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Annotation of 43BSDReno/lib/libc/gen/telldir.c, revision 1.1.1.1

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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