using b_resid as the current cylinder number. | |
| 6 | * | |
| 7 | * The argument dp structure holds a b_actf activity chain pointer | |
| 8 | * on which we keep two queues, sorted in ascending cylinder order. | |
| 9 | * The first queue holds those requests which are positioned after | |
| 10 | * the current cylinder (in the first request); the second holds | |
| 11 | * requests which came in after their cylinder number was passed. | |
| 12 | * Thus we implement a one way scan, retracting after reaching the | |
| 13 | * end of the drive to the first request on the second queue, | |
| 14 | * at which time it becomes the first queue. | |
| 15 | * | |
| 16 | * A one-way scan is natural because of the way UNIX read-ahead | |
| 17 | * blocks are allocated. | |
| 200a8f27 BJ |
18 | */ |
| 19 | ||
| 20 | #include "../h/param.h" | |
| 21 | #include "../h/systm.h" | |
| 22 | #include "../h/buf.h" | |
| 23 | ||
| 24 | #define b_cylin b_resid | |
| 25 | ||
| 26 | disksort(dp, bp) | |
| 0d67fde4 | 27 | register struct buf *dp, *bp; |
| 200a8f27 BJ |
28 | { |
| 29 | register struct buf *ap; | |
| 200a8f27 | 30 | |
| 0d67fde4 BJ |
31 | /* |
| 32 | * If nothing on the activity queue, then | |
| 33 | * we become the only thing. | |
| 34 | */ | |
| 200a8f27 BJ |
35 | ap = dp->b_actf; |
| 36 | if(ap == NULL) { | |
| 37 | dp->b_actf = bp; | |
| 38 | dp->b_actl = bp; | |
| 39 | bp->av_forw = NULL; | |
| 40 | return; | |
| 41 | } | |
| 0d67fde4 BJ |
42 | /* |
| 43 | * If we lie after the first (currently active) | |
| 44 | * request, then we must locate the second request list | |
| 45 | * and add ourselves to it. | |
| 46 | */ | |
| 47 | if (bp->b_cylin < ap->b_cylin) { | |
| 48 | while (ap->av_forw) { | |
| 49 | /* | |
| 50 | * Check for an ``inversion'' in the | |
| 51 | * normally ascending cylinder numbers, | |
| 52 | * indicating the start of the second request list. | |
| 53 | */ | |
| 54 | if (ap->av_forw->b_cylin < ap->b_cylin) { | |
| 55 | /* | |
| 56 | * Search the second request list | |
| 57 | * for the first request at a larger | |
| 58 | * cylinder number. We go before that; | |
| 59 | * if there is no such request, we go at end. | |
| 60 | */ | |
| 61 | do { | |
| 62 | if (bp->b_cylin < ap->av_forw->b_cylin) | |
| 63 | goto insert; | |
| 64 | ap = ap->av_forw; | |
| 65 | } while (ap->av_forw); | |
| 66 | goto insert; /* after last */ | |
| 67 | } | |
| 68 | ap = ap->av_forw; | |
| 200a8f27 | 69 | } |
| 0d67fde4 BJ |
70 | /* |
| 71 | * No inversions... we will go after the last, and | |
| 72 | * be the first request in the second request list. | |
| 73 | */ | |
| 74 | goto insert; | |
| 200a8f27 | 75 | } |
| 0d67fde4 BJ |
76 | /* |
| 77 | * Request is at/after the current request... | |
| 78 | * sort in the first request list. | |
| 79 | */ | |
| 80 | while (ap->av_forw) { | |
| 81 | /* | |
| 82 | * We want to go after the current request | |
| 83 | * if there is an inversion after it (i.e. it is | |
| 84 | * the end of the first request list), or if | |
| 85 | * the next request is a larger cylinder than our request. | |
| 86 | */ | |
| 87 | if (ap->av_forw->b_cylin < ap->b_cylin || | |
| 88 | bp->b_cylin < ap->av_forw->b_cylin) | |
| 89 | goto insert; | |
| 90 | ap = ap->av_forw; | |
| 91 | } | |
| 92 | /* | |
| 93 | * Neither a second list nor a larger | |
| 94 | * request... we go at the end of the first list, | |
| 95 | * which is the same as the end of the whole schebang. | |
| 96 | */ | |
| 97 | insert: | |
| 98 | bp->av_forw = ap->av_forw; | |
| 99 | ap->av_forw = bp; | |
| 100 | if (ap == dp->b_actl) | |
| 200a8f27 BJ |
101 | dp->b_actl = bp; |
| 102 | } |