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asyncdns.c

/*
   Unix SMB/Netbios implementation.
   a async DNS handler
   Copyright (C) Andrew Tridgell 1997-1998
   
   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; either 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, write to the Free Software
   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
   */

#include "includes.h"

/***************************************************************************
  Add a DNS result to the name cache.
****************************************************************************/

static struct name_record *add_dns_result(struct nmb_name *question, struct in_addr addr)
{
  int name_type = question->name_type;
  char *qname = question->name;
  
  
  if (!addr.s_addr) {
    /* add the fail to WINS cache of names. give it 1 hour in the cache */
    DEBUG(3,("add_dns_result: Negative DNS answer for %s\n", qname));
    (void)add_name_to_subnet( wins_server_subnet, qname, name_type,
                              NB_ACTIVE, 60*60, DNSFAIL_NAME, 1, &addr );
    return( NULL );
  }

  /* add it to our WINS cache of names. give it 2 hours in the cache */
  DEBUG(3,("add_dns_result: DNS gave answer for %s of %s\n", qname, inet_ntoa(addr)));

  return( add_name_to_subnet( wins_server_subnet, qname, name_type,
                              NB_ACTIVE, 2*60*60, DNS_NAME, 1, &addr ) );
}



#ifndef SYNC_DNS

static int fd_in = -1, fd_out = -1;
static pid_t child_pid = -1;
static int in_dns;

/* this is the structure that is passed between the parent and child */
struct query_record {
      struct nmb_name name;
      struct in_addr result;
};

/* a queue of pending requests waiting to be sent to the DNS child */
static struct packet_struct *dns_queue;

/* the packet currently being processed by the dns child */
static struct packet_struct *dns_current;


/***************************************************************************
  return the fd used to gather async dns replies. This is added to the select
  loop
  ****************************************************************************/
int asyncdns_fd(void)
{
      return fd_in;
}

/***************************************************************************
  handle DNS queries arriving from the parent
  ****************************************************************************/
static void asyncdns_process(void)
{
      struct query_record r;
      fstring qname;

      DEBUGLEVEL = -1;

      while (1) {
            if (read_data(fd_in, (char *)&r, sizeof(r)) != sizeof(r)) 
                  break;

            fstrcpy(qname, r.name.name);

            r.result.s_addr = interpret_addr(qname);

            if (write_data(fd_out, (char *)&r, sizeof(r)) != sizeof(r))
                  break;
      }

      _exit(0);
}

/**************************************************************************** **
  catch a sigterm (in the child process - the parent has a different handler
  see nmbd.c for details).
  We need a separate term handler here so we don't release any 
  names that our parent is going to release, or overwrite a 
  WINS db that our parent is going to write.
 **************************************************************************** */

static void sig_term(int sig)
{
  _exit(0);
}

/***************************************************************************
 Called by the parent process when it receives a SIGTERM - also kills the
 child so we don't get child async dns processes lying around, causing trouble.
  ****************************************************************************/

void kill_async_dns_child(void)
{
  if(child_pid != 0 && child_pid != -1)
    kill(child_pid, SIGTERM);
}

/***************************************************************************
  create a child process to handle DNS lookups
  ****************************************************************************/
void start_async_dns(void)
{
      int fd1[2], fd2[2];

      CatchChild();

      if (pipe(fd1) || pipe(fd2)) {
            DEBUG(0,("can't create asyncdns pipes\n"));
            return;
      }

      child_pid = sys_fork();

      if (child_pid) {
            fd_in = fd1[0];
            fd_out = fd2[1];
            close(fd1[1]);
            close(fd2[0]);
            DEBUG(0,("started asyncdns process %d\n", (int)child_pid));
            return;
      }

      fd_in = fd2[0];
      fd_out = fd1[1];

      CatchSignal(SIGUSR2, SIG_IGN);
      CatchSignal(SIGUSR1, SIG_IGN);
      CatchSignal(SIGHUP, SIG_IGN);
        CatchSignal(SIGTERM, SIGNAL_CAST sig_term );

      asyncdns_process();
}


/***************************************************************************
check if a particular name is already being queried
  ****************************************************************************/
static BOOL query_current(struct query_record *r)
{
      return dns_current &&
            nmb_name_equal(&r->name, 
                     &dns_current->packet.nmb.question.question_name);
}


/***************************************************************************
  write a query to the child process
  ****************************************************************************/
static BOOL write_child(struct packet_struct *p)
{
      struct query_record r;

      r.name = p->packet.nmb.question.question_name;

      return write_data(fd_out, (char *)&r, sizeof(r)) == sizeof(r);
}

/***************************************************************************
  check the DNS queue
  ****************************************************************************/
void run_dns_queue(void)
{
      struct query_record r;
      struct packet_struct *p, *p2;
      struct name_record *namerec;
      int size;

      if (fd_in == -1)
            return;

        /* Allow SIGTERM to kill us. */
        BlockSignals(False, SIGTERM);

      if (!process_exists(child_pid)) {
            close(fd_in);
            start_async_dns();
      }

      if ((size=read_data(fd_in, (char *)&r, sizeof(r))) != sizeof(r)) {
            if (size) {
                  DEBUG(0,("Incomplete DNS answer from child!\n"));
                  fd_in = -1;
            }
                BlockSignals(True, SIGTERM);
            return;
      }

        BlockSignals(True, SIGTERM);

      namerec = add_dns_result(&r.name, r.result);

      if (dns_current) {
            if (query_current(&r)) {
                  DEBUG(3,("DNS calling send_wins_name_query_response\n"));
                  in_dns = 1;
                        if(namerec == NULL)
                          send_wins_name_query_response(NAM_ERR, dns_current, NULL);
                        else
                    send_wins_name_query_response(0,dns_current,namerec);
                  in_dns = 0;
            }

            dns_current->locked = False;
            free_packet(dns_current);
            dns_current = NULL;
      }

      /* loop over the whole dns queue looking for entries that
         match the result we just got */
      for (p = dns_queue; p;) {
            struct nmb_packet *nmb = &p->packet.nmb;
            struct nmb_name *question = &nmb->question.question_name;

            if (nmb_name_equal(question, &r.name)) {
                  DEBUG(3,("DNS calling send_wins_name_query_response\n"));
                  in_dns = 1;
                        if(namerec == NULL)
                    send_wins_name_query_response(NAM_ERR, p, NULL);
                        else
                          send_wins_name_query_response(0,p,namerec);
                  in_dns = 0;
                  p->locked = False;

                  if (p->prev)
                        p->prev->next = p->next;
                  else
                        dns_queue = p->next;
                  if (p->next)
                        p->next->prev = p->prev;
                  p2 = p->next;
                  free_packet(p);
                  p = p2;
            } else {
                  p = p->next;
            }
      }

      if (dns_queue) {
            dns_current = dns_queue;
            dns_queue = dns_queue->next;
            if (dns_queue) dns_queue->prev = NULL;
            dns_current->next = NULL;

            if (!write_child(dns_current)) {
                  DEBUG(3,("failed to send DNS query to child!\n"));
                  return;
            }
      }

}

/***************************************************************************
queue a DNS query
  ****************************************************************************/
BOOL queue_dns_query(struct packet_struct *p,struct nmb_name *question,
                 struct name_record **n)
{
      if (in_dns || fd_in == -1)
            return False;

      if (!dns_current) {
            if (!write_child(p)) {
                  DEBUG(3,("failed to send DNS query to child!\n"));
                  return False;
            }
            dns_current = p;
            p->locked = True;
      } else {
            p->locked = True;
            p->next = dns_queue;
            p->prev = NULL;
            if (p->next)
                  p->next->prev = p;
            dns_queue = p;
      }

      DEBUG(3,("added DNS query for %s\n", nmb_namestr(question)));
      return True;
}

#else


/***************************************************************************
  we use this when we can't do async DNS lookups
  ****************************************************************************/
BOOL queue_dns_query(struct packet_struct *p,struct nmb_name *question,
                 struct name_record **n)
{
      char *qname = question->name;
      struct in_addr dns_ip;

      DEBUG(3,("DNS search for %s - ", nmb_namestr(question)));

        /* Unblock TERM signal so we can be killed in DNS lookup. */
        BlockSignals(False, SIGTERM);

      dns_ip.s_addr = interpret_addr(qname);

        /* Re-block TERM signal. */
        BlockSignals(True, SIGTERM);

      *n = add_dns_result(question, dns_ip);
        if(*n == NULL)
          send_wins_name_query_response(NAM_ERR, p, NULL);
        else
          send_wins_name_query_response(0, p, *n);
      return False;
}

/***************************************************************************
 With sync dns there is no child to kill on SIGTERM.
  ****************************************************************************/
void kill_async_dns_child(void)
{
  return;
}
#endif

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