gen/telldir.c

   1 /*
   2  * Copyright (c) 1999 Apple Computer, Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * Copyright (c) 1999-2003 Apple Computer, Inc.  All Rights Reserved.
   7  *
   8  * This file contains Original Code and/or Modifications of Original Code
   9  * as defined in and that are subject to the Apple Public Source License
  10  * Version 2.0 (the 'License'). You may not use this file except in
  11  * compliance with the License. Please obtain a copy of the License at
  12  * http://www.opensource.apple.com/apsl/ and read it before using this
  13  * file.
  14  *
  15  * The Original Code and all software distributed under the License are
  16  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  17  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  18  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  19  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  20  * Please see the License for the specific language governing rights and
  21  * limitations under the License.
  22  *
  23  * @APPLE_LICENSE_HEADER_END@
  24  */
  25 /*
  26  * Copyright (c) 1983, 1993
  27  *      The Regents of the University of California.  All rights reserved.
  28  *
  29  * Redistribution and use in source and binary forms, with or without
  30  * modification, are permitted provided that the following conditions
  31  * are met:
  32  * 1. Redistributions of source code must retain the above copyright
  33  *    notice, this list of conditions and the following disclaimer.
  34  * 2. Redistributions in binary form must reproduce the above copyright
  35  *    notice, this list of conditions and the following disclaimer in the
  36  *    documentation and/or other materials provided with the distribution.
  37  * 3. All advertising materials mentioning features or use of this software
  38  *    must display the following acknowledgement:
  39  *      This product includes software developed by the University of
  40  *      California, Berkeley and its contributors.
  41  * 4. Neither the name of the University nor the names of its contributors
  42  *    may be used to endorse or promote products derived from this software
  43  *    without specific prior written permission.
  44  *
  45  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  46  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  47  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  48  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  49  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  50  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  51  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  52  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  53  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  54  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  55  * SUCH DAMAGE.
  56  */
  57
  58
  59 #include <sys/param.h>
  60 #include <dirent.h>
  61 #include <stdlib.h>
  62 #include <unistd.h>
  63
  64 /*
  65  * The option SINGLEUSE may be defined to say that a telldir
  66  * cookie may be used only once before it is freed. This option
  67  * is used to avoid having memory usage grow without bound.
  68  */
  69 #define SINGLEUSE
  70
  71 /*
  72  * One of these structures is malloced to describe the current directory
  73  * position each time telldir is called. It records the current magic
  74  * cookie returned by getdirentries and the offset within the buffer
  75  * associated with that return value.
  76  */
  77 struct ddloc {
  78         struct  ddloc *loc_next;/* next structure in list */
  79         long    loc_index;      /* key associated with structure */
  80         long    loc_seek;       /* magic cookie returned by getdirentries */
  81         long    loc_loc;        /* offset of entry in buffer */
  82 };
  83
  84 #define NDIRHASH        32      /* Num of hash lists, must be a power of 2 */
  85 #define LOCHASH(i)      ((i)&(NDIRHASH-1))
  86
  87 static long     dd_loccnt;      /* Index of entry for sequential readdir's */
  88 static struct   ddloc *dd_hash[NDIRHASH];   /* Hash list heads for ddlocs */
  89
  90 /*
  91  * return a pointer into a directory
  92  */
  93 long
  94 telldir(dirp)
  95         const DIR *dirp;
  96 {
  97         register int index;
  98         register struct ddloc *lp;
  99
 100         if ((lp = (struct ddloc *)malloc(sizeof(struct ddloc))) == NULL)
 101                 return (-1);
 102         index = dd_loccnt++;
 103         lp->loc_index = index;
 104         lp->loc_seek = dirp->dd_seek;
 105         lp->loc_loc = dirp->dd_loc;
 106         lp->loc_next = dd_hash[LOCHASH(index)];
 107         dd_hash[LOCHASH(index)] = lp;
 108         return (index);
 109 }
 110
 111 /*
 112  * seek to an entry in a directory.
 113  * Only values returned by "telldir" should be passed to seekdir.
 114  */
 115 void
 116 _seekdir(dirp, loc)
 117         register DIR *dirp;
 118         long loc;
 119 {
 120         register struct ddloc *lp;
 121         register struct ddloc **prevlp;
 122         struct dirent *dp;
 123
 124         prevlp = &dd_hash[LOCHASH(loc)];
 125         lp = *prevlp;
 126         while (lp != NULL) {
 127                 if (lp->loc_index == loc)
 128                         break;
 129                 prevlp = &lp->loc_next;
 130                 lp = lp->loc_next;
 131         }
 132         if (lp == NULL)
 133                 return;
 134         if (lp->loc_loc == dirp->dd_loc && lp->loc_seek == dirp->dd_seek)
 135                 goto found;
 136         (void) lseek(dirp->dd_fd, (off_t)lp->loc_seek, SEEK_SET);
 137         dirp->dd_seek = lp->loc_seek;
 138         dirp->dd_loc = 0;
 139         while (dirp->dd_loc < lp->loc_loc) {
 140                 dp = readdir(dirp);
 141                 if (dp == NULL)
 142                         break;
 143         }
 144 found:
 145 #ifdef SINGLEUSE
 146         *prevlp = lp->loc_next;
 147         free((caddr_t)lp);
 148 #endif
 149 }