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. All advertising materials mentioning features or use of this software
  14  *    must display the following acknowledgement:
  15  *      This product includes software developed by the University of
  16  *      California, Berkeley and its contributors.
  17  * 4. Neither the name of the University nor the names of its contributors
  18  *    may be used to endorse or promote products derived from this software
  19  *    without specific prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  31  * SUCH DAMAGE.
  32  *
  33  * $FreeBSD: src/lib/libc/gen/telldir.c,v 1.4.12.1 2001/03/05 09:39:59 obrien Exp $
  34  * $DragonFly: src/lib/libc/gen/telldir.c,v 1.7 2008/05/03 22:07:37 dillon Exp $
  35  *
  36  * @(#)telldir.c        8.1 (Berkeley) 6/4/93
  37  */
  38
  39 #include "namespace.h"
  40 #include <sys/param.h>
  41 #include <dirent.h>
  42 #include <pthread.h>
  43 #include <stdlib.h>
  44 #include <unistd.h>
  45 #include "un-namespace.h"
  46
  47 #include "libc_private.h"
  48
  49 /*
  50  * One of these structures is malloced to describe the current directory
  51  * position each time telldir is called. It records the current magic
  52  * cookie returned by getdirentries and the offset within the buffer
  53  * associated with that return value.
  54  */
  55 struct ddloc {
  56         struct  ddloc *loc_next;/* next structure in list */
  57         long    loc_index;      /* key associated with structure */
  58         off_t   loc_seek;       /* magic cookie returned by getdirentries */
  59         long    loc_loc;        /* offset of entry in buffer */
  60         const DIR* loc_dirp;    /* directory which used this entry */
  61 };
  62
  63 #define NDIRHASH        32      /* Num of hash lists, must be a power of 2 */
  64 #define LOCHASH(i)      ((i)&(NDIRHASH-1))
  65
  66 static long     dd_loccnt;      /* Index of entry for sequential readdir's */
  67 static struct   ddloc *dd_hash[NDIRHASH];   /* Hash list heads for ddlocs */
  68 static pthread_mutex_t dd_hash_lock;
  69
  70 /*
  71  * return a pointer into a directory
  72  */
  73 long
  74 telldir(DIR *dirp)
  75 {
  76         long index;
  77         struct ddloc *lp;
  78
  79         if (__isthreaded) {
  80                 _pthread_mutex_lock((pthread_mutex_t *)&dirp->dd_lock);
  81                 _pthread_mutex_lock(&dd_hash_lock);
  82         }
  83
  84         /*
  85          * Reduce memory use by reusing a ddloc that might already exist
  86          * for this position.
  87          */
  88         for (lp = dd_hash[LOCHASH(dirp->dd_lastseek)]; lp; lp = lp->loc_next) {
  89                 if (lp->loc_dirp == dirp && lp->loc_seek == dirp->dd_seek &&
  90                     lp->loc_loc == dirp->dd_loc) {
  91                         index = lp->loc_index;
  92                         goto done;
  93                 }
  94         }
  95
  96         if ((lp = (struct ddloc *)malloc(sizeof(struct ddloc))) == NULL) {
  97                 index = -1;
  98                 goto done;
  99         }
 100         index = dd_loccnt++;
 101         lp->loc_index = index;
 102         lp->loc_seek = dirp->dd_seek;
 103         lp->loc_loc = dirp->dd_loc;
 104         lp->loc_dirp = dirp;
 105
 106         lp->loc_next = dd_hash[LOCHASH(index)];
 107         dd_hash[LOCHASH(index)] = lp;
 108
 109 done:
 110         if (__isthreaded) {
 111                 _pthread_mutex_unlock(&dd_hash_lock);
 112                 _pthread_mutex_unlock((pthread_mutex_t *)&dirp->dd_lock);
 113         }
 114         return (index);
 115 }
 116
 117 /*
 118  * seek to an entry in a directory.
 119  * Only values returned by "telldir" should be passed to seekdir.
 120  */
 121 void
 122 _seekdir(DIR *dirp, long loc)
 123 {
 124         struct ddloc *lp;
 125         struct dirent *dp;
 126
 127         if (__isthreaded)
 128                 _pthread_mutex_lock(&dd_hash_lock);
 129         for (lp = dd_hash[LOCHASH(loc)]; lp; lp = lp->loc_next) {
 130                 if (lp->loc_dirp == dirp && lp->loc_index == loc)
 131                         break;
 132         }
 133         if (__isthreaded)
 134                 _pthread_mutex_unlock(&dd_hash_lock);
 135         if (lp == NULL)
 136                 return;
 137         if (lp->loc_loc == dirp->dd_loc && lp->loc_seek == dirp->dd_seek)
 138                 return;
 139         lseek(dirp->dd_fd, lp->loc_seek, SEEK_SET);
 140         dirp->dd_seek = lp->loc_seek;
 141         dirp->dd_loc = 0;
 142         dirp->dd_lastseek = loc;
 143
 144         /*
 145          * Scan the buffer until we find dd_loc.  If the directory
 146          * changed between the tell and seek it is possible to
 147          * load a new buffer or for dd_loc to not match directly.
 148          */
 149         while (dirp->dd_loc < lp->loc_loc && dirp->dd_seek == lp->loc_seek) {
 150                 dp = _readdir_unlocked(dirp, 0);
 151                 if (dp == NULL)
 152                         break;
 153         }
 154 }
 155
 156 /*
 157  * Reclaim memory for telldir cookies which weren't used.
 158  */
 159 void
 160 _reclaim_telldir(DIR *dirp)
 161 {
 162         struct ddloc *lp;
 163         struct ddloc **prevlp;
 164         int i;
 165
 166         if (__isthreaded)
 167                 _pthread_mutex_lock(&dd_hash_lock);
 168         for (i = 0; i < NDIRHASH; i++) {
 169                 prevlp = &dd_hash[i];
 170                 lp = *prevlp;
 171                 while (lp != NULL) {
 172                         if (lp->loc_dirp == dirp) {
 173                                 *prevlp = lp->loc_next;
 174                                 free((caddr_t)lp);
 175                                 lp = *prevlp;
 176                                 continue;
 177                         }
 178                         prevlp = &lp->loc_next;
 179                         lp = lp->loc_next;
 180                 }
 181         }
 182         if (__isthreaded)
 183                 _pthread_mutex_unlock(&dd_hash_lock);
 184 }