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r22714: Prevent DNS lookup storms when the DNS servers are unreachable.

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Helps when transitioning from offline to online mode.

Note that this is a quick hack and a better solution
would be to start the DNS server's state between processes
(similar to the namecache entries).
This commit is contained in:
Gerald Carter 2007-05-06 21:06:55 +00:00 committed by Gerald (Jerry) Carter
parent 4086ef15b3
commit 4f05c6fe26
1 changed files with 40 additions and 9 deletions
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49
source/libads/dns.c
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@ -270,45 +270,76 @@ static int dnssrvcmp( struct dns_rr_srv *a, struct dns_rr_srv *b )
Simple wrapper for a DNS query Simple wrapper for a DNS query
*********************************************************************/ *********************************************************************/
#define DNS_FAILED_WAITTIME 30
static NTSTATUS dns_send_req( TALLOC_CTX *ctx, const char *name, int q_type, static NTSTATUS dns_send_req( TALLOC_CTX *ctx, const char *name, int q_type,
uint8 **buf, int *resp_length ) uint8 **buf, int *resp_length )
{ {
uint8 *buffer = NULL; uint8 *buffer = NULL;
size_t buf_len; size_t buf_len;
int resp_len = NS_PACKETSZ; int resp_len = NS_PACKETSZ;
static time_t last_dns_check = 0;
static NTSTATUS last_dns_status = NT_STATUS_OK;
time_t now = time(NULL);
/* Try to prevent bursts of DNS lookups if the server is down */
/* Protect against large clock changes */
if ( last_dns_check > now )
last_dns_check = 0;
/* IF we had a DNS timeout or a bad server and we are still
in the 30 second cache window, just return the previous
status and save the network timeout. */
if ( (NT_STATUS_EQUAL(last_dns_status,NT_STATUS_IO_TIMEOUT) ||
NT_STATUS_EQUAL(last_dns_status,NT_STATUS_CONNECTION_REFUSED)) &&
(last_dns_check+DNS_FAILED_WAITTIME) > now )
{
DEBUG(10,("last_dns_check: Returning cached status (%s)\n",
nt_errstr(last_dns_status) ));
return last_dns_status;
}
/* Send the Query */
do { do {
if ( buffer ) if ( buffer )
TALLOC_FREE( buffer ); TALLOC_FREE( buffer );
buf_len = resp_len * sizeof(uint8); buf_len = resp_len * sizeof(uint8);
if (buf_len) { if (buf_len) {
if ( (buffer = TALLOC_ARRAY(ctx, uint8, buf_len)) == NULL ) { if ( (buffer = TALLOC_ARRAY(ctx, uint8, buf_len)) == NULL ) {
DEBUG(0,("ads_dns_lookup_srv: talloc() failed!\n")); DEBUG(0,("ads_dns_lookup_srv: talloc() failed!\n"));
return NT_STATUS_NO_MEMORY; last_dns_status = NT_STATUS_NO_MEMORY;
last_dns_check = time(NULL);
return last_dns_status;
} }
} else {
buffer = NULL;
} }
if ( (resp_len = res_query(name, C_IN, q_type, buffer, buf_len)) < 0 ) { if ( (resp_len = res_query(name, C_IN, q_type, buffer, buf_len)) < 0 ) {
DEBUG(3,("ads_dns_lookup_srv: Failed to resolve %s (%s)\n", name, strerror(errno))); DEBUG(3,("ads_dns_lookup_srv: Failed to resolve %s (%s)\n", name, strerror(errno)));
TALLOC_FREE( buffer ); TALLOC_FREE( buffer );
last_dns_status = NT_STATUS_UNSUCCESSFUL;
if (errno == ETIMEDOUT) { if (errno == ETIMEDOUT) {
return NT_STATUS_IO_TIMEOUT; last_dns_status = NT_STATUS_IO_TIMEOUT;
} }
if (errno == ECONNREFUSED) { if (errno == ECONNREFUSED) {
return NT_STATUS_CONNECTION_REFUSED; last_dns_status = NT_STATUS_CONNECTION_REFUSED;
} }
return NT_STATUS_UNSUCCESSFUL; last_dns_check = time(NULL);
return last_dns_status;
} }
} while ( buf_len < resp_len && resp_len < MAX_DNS_PACKET_SIZE ); } while ( buf_len < resp_len && resp_len < MAX_DNS_PACKET_SIZE );
*buf = buffer; *buf = buffer;
*resp_length = resp_len; *resp_length = resp_len;
return NT_STATUS_OK; last_dns_check = time(NULL);
last_dns_status = NT_STATUS_OK;
return last_dns_status;
} }
/********************************************************************* /*********************************************************************