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Annotation of 43BSDReno/lib/libc/gen/telldir.c, revision 1.1

1.1     ! root        1: /*
        !             2:  * Copyright (c) 1983 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: (1) source distributions retain this entire copyright
        !             7:  * notice and comment, and (2) distributions including binaries display
        !             8:  * the following acknowledgement:  ``This product includes software
        !             9:  * developed by the University of California, Berkeley and its contributors''
        !            10:  * in the documentation or other materials provided with the distribution
        !            11:  * and in all advertising materials mentioning features or use of this
        !            12:  * software. Neither the name of the University nor the names of its
        !            13:  * contributors may be used to endorse or promote products derived
        !            14:  * from this software without specific prior written permission.
        !            15:  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
        !            16:  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
        !            17:  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
        !            18:  */
        !            19: 
        !            20: #if defined(LIBC_SCCS) && !defined(lint)
        !            21: static char sccsid[] = "@(#)telldir.c  5.8 (Berkeley) 6/1/90";
        !            22: #endif /* LIBC_SCCS and not lint */
        !            23: 
        !            24: #include <sys/param.h>
        !            25: #include <dirent.h>
        !            26: 
        !            27: /*
        !            28:  * The option SINGLEUSE may be defined to say that a telldir
        !            29:  * cookie may be used only once before it is freed. This option
        !            30:  * is used to avoid having memory usage grow without bound.
        !            31:  */
        !            32: #define SINGLEUSE
        !            33: 
        !            34: /*
        !            35:  * One of these structures is malloced to describe the current directory
        !            36:  * position each time telldir is called. It records the current magic 
        !            37:  * cookie returned by getdirentries and the offset within the buffer
        !            38:  * associated with that return value.
        !            39:  */
        !            40: struct ddloc {
        !            41:        struct  ddloc *loc_next;/* next structure in list */
        !            42:        long    loc_index;      /* key associated with structure */
        !            43:        long    loc_seek;       /* magic cookie returned by getdirentries */
        !            44:        long    loc_loc;        /* offset of entry in buffer */
        !            45: };
        !            46: 
        !            47: #define        NDIRHASH        32      /* Num of hash lists, must be a power of 2 */
        !            48: #define        LOCHASH(i)      ((i)&(NDIRHASH-1))
        !            49: 
        !            50: static long    dd_loccnt;      /* Index of entry for sequential readdir's */
        !            51: static struct  ddloc *dd_hash[NDIRHASH];   /* Hash list heads for ddlocs */
        !            52: 
        !            53: /*
        !            54:  * return a pointer into a directory
        !            55:  */
        !            56: long
        !            57: telldir(dirp)
        !            58:        DIR *dirp;
        !            59: {
        !            60:        register int index;
        !            61:        register struct ddloc *lp;
        !            62: 
        !            63:        if ((lp = (struct ddloc *)malloc(sizeof(struct ddloc))) == NULL)
        !            64:                return (-1);
        !            65:        index = dd_loccnt++;
        !            66:        lp->loc_index = index;
        !            67:        lp->loc_seek = dirp->dd_seek;
        !            68:        lp->loc_loc = dirp->dd_loc;
        !            69:        lp->loc_next = dd_hash[LOCHASH(index)];
        !            70:        dd_hash[LOCHASH(index)] = lp;
        !            71:        return (index);
        !            72: }
        !            73: 
        !            74: /*
        !            75:  * seek to an entry in a directory.
        !            76:  * Only values returned by "telldir" should be passed to seekdir.
        !            77:  */
        !            78: void
        !            79: _seekdir(dirp, loc)
        !            80:        register DIR *dirp;
        !            81:        long loc;
        !            82: {
        !            83:        register struct ddloc *lp;
        !            84:        register struct ddloc **prevlp;
        !            85:        struct dirent *dp;
        !            86:        extern long lseek();
        !            87: 
        !            88:        prevlp = &dd_hash[LOCHASH(loc)];
        !            89:        lp = *prevlp;
        !            90:        while (lp != NULL) {
        !            91:                if (lp->loc_index == loc)
        !            92:                        break;
        !            93:                prevlp = &lp->loc_next;
        !            94:                lp = lp->loc_next;
        !            95:        }
        !            96:        if (lp == NULL)
        !            97:                return;
        !            98:        if (lp->loc_loc == dirp->dd_loc && lp->loc_seek == dirp->dd_seek)
        !            99:                goto found;
        !           100:        (void) lseek(dirp->dd_fd, lp->loc_seek, 0);
        !           101:        dirp->dd_seek = lp->loc_seek;
        !           102:        dirp->dd_loc = 0;
        !           103:        while (dirp->dd_loc < lp->loc_loc) {
        !           104:                dp = readdir(dirp);
        !           105:                if (dp == NULL)
        !           106:                        break;
        !           107:        }
        !           108: found:
        !           109: #ifdef SINGLEUSE
        !           110:        *prevlp = lp->loc_next;
        !           111:        free((caddr_t)lp);
        !           112: #endif
        !           113: }

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