ap/libc/glibc/glibc-2.23/nscd/cache.c - T106_DC - Gitiles

 /* Copyright (c) 1998-2016 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1998.

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published
    by the Free Software Foundation; version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, see <http://www.gnu.org/licenses/>.  */

 #include <assert.h>
 #include <atomic.h>
 #include <errno.h>
 #include <error.h>
 #include <inttypes.h>
 #include <limits.h>
 #include <stdlib.h>
 #include <string.h>
 #include <libintl.h>
 #include <arpa/inet.h>
 #include <rpcsvc/nis.h>
 #include <sys/mman.h>
 #include <sys/param.h>
 #include <sys/stat.h>
 #include <sys/uio.h>

 #include "nscd.h"
 #include "dbg_log.h"


 /* Wrapper functions with error checking for standard functions.  */
 extern void *xcalloc (size_t n, size_t s);


 /* Number of times a value is reloaded without being used.  UINT_MAX
    means unlimited.  */
 unsigned int reload_count = DEFAULT_RELOAD_LIMIT;


 static time_t (*const readdfcts[LASTREQ]) (struct database_dyn *,
 					   struct hashentry *,
 					   struct datahead *) =
 {
   [GETPWBYNAME] = readdpwbyname,
   [GETPWBYUID] = readdpwbyuid,
   [GETGRBYNAME] = readdgrbyname,
   [GETGRBYGID] = readdgrbygid,
   [GETHOSTBYNAME] = readdhstbyname,
   [GETHOSTBYNAMEv6] = readdhstbynamev6,
   [GETHOSTBYADDR] = readdhstbyaddr,
   [GETHOSTBYADDRv6] = readdhstbyaddrv6,
   [GETAI] = readdhstai,
   [INITGROUPS] = readdinitgroups,
   [GETSERVBYNAME] = readdservbyname,
   [GETSERVBYPORT] = readdservbyport,
   [GETNETGRENT] = readdgetnetgrent,
   [INNETGR] = readdinnetgr
 };


 /* Search the cache for a matching entry and return it when found.  If
    this fails search the negative cache and return (void *) -1 if this
    search was successful.  Otherwise return NULL.

    This function must be called with the read-lock held.  */
 struct datahead *
 cache_search (request_type type, const void *key, size_t len,
 	      struct database_dyn *table, uid_t owner)
 {
   unsigned long int hash = __nis_hash (key, len) % table->head->module;

   unsigned long int nsearched = 0;
   struct datahead *result = NULL;

   ref_t work = table->head->array[hash];
   while (work != ENDREF)
     {
       ++nsearched;

       struct hashentry *here = (struct hashentry *) (table->data + work);

       if (type == here->type && len == here->len
 	  && memcmp (key, table->data + here->key, len) == 0
 	  && here->owner == owner)
 	{
 	  /* We found the entry.  Increment the appropriate counter.  */
 	  struct datahead *dh
 	    = (struct datahead *) (table->data + here->packet);

 	  /* See whether we must ignore the entry.  */
 	  if (dh->usable)
 	    {
 	      /* We do not synchronize the memory here.  The statistics
 		 data is not crucial, we synchronize only once in a while
 		 in the cleanup threads.  */
 	      if (dh->notfound)
 		++table->head->neghit;
 	      else
 		{
 		  ++table->head->poshit;

 		  if (dh->nreloads != 0)
 		    dh->nreloads = 0;
 		}

 	      result = dh;
 	      break;
 	    }
 	}

       work = here->next;
     }

   if (nsearched > table->head->maxnsearched)
     table->head->maxnsearched = nsearched;

   return result;
 }

 /* Add a new entry to the cache.  The return value is zero if the function
    call was successful.

    This function must be called with the read-lock held.

    We modify the table but we nevertheless only acquire a read-lock.
    This is ok since we use operations which would be safe even without
    locking, given that the `prune_cache' function never runs.  Using
    the readlock reduces the chance of conflicts.  */
 int
 cache_add (int type, const void *key, size_t len, struct datahead *packet,
 	   bool first, struct database_dyn *table,
 	   uid_t owner, bool prune_wakeup)
 {
   if (__glibc_unlikely (debug_level >= 2))
     {
       const char *str;
       char buf[INET6_ADDRSTRLEN + 1];
       if (type == GETHOSTBYADDR || type == GETHOSTBYADDRv6)
 	str = inet_ntop (type == GETHOSTBYADDR ? AF_INET : AF_INET6,
 			 key, buf, sizeof (buf));
       else
 	str = key;

       dbg_log (_("add new entry \"%s\" of type %s for %s to cache%s"),
 	       str, serv2str[type], dbnames[table - dbs],
 	       first ? _(" (first)") : "");
     }

   unsigned long int hash = __nis_hash (key, len) % table->head->module;
   struct hashentry *newp;

   newp = mempool_alloc (table, sizeof (struct hashentry), 0);
   /* If we cannot allocate memory, just do not do anything.  */
   if (newp == NULL)
     {
       /* If necessary mark the entry as unusable so that lookups will
 	 not use it.  */
       if (first)
 	packet->usable = false;

       return -1;
     }

   newp->type = type;
   newp->first = first;
   newp->len = len;
   newp->key = (char *) key - table->data;
   assert (newp->key + newp->len <= table->head->first_free);
   newp->owner = owner;
   newp->packet = (char *) packet - table->data;
   assert ((newp->packet & BLOCK_ALIGN_M1) == 0);

   /* Put the new entry in the first position.  */
   do
     newp->next = table->head->array[hash];
   while (atomic_compare_and_exchange_bool_rel (&table->head->array[hash],
 					       (ref_t) ((char *) newp
 							- table->data),
 					       (ref_t) newp->next));

   /* Update the statistics.  */
   if (packet->notfound)
     ++table->head->negmiss;
   else if (first)
     ++table->head->posmiss;

   /* We depend on this value being correct and at least as high as the
      real number of entries.  */
   atomic_increment (&table->head->nentries);

   /* It does not matter that we are not loading the just increment
      value, this is just for statistics.  */
   unsigned long int nentries = table->head->nentries;
   if (nentries > table->head->maxnentries)
     table->head->maxnentries = nentries;

   if (table->persistent)
     // XXX async OK?
     msync ((void *) table->head,
 	   (char *) &table->head->array[hash] - (char *) table->head
 	   + sizeof (ref_t), MS_ASYNC);

   /* We do not have to worry about the pruning thread if we are
      re-adding the data since this is done by the pruning thread.  We
      also do not have to do anything in case this is not the first
      time the data is entered since different data heads all have the
      same timeout.  */
   if (first && prune_wakeup)
     {
       /* Perhaps the prune thread for the table is not running in a long
 	 time.  Wake it if necessary.  */
       pthread_mutex_lock (&table->prune_lock);
       time_t next_wakeup = table->wakeup_time;
       bool do_wakeup = false;
       if (next_wakeup > packet->timeout + CACHE_PRUNE_INTERVAL)
 	{
 	  table->wakeup_time = packet->timeout;
 	  do_wakeup = true;
 	}
       pthread_mutex_unlock (&table->prune_lock);
       if (do_wakeup)
 	pthread_cond_signal (&table->prune_cond);
     }

   return 0;
 }

 /* Walk through the table and remove all entries which lifetime ended.

    We have a problem here.  To actually remove the entries we must get
    the write-lock.  But since we want to keep the time we have the
    lock as short as possible we cannot simply acquire the lock when we
    start looking for timedout entries.

    Therefore we do it in two stages: first we look for entries which
    must be invalidated and remember them.  Then we get the lock and
    actually remove them.  This is complicated by the way we have to
    free the data structures since some hash table entries share the same
    data.  */
 time_t
 prune_cache (struct database_dyn *table, time_t now, int fd)
 {
   size_t cnt = table->head->module;

   /* If this table is not actually used don't do anything.  */
   if (cnt == 0)
     {
       if (fd != -1)
 	{
 	  /* Reply to the INVALIDATE initiator.  */
 	  int32_t resp = 0;
 	  writeall (fd, &resp, sizeof (resp));
 	}

       /* No need to do this again anytime soon.  */
       return 24 * 60 * 60;
     }

   /* If we check for the modification of the underlying file we invalidate
      the entries also in this case.  */
   if (table->check_file && now != LONG_MAX)
     {
       struct traced_file *runp = table->traced_files;

       while (runp != NULL)
 	{
 #ifdef HAVE_INOTIFY
 	  if (runp->inotify_descr[TRACED_FILE] == -1)
 #endif
 	    {
 	      struct stat64 st;

 	      if (stat64 (runp->fname, &st) < 0)
 		{
 		  /* Print a diagnostic that the traced file was missing.
 		     We must not disable tracing since the file might return
 		     shortly and we want to reload it at the next pruning.
 		     Disabling tracing here would go against the configuration
 		     as specified by the user via check-files.  */
 		  char buf[128];
 		  dbg_log (_("checking for monitored file `%s': %s"),
 			   runp->fname, strerror_r (errno, buf, sizeof (buf)));
 		}
 	      else
 		{
 		  /* This must be `!=` to catch cases where users turn the
 		     clocks back and we still want to detect any time difference
 		     in mtime.  */
 		  if (st.st_mtime != runp->mtime)
 		    {
 		      dbg_log (_("monitored file `%s` changed (mtime)"),
 			       runp->fname);
 		      /* The file changed. Invalidate all entries.  */
 		      now = LONG_MAX;
 		      runp->mtime = st.st_mtime;
 #ifdef HAVE_INOTIFY
 		      /* Attempt to install a watch on the file.  */
 		      install_watches (runp);
 #endif
 		    }
 		}
 	    }

 	  runp = runp->next;
 	}
     }

   /* We run through the table and find values which are not valid anymore.

      Note that for the initial step, finding the entries to be removed,
      we don't need to get any lock.  It is at all timed assured that the
      linked lists are set up correctly and that no second thread prunes
      the cache.  */
   bool *mark;
   size_t memory_needed = cnt * sizeof (bool);
   bool mark_use_alloca;
   if (__glibc_likely (memory_needed <= MAX_STACK_USE))
     {
       mark = alloca (cnt * sizeof (bool));
       memset (mark, '\0', memory_needed);
       mark_use_alloca = true;
     }
   else
     {
       mark = xcalloc (1, memory_needed);
       mark_use_alloca = false;
     }
   size_t first = cnt + 1;
   size_t last = 0;
   char *const data = table->data;
   bool any = false;

   if (__glibc_unlikely (debug_level > 2))
     dbg_log (_("pruning %s cache; time %ld"),
 	     dbnames[table - dbs], (long int) now);

 #define NO_TIMEOUT LONG_MAX
   time_t next_timeout = NO_TIMEOUT;
   do
     {
       ref_t run = table->head->array[--cnt];

       while (run != ENDREF)
 	{
 	  struct hashentry *runp = (struct hashentry *) (data + run);
 	  struct datahead *dh = (struct datahead *) (data + runp->packet);

 	  /* Some debug support.  */
 	  if (__glibc_unlikely (debug_level > 2))
 	    {
 	      char buf[INET6_ADDRSTRLEN];
 	      const char *str;

 	      if (runp->type == GETHOSTBYADDR || runp->type == GETHOSTBYADDRv6)
 		{
 		  inet_ntop (runp->type == GETHOSTBYADDR ? AF_INET : AF_INET6,
 			     data + runp->key, buf, sizeof (buf));
 		  str = buf;
 		}
 	      else
 		str = data + runp->key;

 	      dbg_log (_("considering %s entry \"%s\", timeout %" PRIu64),
 		       serv2str[runp->type], str, dh->timeout);
 	    }

 	  /* Check whether the entry timed out.  */
 	  if (dh->timeout < now)
 	    {
 	      /* This hash bucket could contain entries which need to
 		 be looked at.  */
 	      mark[cnt] = true;

 	      first = MIN (first, cnt);
 	      last = MAX (last, cnt);

 	      /* We only have to look at the data of the first entries
 		 since the count information is kept in the data part
 		 which is shared.  */
 	      if (runp->first)
 		{

 		  /* At this point there are two choices: we reload the
 		     value or we discard it.  Do not change NRELOADS if
 		     we never not reload the record.  */
 		  if ((reload_count != UINT_MAX
 		       && __builtin_expect (dh->nreloads >= reload_count, 0))
 		      /* We always remove negative entries.  */
 		      || dh->notfound
 		      /* Discard everything if the user explicitly
 			 requests it.  */
 		      || now == LONG_MAX)
 		    {
 		      /* Remove the value.  */
 		      dh->usable = false;

 		      /* We definitely have some garbage entries now.  */
 		      any = true;
 		    }
 		  else
 		    {
 		      /* Reload the value.  We do this only for the
 			 initially used key, not the additionally
 			 added derived value.  */
 		      assert (runp->type < LASTREQ
 			      && readdfcts[runp->type] != NULL);

 		      time_t timeout = readdfcts[runp->type] (table, runp, dh);
 		      next_timeout = MIN (next_timeout, timeout);

 		      /* If the entry has been replaced, we might need
 			 cleanup.  */
 		      any |= !dh->usable;
 		    }
 		}
 	    }
 	  else
 	    {
 	      assert (dh->usable);
 	      next_timeout = MIN (next_timeout, dh->timeout);
 	    }

 	  run = runp->next;
 	}
     }
   while (cnt > 0);

   if (__glibc_unlikely (fd != -1))
     {
       /* Reply to the INVALIDATE initiator that the cache has been
 	 invalidated.  */
       int32_t resp = 0;
       writeall (fd, &resp, sizeof (resp));
     }

   if (first <= last)
     {
       struct hashentry *head = NULL;

       /* Now we have to get the write lock since we are about to modify
 	 the table.  */
       if (__glibc_unlikely (pthread_rwlock_trywrlock (&table->lock) != 0))
 	{
 	  ++table->head->wrlockdelayed;
 	  pthread_rwlock_wrlock (&table->lock);
 	}

       while (first <= last)
 	{
 	  if (mark[first])
 	    {
 	      ref_t *old = &table->head->array[first];
 	      ref_t run = table->head->array[first];

 	      assert (run != ENDREF);
 	      do
 		{
 		  struct hashentry *runp = (struct hashentry *) (data + run);
 		  struct datahead *dh
 		    = (struct datahead *) (data + runp->packet);

 		  if (! dh->usable)
 		    {
 		      /* We need the list only for debugging but it is
 			 more costly to avoid creating the list than
 			 doing it.  */
 		      runp->dellist = head;
 		      head = runp;

 		      /* No need for an atomic operation, we have the
 			 write lock.  */
 		      --table->head->nentries;

 		      run = *old = runp->next;
 		    }
 		  else
 		    {
 		      old = &runp->next;
 		      run = runp->next;
 		    }
 		}
 	      while (run != ENDREF);
 	    }

 	  ++first;
 	}

       /* It's all done.  */
       pthread_rwlock_unlock (&table->lock);

       /* Make sure the data is saved to disk.  */
       if (table->persistent)
 	msync (table->head,
 	       data + table->head->first_free - (char *) table->head,
 	       MS_ASYNC);

       /* One extra pass if we do debugging.  */
       if (__glibc_unlikely (debug_level > 0))
 	{
 	  struct hashentry *runp = head;

 	  while (runp != NULL)
 	    {
 	      char buf[INET6_ADDRSTRLEN];
 	      const char *str;

 	      if (runp->type == GETHOSTBYADDR || runp->type == GETHOSTBYADDRv6)
 		{
 		  inet_ntop (runp->type == GETHOSTBYADDR ? AF_INET : AF_INET6,
 			     data + runp->key, buf, sizeof (buf));
 		  str = buf;
 		}
 	      else
 		str = data + runp->key;

 	      dbg_log ("remove %s entry \"%s\"", serv2str[runp->type], str);

 	      runp = runp->dellist;
 	    }
 	}
     }

   if (__glibc_unlikely (! mark_use_alloca))
     free (mark);

   /* Run garbage collection if any entry has been removed or replaced.  */
   if (any)
     gc (table);

   /* If there is no entry in the database and we therefore have no new
      timeout value, tell the caller to wake up in 24 hours.  */
   return next_timeout == NO_TIMEOUT ? 24 * 60 * 60 : next_timeout - now;
 }
	/* Copyright (c) 1998-2016 Free Software Foundation, Inc.
	This file is part of the GNU C Library.
	Contributed by Ulrich Drepper <drepper@cygnus.com>, 1998.

	This program is free software; you can redistribute it and/or modify
	it under the terms of the GNU General Public License as published
	by the Free Software Foundation; version 2 of the License, or
	(at your option) any later version.

	This program is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	GNU General Public License for more details.

	You should have received a copy of the GNU General Public License
	along with this program; if not, see <http://www.gnu.org/licenses/>. */

	#include <assert.h>
	#include <atomic.h>
	#include <errno.h>
	#include <error.h>
	#include <inttypes.h>
	#include <limits.h>
	#include <stdlib.h>
	#include <string.h>
	#include <libintl.h>
	#include <arpa/inet.h>
	#include <rpcsvc/nis.h>
	#include <sys/mman.h>
	#include <sys/param.h>
	#include <sys/stat.h>
	#include <sys/uio.h>

	#include "nscd.h"
	#include "dbg_log.h"


	/* Wrapper functions with error checking for standard functions. */
	extern void *xcalloc (size_t n, size_t s);


	/* Number of times a value is reloaded without being used. UINT_MAX
	means unlimited. */
	unsigned int reload_count = DEFAULT_RELOAD_LIMIT;


	static time_t (const readdfcts[LASTREQ]) (struct database_dyn ,
	struct hashentry *,
	struct datahead *) =
	{
	[GETPWBYNAME] = readdpwbyname,
	[GETPWBYUID] = readdpwbyuid,
	[GETGRBYNAME] = readdgrbyname,
	[GETGRBYGID] = readdgrbygid,
	[GETHOSTBYNAME] = readdhstbyname,
	[GETHOSTBYNAMEv6] = readdhstbynamev6,
	[GETHOSTBYADDR] = readdhstbyaddr,
	[GETHOSTBYADDRv6] = readdhstbyaddrv6,
	[GETAI] = readdhstai,
	[INITGROUPS] = readdinitgroups,
	[GETSERVBYNAME] = readdservbyname,
	[GETSERVBYPORT] = readdservbyport,
	[GETNETGRENT] = readdgetnetgrent,
	[INNETGR] = readdinnetgr
	};


	/* Search the cache for a matching entry and return it when found. If
	this fails search the negative cache and return (void *) -1 if this
	search was successful. Otherwise return NULL.

	This function must be called with the read-lock held. */
	struct datahead *
	cache_search (request_type type, const void *key, size_t len,
	struct database_dyn *table, uid_t owner)
	{
	unsigned long int hash = __nis_hash (key, len) % table->head->module;

	unsigned long int nsearched = 0;
	struct datahead *result = NULL;

	ref_t work = table->head->array[hash];
	while (work != ENDREF)
	{
	++nsearched;

	struct hashentry here = (struct hashentry ) (table->data + work);

	if (type == here->type && len == here->len
	&& memcmp (key, table->data + here->key, len) == 0
	&& here->owner == owner)
	{
	/* We found the entry. Increment the appropriate counter. */
	struct datahead *dh
	= (struct datahead *) (table->data + here->packet);

	/* See whether we must ignore the entry. */
	if (dh->usable)
	{
	/* We do not synchronize the memory here. The statistics
	data is not crucial, we synchronize only once in a while
	in the cleanup threads. */
	if (dh->notfound)
	++table->head->neghit;
	else
	{
	++table->head->poshit;

	if (dh->nreloads != 0)
	dh->nreloads = 0;
	}

	result = dh;
	break;
	}
	}

	work = here->next;
	}

	if (nsearched > table->head->maxnsearched)
	table->head->maxnsearched = nsearched;

	return result;
	}

	/* Add a new entry to the cache. The return value is zero if the function
	call was successful.

	This function must be called with the read-lock held.

	We modify the table but we nevertheless only acquire a read-lock.
	This is ok since we use operations which would be safe even without
	locking, given that the `prune_cache' function never runs. Using
	the readlock reduces the chance of conflicts. */
	int
	cache_add (int type, const void key, size_t len, struct datahead packet,
	bool first, struct database_dyn *table,
	uid_t owner, bool prune_wakeup)
	{
	if (__glibc_unlikely (debug_level >= 2))
	{
	const char *str;
	char buf[INET6_ADDRSTRLEN + 1];
	if (type == GETHOSTBYADDR \|\| type == GETHOSTBYADDRv6)
	str = inet_ntop (type == GETHOSTBYADDR ? AF_INET : AF_INET6,
	key, buf, sizeof (buf));
	else
	str = key;

	dbg_log (_("add new entry \"%s\" of type %s for %s to cache%s"),
	str, serv2str[type], dbnames[table - dbs],
	first ? _(" (first)") : "");
	}

	unsigned long int hash = __nis_hash (key, len) % table->head->module;
	struct hashentry *newp;

	newp = mempool_alloc (table, sizeof (struct hashentry), 0);
	/* If we cannot allocate memory, just do not do anything. */
	if (newp == NULL)
	{
	/* If necessary mark the entry as unusable so that lookups will
	not use it. */
	if (first)
	packet->usable = false;

	return -1;
	}

	newp->type = type;
	newp->first = first;
	newp->len = len;
	newp->key = (char *) key - table->data;
	assert (newp->key + newp->len <= table->head->first_free);
	newp->owner = owner;
	newp->packet = (char *) packet - table->data;
	assert ((newp->packet & BLOCK_ALIGN_M1) == 0);

	/* Put the new entry in the first position. */
	do
	newp->next = table->head->array[hash];
	while (atomic_compare_and_exchange_bool_rel (&table->head->array[hash],
	(ref_t) ((char *) newp
	- table->data),
	(ref_t) newp->next));

	/* Update the statistics. */
	if (packet->notfound)
	++table->head->negmiss;
	else if (first)
	++table->head->posmiss;

	/* We depend on this value being correct and at least as high as the
	real number of entries. */
	atomic_increment (&table->head->nentries);

	/* It does not matter that we are not loading the just increment
	value, this is just for statistics. */
	unsigned long int nentries = table->head->nentries;
	if (nentries > table->head->maxnentries)
	table->head->maxnentries = nentries;

	if (table->persistent)
	// XXX async OK?
	msync ((void *) table->head,
	(char ) &table->head->array[hash] - (char ) table->head
	+ sizeof (ref_t), MS_ASYNC);

	/* We do not have to worry about the pruning thread if we are
	re-adding the data since this is done by the pruning thread. We
	also do not have to do anything in case this is not the first
	time the data is entered since different data heads all have the
	same timeout. */
	if (first && prune_wakeup)
	{
	/* Perhaps the prune thread for the table is not running in a long
	time. Wake it if necessary. */
	pthread_mutex_lock (&table->prune_lock);
	time_t next_wakeup = table->wakeup_time;
	bool do_wakeup = false;
	if (next_wakeup > packet->timeout + CACHE_PRUNE_INTERVAL)
	{
	table->wakeup_time = packet->timeout;
	do_wakeup = true;
	}
	pthread_mutex_unlock (&table->prune_lock);
	if (do_wakeup)
	pthread_cond_signal (&table->prune_cond);
	}

	return 0;
	}

	/* Walk through the table and remove all entries which lifetime ended.

	We have a problem here. To actually remove the entries we must get
	the write-lock. But since we want to keep the time we have the
	lock as short as possible we cannot simply acquire the lock when we
	start looking for timedout entries.

	Therefore we do it in two stages: first we look for entries which
	must be invalidated and remember them. Then we get the lock and
	actually remove them. This is complicated by the way we have to
	free the data structures since some hash table entries share the same
	data. */
	time_t
	prune_cache (struct database_dyn *table, time_t now, int fd)
	{
	size_t cnt = table->head->module;

	/* If this table is not actually used don't do anything. */
	if (cnt == 0)
	{
	if (fd != -1)
	{
	/* Reply to the INVALIDATE initiator. */
	int32_t resp = 0;
	writeall (fd, &resp, sizeof (resp));
	}

	/* No need to do this again anytime soon. */
	return 24 * 60 * 60;
	}

	/* If we check for the modification of the underlying file we invalidate
	the entries also in this case. */
	if (table->check_file && now != LONG_MAX)
	{
	struct traced_file *runp = table->traced_files;

	while (runp != NULL)
	{
	#ifdef HAVE_INOTIFY
	if (runp->inotify_descr[TRACED_FILE] == -1)
	#endif
	{
	struct stat64 st;

	if (stat64 (runp->fname, &st) < 0)
	{
	/* Print a diagnostic that the traced file was missing.
	We must not disable tracing since the file might return
	shortly and we want to reload it at the next pruning.
	Disabling tracing here would go against the configuration
	as specified by the user via check-files. */
	char buf[128];
	dbg_log (_("checking for monitored file `%s': %s"),
	runp->fname, strerror_r (errno, buf, sizeof (buf)));
	}
	else
	{
	/* This must be `!=` to catch cases where users turn the
	clocks back and we still want to detect any time difference
	in mtime. */
	if (st.st_mtime != runp->mtime)
	{
	dbg_log (_("monitored file `%s` changed (mtime)"),
	runp->fname);
	/* The file changed. Invalidate all entries. */
	now = LONG_MAX;
	runp->mtime = st.st_mtime;
	#ifdef HAVE_INOTIFY
	/* Attempt to install a watch on the file. */
	install_watches (runp);
	#endif
	}
	}
	}

	runp = runp->next;
	}
	}

	/* We run through the table and find values which are not valid anymore.

	Note that for the initial step, finding the entries to be removed,
	we don't need to get any lock. It is at all timed assured that the
	linked lists are set up correctly and that no second thread prunes
	the cache. */
	bool *mark;
	size_t memory_needed = cnt * sizeof (bool);
	bool mark_use_alloca;
	if (__glibc_likely (memory_needed <= MAX_STACK_USE))
	{
	mark = alloca (cnt * sizeof (bool));
	memset (mark, '\0', memory_needed);
	mark_use_alloca = true;
	}
	else
	{
	mark = xcalloc (1, memory_needed);
	mark_use_alloca = false;
	}
	size_t first = cnt + 1;
	size_t last = 0;
	char *const data = table->data;
	bool any = false;

	if (__glibc_unlikely (debug_level > 2))
	dbg_log (_("pruning %s cache; time %ld"),
	dbnames[table - dbs], (long int) now);

	#define NO_TIMEOUT LONG_MAX
	time_t next_timeout = NO_TIMEOUT;
	do
	{
	ref_t run = table->head->array[--cnt];

	while (run != ENDREF)
	{
	struct hashentry runp = (struct hashentry ) (data + run);
	struct datahead dh = (struct datahead ) (data + runp->packet);

	/* Some debug support. */
	if (__glibc_unlikely (debug_level > 2))
	{
	char buf[INET6_ADDRSTRLEN];
	const char *str;

	if (runp->type == GETHOSTBYADDR \|\| runp->type == GETHOSTBYADDRv6)
	{
	inet_ntop (runp->type == GETHOSTBYADDR ? AF_INET : AF_INET6,
	data + runp->key, buf, sizeof (buf));
	str = buf;
	}
	else
	str = data + runp->key;

	dbg_log (_("considering %s entry \"%s\", timeout %" PRIu64),
	serv2str[runp->type], str, dh->timeout);
	}

	/* Check whether the entry timed out. */
	if (dh->timeout < now)
	{
	/* This hash bucket could contain entries which need to
	be looked at. */
	mark[cnt] = true;

	first = MIN (first, cnt);
	last = MAX (last, cnt);

	/* We only have to look at the data of the first entries
	since the count information is kept in the data part
	which is shared. */
	if (runp->first)
	{

	/* At this point there are two choices: we reload the
	value or we discard it. Do not change NRELOADS if
	we never not reload the record. */
	if ((reload_count != UINT_MAX
	&& __builtin_expect (dh->nreloads >= reload_count, 0))
	/* We always remove negative entries. */
	\|\| dh->notfound
	/* Discard everything if the user explicitly
	requests it. */
	\|\| now == LONG_MAX)
	{
	/* Remove the value. */
	dh->usable = false;

	/* We definitely have some garbage entries now. */
	any = true;
	}
	else
	{
	/* Reload the value. We do this only for the
	initially used key, not the additionally
	added derived value. */
	assert (runp->type < LASTREQ
	&& readdfcts[runp->type] != NULL);

	time_t timeout = readdfcts[runp->type] (table, runp, dh);
	next_timeout = MIN (next_timeout, timeout);

	/* If the entry has been replaced, we might need
	cleanup. */
	any \|= !dh->usable;
	}
	}
	}
	else
	{
	assert (dh->usable);
	next_timeout = MIN (next_timeout, dh->timeout);
	}

	run = runp->next;
	}
	}
	while (cnt > 0);

	if (__glibc_unlikely (fd != -1))
	{
	/* Reply to the INVALIDATE initiator that the cache has been
	invalidated. */
	int32_t resp = 0;
	writeall (fd, &resp, sizeof (resp));
	}

	if (first <= last)
	{
	struct hashentry *head = NULL;

	/* Now we have to get the write lock since we are about to modify
	the table. */
	if (__glibc_unlikely (pthread_rwlock_trywrlock (&table->lock) != 0))
	{
	++table->head->wrlockdelayed;
	pthread_rwlock_wrlock (&table->lock);
	}

	while (first <= last)
	{
	if (mark[first])
	{
	ref_t *old = &table->head->array[first];
	ref_t run = table->head->array[first];

	assert (run != ENDREF);
	do
	{
	struct hashentry runp = (struct hashentry ) (data + run);
	struct datahead *dh
	= (struct datahead *) (data + runp->packet);

	if (! dh->usable)
	{
	/* We need the list only for debugging but it is
	more costly to avoid creating the list than
	doing it. */
	runp->dellist = head;
	head = runp;

	/* No need for an atomic operation, we have the
	write lock. */
	--table->head->nentries;

	run = *old = runp->next;
	}
	else
	{
	old = &runp->next;
	run = runp->next;
	}
	}
	while (run != ENDREF);
	}

	++first;
	}

	/* It's all done. */
	pthread_rwlock_unlock (&table->lock);

	/* Make sure the data is saved to disk. */
	if (table->persistent)
	msync (table->head,
	data + table->head->first_free - (char *) table->head,
	MS_ASYNC);

	/* One extra pass if we do debugging. */
	if (__glibc_unlikely (debug_level > 0))
	{
	struct hashentry *runp = head;

	while (runp != NULL)
	{
	char buf[INET6_ADDRSTRLEN];
	const char *str;

	if (runp->type == GETHOSTBYADDR \|\| runp->type == GETHOSTBYADDRv6)
	{
	inet_ntop (runp->type == GETHOSTBYADDR ? AF_INET : AF_INET6,
	data + runp->key, buf, sizeof (buf));
	str = buf;
	}
	else
	str = data + runp->key;

	dbg_log ("remove %s entry \"%s\"", serv2str[runp->type], str);

	runp = runp->dellist;
	}
	}
	}

	if (__glibc_unlikely (! mark_use_alloca))
	free (mark);

	/* Run garbage collection if any entry has been removed or replaced. */
	if (any)
	gc (table);

	/* If there is no entry in the database and we therefore have no new
	timeout value, tell the caller to wake up in 24 hours. */
	return next_timeout == NO_TIMEOUT ? 24 * 60 * 60 : next_timeout - now;
	}