lib/libc/gen/telldir.c

   1 /*
   2  * Copyright (c) 1983, 1993
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 3. Neither the name of the University nor the names of its contributors
  14  *    may be used to endorse or promote products derived from this software
  15  *    without specific prior written permission.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  27  * SUCH DAMAGE.
  28  *
  29  * $FreeBSD: src/lib/libc/gen/telldir.c,v 1.4.12.1 2001/03/05 09:39:59 obrien Exp $
  30  *
  31  * @(#)telldir.c        8.1 (Berkeley) 6/4/93
  32  */
  33
  34 #include "namespace.h"
  35 #include <sys/param.h>
  36 #include <dirent.h>
  37 #include <pthread.h>
  38 #include <stdlib.h>
  39 #include <unistd.h>
  40 #include "un-namespace.h"
  41
  42 #include "libc_private.h"
  43 #include "gen_private.h"
  44
  45 /*
  46  * One of these structures is malloced to describe the current directory
  47  * position each time telldir is called. It records the current magic
  48  * cookie returned by getdirentries and the offset within the buffer
  49  * associated with that return value.
  50  */
  51 struct ddloc {
  52         struct  ddloc *loc_next;/* next structure in list */
  53         long    loc_index;      /* key associated with structure */
  54         off_t   loc_seek;       /* magic cookie returned by getdirentries */
  55         long    loc_loc;        /* offset of entry in buffer */
  56         const DIR* loc_dirp;    /* directory which used this entry */
  57 };
  58
  59 #define NDIRHASH        32      /* Num of hash lists, must be a power of 2 */
  60 #define LOCHASH(i)      ((i)&(NDIRHASH-1))
  61
  62 static long     dd_loccnt;      /* Index of entry for sequential readdir's */
  63 static struct   ddloc *dd_hash[NDIRHASH];   /* Hash list heads for ddlocs */
  64 static pthread_mutex_t dd_hash_lock;
  65
  66 /*
  67  * return a pointer into a directory
  68  */
  69 long
  70 telldir(DIR *dirp)
  71 {
  72         long index;
  73         struct ddloc *lp;
  74
  75         if (__isthreaded) {
  76                 _pthread_mutex_lock(&dirp->dd_lock);
  77                 _pthread_mutex_lock(&dd_hash_lock);
  78         }
  79
  80         /*
  81          * Reduce memory use by reusing a ddloc that might already exist
  82          * for this position.
  83          */
  84         for (lp = dd_hash[LOCHASH(dirp->dd_lastseek)]; lp; lp = lp->loc_next) {
  85                 if (lp->loc_dirp == dirp && lp->loc_seek == dirp->dd_seek &&
  86                     lp->loc_loc == dirp->dd_loc) {
  87                         index = lp->loc_index;
  88                         goto done;
  89                 }
  90         }
  91
  92         if ((lp = (struct ddloc *)malloc(sizeof(struct ddloc))) == NULL) {
  93                 index = -1;
  94                 goto done;
  95         }
  96         index = dd_loccnt++;
  97         lp->loc_index = index;
  98         lp->loc_seek = dirp->dd_seek;
  99         lp->loc_loc = dirp->dd_loc;
 100         lp->loc_dirp = dirp;
 101
 102         lp->loc_next = dd_hash[LOCHASH(index)];
 103         dd_hash[LOCHASH(index)] = lp;
 104
 105 done:
 106         if (__isthreaded) {
 107                 _pthread_mutex_unlock(&dd_hash_lock);
 108                 _pthread_mutex_unlock(&dirp->dd_lock);
 109         }
 110         return (index);
 111 }
 112
 113 /*
 114  * seek to an entry in a directory.
 115  * Only values returned by "telldir" should be passed to seekdir.
 116  */
 117 void
 118 _seekdir(DIR *dirp, long loc)
 119 {
 120         struct ddloc *lp;
 121         struct dirent *dp;
 122
 123         if (__isthreaded)
 124                 _pthread_mutex_lock(&dd_hash_lock);
 125         for (lp = dd_hash[LOCHASH(loc)]; lp; lp = lp->loc_next) {
 126                 if (lp->loc_dirp == dirp && lp->loc_index == loc)
 127                         break;
 128         }
 129         if (__isthreaded)
 130                 _pthread_mutex_unlock(&dd_hash_lock);
 131         if (lp == NULL)
 132                 return;
 133         if (lp->loc_loc == dirp->dd_loc && lp->loc_seek == dirp->dd_seek)
 134                 return;
 135         lseek(dirp->dd_fd, lp->loc_seek, SEEK_SET);
 136         dirp->dd_seek = lp->loc_seek;
 137         dirp->dd_loc = 0;
 138         dirp->dd_lastseek = loc;
 139
 140         /*
 141          * Scan the buffer until we find dd_loc.  If the directory
 142          * changed between the tell and seek it is possible to
 143          * load a new buffer or for dd_loc to not match directly.
 144          */
 145         while (dirp->dd_loc < lp->loc_loc && dirp->dd_seek == lp->loc_seek) {
 146                 dp = _readdir_unlocked(dirp, 0);
 147                 if (dp == NULL)
 148                         break;
 149         }
 150 }
 151
 152 /*
 153  * Reclaim memory for telldir cookies which weren't used.
 154  */
 155 void
 156 _reclaim_telldir(DIR *dirp)
 157 {
 158         struct ddloc *lp;
 159         struct ddloc **prevlp;
 160         int i;
 161
 162         if (__isthreaded)
 163                 _pthread_mutex_lock(&dd_hash_lock);
 164         for (i = 0; i < NDIRHASH; i++) {
 165                 prevlp = &dd_hash[i];
 166                 lp = *prevlp;
 167                 while (lp != NULL) {
 168                         if (lp->loc_dirp == dirp) {
 169                                 *prevlp = lp->loc_next;
 170                                 free((caddr_t)lp);
 171                                 lp = *prevlp;
 172                                 continue;
 173                         }
 174                         prevlp = &lp->loc_next;
 175                         lp = lp->loc_next;
 176                 }
 177         }
 178         if (__isthreaded)
 179                 _pthread_mutex_unlock(&dd_hash_lock);
 180 }