source: branches/samba-3.3.x/source/nmbd/asyncdns.c

/*
   Unix SMB/CIFS 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 3 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/>.
   */
#ifdef __OS2__
#define pipe(A) os2_pipe(A)
#endif

#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;
        unstring qname;

        pull_ascii_nstring(qname, sizeof(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));
                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)));

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

        return find_name_on_subnet(wins_server_subnet, question, FIND_ANY_NAME);
}

#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;
        unstring qname;

        DEBUGLEVEL = -1;

        while (1) {
                NTSTATUS status;

                status = read_data(fd_in, (char *)&r, sizeof(r));

                if (!NT_STATUS_IS_OK(status)) {
                        break;
                }

                pull_ascii_nstring( qname, sizeof(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) {
                kill(child_pid, SIGTERM);
                child_pid = -1;
        }
}

/***************************************************************************
  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 );

        if (!reinit_after_fork(nmbd_messaging_context(),
                               nmbd_event_context(), true)) {
                DEBUG(0,("reinit_after_fork() failed\n"));
                smb_panic("reinit_after_fork() failed");
        }

        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;
        NTSTATUS status;

        if (fd_in == -1)
                return;

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

        if (!process_exists_by_pid(child_pid)) {
                close(fd_in);
                close(fd_out);
                start_async_dns();
        }

        status = read_data(fd_in, (char *)&r, sizeof(r));

        if (!NT_STATUS_IS_OK(status)) {
                DEBUG(0, ("read from child failed: %s\n", nt_errstr(status)));
                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)
{
        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 *namerec = NULL;
        struct in_addr dns_ip;
        unstring qname;

        pull_ascii_nstring(qname, sizeof(qname), question->name);

        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);

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

/***************************************************************************
 With sync dns there is no child to kill on SIGTERM.
  ****************************************************************************/

void kill_async_dns_child(void)
{
        return;
}
#endif