nscd/cache.c

   1 /* Copyright (c) 1998, 1999 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1998.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Library General Public License as
   7    published by the Free Software Foundation; either version 2 of the
   8    License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Library General Public License for more details.
  14
  15    You should have received a copy of the GNU Library General Public
  16    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  17    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  18    Boston, MA 02111-1307, USA. */
  19
  20 #include <atomicity.h>
  21 #include <errno.h>
  22 #include <error.h>
  23 #include <limits.h>
  24 #include <stdlib.h>
  25 #include <string.h>
  26 #include <arpa/inet.h>
  27 #include <rpcsvc/nis.h>
  28 #include <sys/param.h>
  29 #include <sys/stat.h>
  30 #include <sys/uio.h>
  31
  32 #include "nscd.h"
  33 #include "dbg_log.h"
  34
  35 /* Search the cache for a matching entry and return it when found.  If
  36    this fails search the negative cache and return (void *) -1 if this
  37    search was successful.  Otherwise return NULL.
  38
  39    This function must be called with the read-lock held.  */
  40 struct hashentry *
  41 cache_search (int type, void *key, size_t len, struct database *table)
  42 {
  43   unsigned long int hash = __nis_hash (key, len) % table->module;
  44   struct hashentry *work;
  45
  46   work = table->array[hash];
  47
  48   while (work != NULL)
  49     {
  50       if (type == work->type
  51           && len == work->len && memcmp (key, work->key, len) == 0)
  52         {
  53           /* We found the entry.  Increment the appropriate counter.  */
  54           if (work->data == (void *) -1)
  55             ++table->neghit;
  56           else
  57             ++table->poshit;
  58
  59           return work;
  60         }
  61
  62       work = work->next;
  63     }
  64
  65   return NULL;
  66 }
  67
  68 /* Add a new entry to the cache.  The return value is zero if the function
  69    call was successful.
  70
  71    This function must be called with the read-lock held.
  72
  73    We modify the table but we nevertheless only acquire a read-lock.
  74    This is ok since we use operations which would be safe even without
  75    locking, given that the `prune_cache' function never runs.  Using
  76    the readlock reduces the chance of conflicts.  */
  77 void
  78 cache_add (int type, void *key, size_t len, const void *packet, size_t total,
  79            void *data, int last, time_t t, struct database *table)
  80 {
  81   unsigned long int hash = __nis_hash (key, len) % table->module;
  82   struct hashentry *newp;
  83
  84   newp = malloc (sizeof (struct hashentry));
  85   if (newp == NULL)
  86     error (EXIT_FAILURE, errno, _("while allocating hash table entry"));
  87
  88   newp->type = type;
  89   newp->len = len;
  90   newp->key = key;
  91   newp->data = data;
  92   newp->timeout = t;
  93   newp->packet = packet;
  94   newp->total = total;
  95
  96   newp->last = last;
  97
  98   /* Put the new entry in the first position.  */
  99   do
 100     newp->next = table->array[hash];
 101   while (! compare_and_swap ((volatile long int *) &table->array[hash],
 102                              (long int) newp->next, (long int) newp));
 103
 104   /* Update the statistics.  */
 105   if (data == (void *) -1)
 106     ++table->negmiss;
 107   else if (last)
 108     ++table->posmiss;
 109 }
 110
 111 /* Walk through the table and remove all entries which lifetime ended.
 112
 113    We have a problem here.  To actually remove the entries we must get
 114    the write-lock.  But since we want to keep the time we have the
 115    lock as short as possible we cannot simply acquire the lock when we
 116    start looking for timedout entries.
 117
 118    Therefore we do it in two stages: first we look for entries which
 119    must be invalidated and remember them.  Then we get the lock and
 120    actually remove them.  This is complicated by the way we have to
 121    free the data structures since some hash table entries share the same
 122    data.  */
 123 void
 124 prune_cache (struct database *table, time_t now)
 125 {
 126   size_t cnt = table->module;
 127   int mark[cnt];
 128   int anything = 0;
 129   size_t first = cnt + 1;
 130   size_t last = 0;
 131
 132   /* If this table is not actually used don't do anything.  */
 133   if (cnt == 0)
 134     return;
 135
 136   /* If we check for the modification of the underlying file we invalidate
 137      the entries also in this case.  */
 138   if (table->check_file)
 139     {
 140       struct stat st;
 141
 142       if (stat (table->filename, &st) < 0)
 143         {
 144           char buf[128];
 145           /* We cannot stat() the file, disable file checking if the
 146              file does not exist.  */
 147           dbg_log (_("cannot stat() file `%s': %s"),
 148                    table->filename, strerror_r (errno, buf, sizeof (buf)));
 149           if (errno == ENOENT)
 150             table->check_file = 0;
 151         }
 152       else
 153         {
 154           if (st.st_mtime != table->file_mtime)
 155             {
 156               /* The file changed.  Invalidate all entries.  */
 157               now = LONG_MAX;
 158               table->file_mtime = st.st_mtime;
 159             }
 160         }
 161     }
 162
 163   /* We run through the table and find values which are not valid anymore.
 164
 165    Note that for the initial step, finding the entries to be removed,
 166    we don't need to get any lock.  It is at all timed assured that the
 167    linked lists are set up correctly and that no second thread prunes
 168    the cache.  */
 169   do
 170     {
 171       struct hashentry *runp = table->array[--cnt];
 172
 173       mark[cnt] = 0;
 174
 175       while (runp != NULL)
 176         {
 177           if (runp->timeout < now)
 178             {
 179               ++mark[cnt];
 180               anything = 1;
 181               first = MIN (first, cnt);
 182               last = MAX (last, cnt);
 183             }
 184           runp = runp->next;
 185         }
 186     }
 187   while (cnt > 0);
 188
 189   if (anything)
 190     {
 191       struct hashentry *head = NULL;
 192
 193       /* Now we have to get the write lock since we are about to modify
 194          the table.  */
 195       pthread_rwlock_wrlock (&table->lock);
 196
 197       while (first <= last)
 198         {
 199           if (mark[first] > 0)
 200             {
 201               struct hashentry *runp;
 202
 203               while (table->array[first]->timeout < now)
 204                 {
 205                   table->array[first]->dellist = head;
 206                   head = table->array[first];
 207                   table->array[first] = head->next;
 208                   if (--mark[first] == 0)
 209                     break;
 210                 }
 211
 212               runp = table->array[first];
 213               while (mark[first] > 0)
 214                 {
 215                   if (runp->next->timeout < now)
 216                     {
 217                       runp->next->dellist = head;
 218                       head = runp->next;
 219                       runp->next = head->next;
 220                       --mark[first];
 221                     }
 222                   else
 223                     runp = runp->next;
 224                 }
 225             }
 226           ++first;
 227         }
 228
 229       /* It's all done.  */
 230       pthread_rwlock_unlock (&table->lock);
 231
 232       /* And another run to free the data.  */
 233       do
 234         {
 235           struct hashentry *old = head;
 236
 237           if (debug_level > 0)
 238             {
 239               char buf[INET6_ADDRSTRLEN];
 240               const char *str;
 241
 242               if ((old->type == GETHOSTBYADDR || old->type == GETHOSTBYADDRv6)
 243                   && (old->last || old->data == (void *) -1))
 244                 {
 245                   inet_ntop (old->type == GETHOSTBYADDR ? AF_INET : AF_INET6,
 246                              old->key, buf, sizeof (buf));
 247                   str = buf;
 248                 }
 249               else
 250                 str = old->last ? old->key : (old->data == (void *) -1
 251                                               ? old->key : "???");
 252
 253               dbg_log ("remove %s entry \"%s\"", serv2str[old->type], str);
 254             }
 255
 256           /* Free the data structures.  */
 257           if (old->data == (void *) -1)
 258             free (old->key);
 259           else if (old->last)
 260             free (old->data);
 261
 262           head = head->dellist;
 263
 264           free (old);
 265         }
 266       while (head != NULL);
 267     }
 268 }