gen/telldir.c

   1 /*
   2  * Copyright (c) 1999 Apple Computer, Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * The contents of this file constitute Original Code as defined in and
   7  * are subject to the Apple Public Source License Version 1.1 (the
   8  * "License").  You may not use this file except in compliance with the
   9  * License.  Please obtain a copy of the License at
  10  * http://www.apple.com/publicsource and read it before using this file.
  11  *
  12  * This Original Code and all software distributed under the License are
  13  * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  14  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  15  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  16  * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
  17  * License for the specific language governing rights and limitations
  18  * under the License.
  19  *
  20  * @APPLE_LICENSE_HEADER_END@
  21  */
  22 /*
  23  * Copyright (c) 1983, 1993
  24  *      The Regents of the University of California.  All rights reserved.
  25  *
  26  * Redistribution and use in source and binary forms, with or without
  27  * modification, are permitted provided that the following conditions
  28  * are met:
  29  * 1. Redistributions of source code must retain the above copyright
  30  *    notice, this list of conditions and the following disclaimer.
  31  * 2. Redistributions in binary form must reproduce the above copyright
  32  *    notice, this list of conditions and the following disclaimer in the
  33  *    documentation and/or other materials provided with the distribution.
  34  * 3. All advertising materials mentioning features or use of this software
  35  *    must display the following acknowledgement:
  36  *      This product includes software developed by the University of
  37  *      California, Berkeley and its contributors.
  38  * 4. Neither the name of the University nor the names of its contributors
  39  *    may be used to endorse or promote products derived from this software
  40  *    without specific prior written permission.
  41  *
  42  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  43  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  44  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  45  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  46  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  47  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  48  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  49  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  50  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  51  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  52  * SUCH DAMAGE.
  53  */
  54
  55
  56 #include <sys/param.h>
  57 #include <dirent.h>
  58 #include <stdlib.h>
  59 #include <unistd.h>
  60
  61 /*
  62  * The option SINGLEUSE may be defined to say that a telldir
  63  * cookie may be used only once before it is freed. This option
  64  * is used to avoid having memory usage grow without bound.
  65  */
  66 #define SINGLEUSE
  67
  68 /*
  69  * One of these structures is malloced to describe the current directory
  70  * position each time telldir is called. It records the current magic
  71  * cookie returned by getdirentries and the offset within the buffer
  72  * associated with that return value.
  73  */
  74 struct ddloc {
  75         struct  ddloc *loc_next;/* next structure in list */
  76         long    loc_index;      /* key associated with structure */
  77         long    loc_seek;       /* magic cookie returned by getdirentries */
  78         long    loc_loc;        /* offset of entry in buffer */
  79 };
  80
  81 #define NDIRHASH        32      /* Num of hash lists, must be a power of 2 */
  82 #define LOCHASH(i)      ((i)&(NDIRHASH-1))
  83
  84 static long     dd_loccnt;      /* Index of entry for sequential readdir's */
  85 static struct   ddloc *dd_hash[NDIRHASH];   /* Hash list heads for ddlocs */
  86
  87 /*
  88  * return a pointer into a directory
  89  */
  90 long
  91 telldir(dirp)
  92         const DIR *dirp;
  93 {
  94         register int index;
  95         register struct ddloc *lp;
  96
  97         if ((lp = (struct ddloc *)malloc(sizeof(struct ddloc))) == NULL)
  98                 return (-1);
  99         index = dd_loccnt++;
 100         lp->loc_index = index;
 101         lp->loc_seek = dirp->dd_seek;
 102         lp->loc_loc = dirp->dd_loc;
 103         lp->loc_next = dd_hash[LOCHASH(index)];
 104         dd_hash[LOCHASH(index)] = lp;
 105         return (index);
 106 }
 107
 108 /*
 109  * seek to an entry in a directory.
 110  * Only values returned by "telldir" should be passed to seekdir.
 111  */
 112 void
 113 _seekdir(dirp, loc)
 114         register DIR *dirp;
 115         long loc;
 116 {
 117         register struct ddloc *lp;
 118         register struct ddloc **prevlp;
 119         struct dirent *dp;
 120
 121         prevlp = &dd_hash[LOCHASH(loc)];
 122         lp = *prevlp;
 123         while (lp != NULL) {
 124                 if (lp->loc_index == loc)
 125                         break;
 126                 prevlp = &lp->loc_next;
 127                 lp = lp->loc_next;
 128         }
 129         if (lp == NULL)
 130                 return;
 131         if (lp->loc_loc == dirp->dd_loc && lp->loc_seek == dirp->dd_seek)
 132                 goto found;
 133         (void) lseek(dirp->dd_fd, (off_t)lp->loc_seek, SEEK_SET);
 134         dirp->dd_seek = lp->loc_seek;
 135         dirp->dd_loc = 0;
 136         while (dirp->dd_loc < lp->loc_loc) {
 137                 dp = readdir(dirp);
 138                 if (dp == NULL)
 139                         break;
 140         }
 141 found:
 142 #ifdef SINGLEUSE
 143         *prevlp = lp->loc_next;
 144         free((caddr_t)lp);
 145 #endif
 146 }