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Add support for deleting per-network DNS resolver caches.

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This is required when the possible range of NetIds is large to
prevent netd consuming excessive amounts of memory.
This required replacing the per-cache locks in favor of a single
global lock to prevent accesses to deleted caches.

Change-Id: I99d058bafea5de743e56075dbed74031da4df63f
This commit is contained in:
Paul Jensen 2014-04-08 15:43:41 -04:00 committed by Lorenzo Colitti
parent 7fbc7481cc
commit 41d9a50371
4 changed files with 100 additions and 73 deletions
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11
libc/dns/include/resolv_cache.h
View File

@ -32,11 +32,6 @@
#include <sys/cdefs.h>
struct __res_state;
struct resolv_cache; /* forward */
/* Gets the cache for a network. Returned cache might be NULL. */
__LIBC_HIDDEN__
extern struct resolv_cache* __get_res_cache(unsigned netid);
/* sets the name server addresses to the provided res_state structure. The
* name servers are retrieved from the cache which is associated
@ -53,7 +48,7 @@ typedef enum {
__LIBC_HIDDEN__
extern ResolvCacheStatus
_resolv_cache_lookup( struct resolv_cache* cache,
_resolv_cache_lookup( unsigned netid,
const void* query,
int querylen,
void* answer,
@ -65,7 +60,7 @@ _resolv_cache_lookup( struct resolv_cache* cache,
*/
__LIBC_HIDDEN__
extern void
_resolv_cache_add( struct resolv_cache* cache,
_resolv_cache_add( unsigned netid,
const void* query,
int querylen,
const void* answer,
@ -74,7 +69,7 @@ _resolv_cache_add( struct resolv_cache* cache,
/* Notify the cache a request failed */
__LIBC_HIDDEN__
extern void
_resolv_cache_query_failed( struct resolv_cache* cache,
_resolv_cache_query_failed( unsigned netid,
const void* query,
int querylen);

3
libc/dns/include/resolv_netid.h
View File

@ -65,6 +65,9 @@ extern void _resolv_set_nameservers_for_net(unsigned netid,
/* flush the cache associated with a certain network */
extern void _resolv_flush_cache_for_net(unsigned netid);
/* delete the cache associated with a certain network */
extern void _resolv_delete_cache_for_net(unsigned netid);
__END_DECLS
#endif /* _RESOLV_NETID_H */

128
libc/dns/resolv/res_cache.c
View File

@ -1218,7 +1218,6 @@ typedef struct resolv_cache {
int max_entries;
int num_entries;
Entry mru_list;
pthread_mutex_t lock;
int last_id;
Entry* entries;
PendingReqInfo pending_requests;
@ -1236,6 +1235,15 @@ struct resolv_cache_info {
#define HTABLE_VALID(x) ((x) != NULL && (x) != HTABLE_DELETED)
static pthread_once_t _res_cache_once = PTHREAD_ONCE_INIT;
static void _res_cache_init(void);
// lock protecting everything in the _resolve_cache_info structs (next ptr, etc)
static pthread_mutex_t _res_cache_list_lock;
/* gets cache associated with a network, or NULL if none exists */
static struct resolv_cache* _find_named_cache_locked(unsigned netid);
static void
_cache_flush_pending_requests_locked( struct resolv_cache* cache )
{
@ -1256,18 +1264,18 @@ _cache_flush_pending_requests_locked( struct resolv_cache* cache )
}
}
/* return 0 if no pending request is found matching the key
* if a matching request is found the calling thread will wait
* and return 1 when released */
/* Return 0 if no pending request is found matching the key.
* If a matching request is found the calling thread will wait until
* the matching request completes, then update *cache and return 1. */
static int
_cache_check_pending_request_locked( struct resolv_cache* cache, Entry* key )
_cache_check_pending_request_locked( struct resolv_cache** cache, Entry* key, unsigned netid )
{
struct pending_req_info *ri, *prev;
int exist = 0;
if (cache && key) {
ri = cache->pending_requests.next;
prev = &cache->pending_requests;
if (*cache && key) {
ri = (*cache)->pending_requests.next;
prev = &(*cache)->pending_requests;
while (ri) {
if (ri->hash == key->hash) {
exist = 1;
@ -1288,7 +1296,9 @@ _cache_check_pending_request_locked( struct resolv_cache* cache, Entry* key )
struct timespec ts = {0,0};
XLOG("Waiting for previous request");
ts.tv_sec = _time_now() + PENDING_REQUEST_TIMEOUT;
pthread_cond_timedwait(&ri->cond, &cache->lock, &ts);
pthread_cond_timedwait(&ri->cond, &_res_cache_list_lock, &ts);
/* Must update *cache as it could have been deleted. */
*cache = _find_named_cache_locked(netid);
}
}
@ -1325,17 +1335,25 @@ _cache_notify_waiting_tid_locked( struct resolv_cache* cache, Entry* key )
/* notify the cache that the query failed */
void
_resolv_cache_query_failed( struct resolv_cache* cache,
_resolv_cache_query_failed( unsigned netid,
const void* query,
int querylen)
{
Entry key[1];
Cache* cache;
if (cache && entry_init_key(key, query, querylen)) {
pthread_mutex_lock(&cache->lock);
if (!entry_init_key(key, query, querylen))
return;
pthread_mutex_lock(&_res_cache_list_lock);
cache = _find_named_cache_locked(netid);
if (cache) {
_cache_notify_waiting_tid_locked(cache, key);
pthread_mutex_unlock(&cache->lock);
}
pthread_mutex_unlock(&_res_cache_list_lock);
}
static void
@ -1391,7 +1409,6 @@ _resolv_cache_create( void )
cache->max_entries = _res_cache_get_max_entries();
cache->entries = calloc(sizeof(*cache->entries), cache->max_entries);
if (cache->entries) {
pthread_mutex_init( &cache->lock, NULL );
cache->mru_list.mru_prev = cache->mru_list.mru_next = &cache->mru_list;
XLOG("%s: cache created\n", __FUNCTION__);
} else {
@ -1586,7 +1603,7 @@ static void _cache_remove_expired(Cache* cache) {
}
ResolvCacheStatus
_resolv_cache_lookup( struct resolv_cache* cache,
_resolv_cache_lookup( unsigned netid,
const void* query,
int querylen,
void* answer,
@ -1597,6 +1614,7 @@ _resolv_cache_lookup( struct resolv_cache* cache,
Entry** lookup;
Entry* e;
time_t now;
Cache* cache;
ResolvCacheStatus result = RESOLV_CACHE_NOTFOUND;
@ -1609,7 +1627,14 @@ _resolv_cache_lookup( struct resolv_cache* cache,
return RESOLV_CACHE_UNSUPPORTED;
}
/* lookup cache */
pthread_mutex_lock( &cache->lock );
pthread_once(&_res_cache_once, _res_cache_init);
pthread_mutex_lock(&_res_cache_list_lock);
cache = _find_named_cache_locked(netid);
if (cache == NULL) {
result = RESOLV_CACHE_UNSUPPORTED;
goto Exit;
}
/* see the description of _lookup_p to understand this.
* the function always return a non-NULL pointer.
@ -1621,7 +1646,7 @@ _resolv_cache_lookup( struct resolv_cache* cache,
XLOG( "NOT IN CACHE");
// calling thread will wait if an outstanding request is found
// that matching this query
if (!_cache_check_pending_request_locked(cache, key)) {
if (!_cache_check_pending_request_locked(&cache, key, netid) || cache == NULL) {
goto Exit;
} else {
lookup = _cache_lookup_p(cache, key);
@ -1662,13 +1687,13 @@ _resolv_cache_lookup( struct resolv_cache* cache,
result = RESOLV_CACHE_FOUND;
Exit:
pthread_mutex_unlock( &cache->lock );
pthread_mutex_unlock(&_res_cache_list_lock);
return result;
}
void
_resolv_cache_add( struct resolv_cache* cache,
_resolv_cache_add( unsigned netid,
const void* query,
int querylen,
const void* answer,
@ -1678,6 +1703,7 @@ _resolv_cache_add( struct resolv_cache* cache,
Entry* e;
Entry** lookup;
u_long ttl;
Cache* cache = NULL;
/* don't assume that the query has already been cached
*/
@ -1686,7 +1712,12 @@ _resolv_cache_add( struct resolv_cache* cache,
return;
}
pthread_mutex_lock( &cache->lock );
pthread_mutex_lock(&_res_cache_list_lock);
cache = _find_named_cache_locked(netid);
if (cache == NULL) {
goto Exit;
}
XLOG( "%s: query:", __FUNCTION__ );
XLOG_QUERY(query,querylen);
@ -1732,8 +1763,10 @@ _resolv_cache_add( struct resolv_cache* cache,
_cache_dump_mru(cache);
#endif
Exit:
_cache_notify_waiting_tid_locked(cache, key);
pthread_mutex_unlock( &cache->lock );
if (cache != NULL) {
_cache_notify_waiting_tid_locked(cache, key);
}
pthread_mutex_unlock(&_res_cache_list_lock);
}
/****************************************************************************/
@ -1744,20 +1777,13 @@ Exit:
/****************************************************************************/
/****************************************************************************/
static pthread_once_t _res_cache_once = PTHREAD_ONCE_INIT;
// Head of the list of caches. Protected by _res_cache_list_lock.
static struct resolv_cache_info _res_cache_list;
// lock protecting everything in the _resolve_cache_info structs (next ptr, etc)
static pthread_mutex_t _res_cache_list_lock;
/* insert resolv_cache_info into the list of resolv_cache_infos */
static void _insert_cache_info_locked(struct resolv_cache_info* cache_info);
/* creates a resolv_cache_info */
static struct resolv_cache_info* _create_cache_info( void );
/* gets cache associated with a network, or NULL if none exists */
static struct resolv_cache* _find_named_cache_locked(unsigned netid);
/* gets a resolv_cache_info associated with a network, or NULL if not found */
static struct resolv_cache_info* _find_cache_info_locked(unsigned netid);
/* look up the named cache, and creates one if needed */
@ -1785,22 +1811,6 @@ _res_cache_init(void)
pthread_mutex_init(&_res_cache_list_lock, NULL);
}
struct resolv_cache*
__get_res_cache(unsigned netid)
{
struct resolv_cache *cache;
pthread_once(&_res_cache_once, _res_cache_init);
pthread_mutex_lock(&_res_cache_list_lock);
/* Does NOT create a cache if it does not exist. */
cache = _find_named_cache_locked(netid);
pthread_mutex_unlock(&_res_cache_list_lock);
XLOG("%s: netid=%u, cache=%p\n", __FUNCTION__, netid, cache);
return cache;
}
static struct resolv_cache*
_get_res_cache_for_net_locked(unsigned netid)
{
@ -1837,12 +1847,36 @@ _flush_cache_for_net_locked(unsigned netid)
{
struct resolv_cache* cache = _find_named_cache_locked(netid);
if (cache) {
pthread_mutex_lock(&cache->lock);
_cache_flush_locked(cache);
pthread_mutex_unlock(&cache->lock);
}
}
void _resolv_delete_cache_for_net(unsigned netid)
{
pthread_once(&_res_cache_once, _res_cache_init);
pthread_mutex_lock(&_res_cache_list_lock);
struct resolv_cache_info* prev_cache_info = &_res_cache_list;
while (prev_cache_info->next) {
struct resolv_cache_info* cache_info = prev_cache_info->next;
if (cache_info->netid == netid) {
prev_cache_info->next = cache_info->next;
_cache_flush_locked(cache_info->cache);
free(cache_info->cache->entries);
free(cache_info->cache);
_free_nameservers_locked(cache_info);
free(cache_info);
break;
}
prev_cache_info = prev_cache_info->next;
}
pthread_mutex_unlock(&_res_cache_list_lock);
}
static struct resolv_cache_info*
_create_cache_info(void)
{

31
libc/dns/resolv/res_send.c
View File

@ -367,7 +367,6 @@ res_nsend(res_state statp,
int gotsomewhere, terrno, try, v_circuit, resplen, ns, n;
char abuf[NI_MAXHOST];
#if USE_RESOLV_CACHE
struct resolv_cache* cache;
ResolvCacheStatus cache_status = RESOLV_CACHE_UNSUPPORTED;
#endif
@ -389,21 +388,17 @@ res_nsend(res_state statp,
terrno = ETIMEDOUT;
#if USE_RESOLV_CACHE
// get the cache associated with the network
cache = __get_res_cache(statp->netid);
if (cache != NULL) {
int anslen = 0;
cache_status = _resolv_cache_lookup(
cache, buf, buflen,
ans, anssiz, &anslen);
int anslen = 0;
cache_status = _resolv_cache_lookup(
statp->netid, buf, buflen,
ans, anssiz, &anslen);
if (cache_status == RESOLV_CACHE_FOUND) {
return anslen;
} else {
// had a cache miss for a known network, so populate the thread private
// data so the normal resolve path can do its thing
_resolv_populate_res_for_net(statp);
}
if (cache_status == RESOLV_CACHE_FOUND) {
return anslen;
} else if (cache_status != RESOLV_CACHE_UNSUPPORTED) {
// had a cache miss for a known network, so populate the thread private
// data so the normal resolve path can do its thing
_resolv_populate_res_for_net(statp);
}
if (statp->nscount == 0) {
@ -602,7 +597,7 @@ res_nsend(res_state statp,
#if USE_RESOLV_CACHE
if (cache_status == RESOLV_CACHE_NOTFOUND) {
_resolv_cache_add(cache, buf, buflen,
_resolv_cache_add(statp->netid, buf, buflen,
ans, resplen);
}
#endif
@ -658,13 +653,13 @@ res_nsend(res_state statp,
errno = terrno;
#if USE_RESOLV_CACHE
_resolv_cache_query_failed(cache, buf, buflen);
_resolv_cache_query_failed(statp->netid, buf, buflen);
#endif
return (-1);
fail:
#if USE_RESOLV_CACHE
_resolv_cache_query_failed(cache, buf, buflen);
_resolv_cache_query_failed(statp->netid, buf, buflen);
#endif
res_nclose(statp);
return (-1);