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/*
Unix SMB/Netbios implementation.
Version 1.9.
Samba utility functions
Copyright (C) Andrew Tridgell 1992-1998
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"
/* -------------------------------------------------------------------------- **
* Discussion...
*
* This module implements WINS failover.
*
* Microsoft's WINS servers provide a feature called WINS replication,
* which synchronises the WINS name databases between two or more servers.
* This means that the two servers can be used interchangably (more or
* less). WINS replication is particularly useful if you are trying to
* synchronise the WINS namespace between servers in remote locations, or
* if your WINS servers tend to crash a lot.
*
* WINS failover allows the client to 'switch' to a different WINS server
* if the current WINS server mysteriously disappears. On Windows
* systems, this is typically represented as 'primary' and 'secondary'
* WINS servers.
*
* Failover only works if the WINS servers are synced. If they are not,
* then
* a) if the primary WINS server never fails the client will never 'see'
* the secondary (or tertiary or...) WINS server name space.
* b) if the primary *does* fail, the client will be entering an
* unfamiliar namespace. The client itself will not be registered in
* that namespace and any names which match names in the previous
* space will likely resolve to different host IP addresses.
*
* One key thing to remember regarding WINS failover is that Samba does
* not (yet) implement WINS replication. For those interested, sniff port
* 42 (TCP? UDP? ...dunno off hand) and see what two MS WINS servers do.
*
* At this stage, only failover is implemented. The next thing is to add
* support for multi-WINS server registration and query
* (multi-membership).
*
* Multi-membership is a little wierd. The idea is that the client can
* register itself with multiple non-replicated WINS servers, and query
* all of those servers (in a prescribed sequence) to resolve a name.
*
* The implications of multi-membership are not quite clear. Worth
* trying, I suppose. Changes will be needed in the name query and
* registration code to accomodate this feature. Also, there will need to
* be some sort of syntax extension for the 'wins server' parameter in
* smb.conf. I'm thinking that a colon could be used as a separator.
*
* Of course, for each WINS namespace there might be multiple, synced WINS
* servers. The change to this module would likely be the addition of a
* linked list of linked lists.
*
* crh@samba.org
*/
/* -------------------------------------------------------------------------- **
* Defines...
*
* NECROMANCYCLE - The dead server retry period, in seconds. When a WINS
* server is declared dead, wait this many seconds before
* attempting to communicate with it.
*/
#define NECROMANCYCLE 600 /* 600 seconds == 10 minutes. */
/* -------------------------------------------------------------------------- **
* Typedefs...
*/
typedef struct
{
ubi_slNode node; /* Linked list node structure. */
time_t mourning; /* If greater than current time server is dead, Jim. */
char *server; /* DNS name or IP of NBNS server to query. */
} list_entry;
/* -------------------------------------------------------------------------- **
* Private, static variables.
*/
static ubi_slNewList( wins_srv_list );
/* -------------------------------------------------------------------------- **
* Functions...
*/
BOOL wins_srv_load_list( char *src )
/* ------------------------------------------------------------------------ **
* Create or recreate the linked list of failover WINS servers.
*/
{
list_entry *entry;
char *p = src;
pstring wins_id_bufr;
unsigned long count;
/* Empty the list. */
while( NULL != (entry =(list_entry *)ubi_slRemHead( wins_srv_list )) )
{
if( entry->server )
free( entry->server );
free( entry );
}
(void)ubi_slInitList( wins_srv_list ); /* shouldn't be needed */
/* Parse out the DNS names or IP addresses of the WINS servers. */
DEBUG( 4, ("wins_srv: Building WINS server list:\n") );
while( next_token( &p, wins_id_bufr, LIST_SEP, sizeof( wins_id_bufr ) ) )
{
entry = (list_entry *)malloc( sizeof( list_entry ) );
if( NULL == entry )
{
DEBUG( 0, ("wins_srv_load_list(): malloc(list_entry) failed.\n") );
}
else
{
entry->mourning = 0;
if( NULL == (entry->server = strdup( wins_id_bufr )) )
{
free( entry );
DEBUG( 0, ("wins_srv_load_list(): strdup(\"%s\") failed.\n", wins_id_bufr) );
}
else
{
/* Add server to list. */
(void)ubi_slAddTail( wins_srv_list, entry );
DEBUGADD( 4, ("\t\t%s,\n", wins_id_bufr) );
}
}
}
count = ubi_slCount( wins_srv_list );
DEBUGADD( 4, ( "\t\t%d WINS server%s listed.\n", count, (1==count)?"":"s" ) );
return( (count > 0) ? True : False );
} /* wins_srv_load_list */
char *wins_srv( void )
/* ------------------------------------------------------------------------ **
*/
{
time_t now = time(NULL);
list_entry *entry = (list_entry *)ubi_slFirst( wins_srv_list );
list_entry *coldest = entry;
/* Go through the list. Look for the first live entry. */
while( (NULL != entry) && (now < entry->mourning) )
{
entry = (list_entry *)ubi_slNext( entry );
if( entry->mourning < coldest->mourning )
coldest = entry;
}
/* If they were all dead, then return the one that's been dead longest. */
if( NULL == entry )
{
entry = coldest;
DEBUG( 4, ("wins_srv: All WINS servers appear to have failed.\n") );
}
/* The list could be empty. Check it. */
if( NULL == entry )
return( NULL );
return( entry->server );
} /* wins_srv */
void wins_srv_died( char *boothill )
/* ------------------------------------------------------------------------ **
* Called to indicate that a specific WINS server has died.
*/
{
list_entry *entry = (list_entry *)ubi_slFirst( wins_srv_list );
while( NULL != entry )
{
/* Match based on server ID [DNS name or IP]. */
if( 0 == strcmp( boothill, entry->server ) )
{
entry->mourning = time(NULL) + NECROMANCYCLE;
DEBUG( 2, ("wins_srv: WINS server %s appears to be down.\n", boothill) );
return;
}
entry = (list_entry *)ubi_slNext( entry );
}
} /* wins_srv_died */
unsigned long wins_srv_count( void )
/* ------------------------------------------------------------------------ **
* Return the total number of entries in the list, dead or alive.
*/
{
return( ubi_slCount( wins_srv_list ) );
} /* wins_srv_count */
/* ========================================================================== */
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