res_state.c revision 68c2755d71750401d82d9aa17774ebd385cb5dc0 
1/*
2 * Copyright (C) 2008 The Android Open Source Project
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 *  * Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 *  * Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in
12 *    the documentation and/or other materials provided with the
13 *    distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
16 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
17 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
18 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
19 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
21 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
22 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
23 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
24 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
25 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 */
28#include <sys/cdefs.h>
29#include <sys/types.h>
30#include <arpa/inet.h>
31#include <arpa/nameser.h>
32#include <netdb.h>
33#include "resolv_private.h"
34#include "resolv_cache.h"
35#include <pthread.h>
36#include <stdlib.h>
37
38#define _REALLY_INCLUDE_SYS__SYSTEM_PROPERTIES_H_
39#include <sys/_system_properties.h>
40
41/* Set to 1 to enable debug traces */
42#define DEBUG 0
43
44#if DEBUG
45#  include "private/libc_logging.h"
46#  include <unistd.h>  /* for gettid() */
47#  define D(...) __libc_format_log(ANDROID_LOG_DEBUG,"libc", __VA_ARGS__)
48#else
49#  define D(...)  do{}while(0)
50#endif
51
52static pthread_key_t   _res_key;
53static pthread_once_t  _res_once = PTHREAD_ONCE_INIT;
54
55typedef struct {
56    int                  _h_errno;
57    // TODO: Have one __res_state per network so we don't have to repopulate frequently.
58    struct __res_state  _nres[1];
59    unsigned             _serial;
60    struct prop_info*   _pi;
61    struct res_static   _rstatic[1];
62} _res_thread;
63
64static _res_thread*
65_res_thread_alloc(void)
66{
67    _res_thread*  rt = calloc(1, sizeof(*rt));
68
69    if (rt) {
70        rt->_h_errno = 0;
71        /* Special system property which tracks any changes to 'net.*'. */
72        rt->_serial = 0;
73        rt->_pi = (struct prop_info*) __system_property_find("net.change");
74        if (rt->_pi) {
75            rt->_serial = __system_property_serial(rt->_pi);
76        }
77        memset(rt->_rstatic, 0, sizeof rt->_rstatic);
78    }
79    return rt;
80}
81
82static void
83_res_static_done( res_static  rs )
84{
85    /* fortunately, there is nothing to do here, since the
86     * points in h_addr_ptrs and host_aliases should all
87     * point to 'hostbuf'
88     */
89    if (rs->hostf) {  /* should not happen in theory, but just be safe */
90        fclose(rs->hostf);
91        rs->hostf = NULL;
92    }
93    free(rs->servent.s_aliases);
94}
95
96static void
97_res_thread_free( void*  _rt )
98{
99    _res_thread*  rt = _rt;
100
101    D("%s: rt=%p for thread=%d", __FUNCTION__, rt, gettid());
102
103    _res_static_done(rt->_rstatic);
104    res_ndestroy(rt->_nres);
105    free(rt);
106}
107
108static void
109_res_init_key( void )
110{
111    pthread_key_create( &_res_key, _res_thread_free );
112}
113
114static _res_thread*
115_res_thread_get(void)
116{
117    _res_thread*  rt;
118    pthread_once( &_res_once, _res_init_key );
119    rt = pthread_getspecific( _res_key );
120
121    if (rt != NULL) {
122        /* We already have one thread-specific DNS state object.
123         * Check the serial value for any changes to net.* properties */
124        D("%s: Called for tid=%d rt=%p rt->pi=%p rt->serial=%d",
125           __FUNCTION__, gettid(), rt, rt->_pi, rt->_serial);
126        if (rt->_pi == NULL) {
127            /* The property wasn't created when _res_thread_get() was
128             * called the last time. This should only happen very
129             * early during the boot sequence. First, let's try to see if it
130             * is here now. */
131            rt->_pi = (struct prop_info*) __system_property_find("net.change");
132            if (rt->_pi == NULL) {
133                /* Still nothing, return current state */
134                D("%s: exiting for tid=%d rt=%d since system property not found",
135                  __FUNCTION__, gettid(), rt);
136                return rt;
137            }
138        }
139        if (rt->_serial == __system_property_serial(rt->_pi)) {
140            /* Nothing changed, so return the current state */
141            D("%s: tid=%d rt=%p nothing changed, returning",
142              __FUNCTION__, gettid(), rt);
143            return rt;
144        }
145        /* Update the recorded serial number, and go reset the state */
146        rt->_serial = __system_property_serial(rt->_pi);
147        goto RESET_STATE;
148    }
149
150    /* It is the first time this function is called in this thread,
151     * we need to create a new thread-specific DNS resolver state. */
152    rt = _res_thread_alloc();
153    if (rt == NULL) {
154        return NULL;
155    }
156    pthread_setspecific( _res_key, rt );
157    D("%s: tid=%d Created new DNS state rt=%p",
158      __FUNCTION__, gettid(), rt);
159
160RESET_STATE:
161    /* Reset the state, note that res_ninit() can now properly reset
162     * an existing state without leaking memory.
163     */
164    D("%s: tid=%d, rt=%p, resetting DNS state (options RES_INIT=%d)",
165      __FUNCTION__, gettid(), rt, (rt->_nres->options & RES_INIT) != 0);
166    if ( res_ninit( rt->_nres ) < 0 ) {
167        /* This should not happen */
168        D("%s: tid=%d rt=%p, woot, res_ninit() returned < 0",
169          __FUNCTION__, gettid(), rt);
170        _res_thread_free(rt);
171        pthread_setspecific( _res_key, NULL );
172        return NULL;
173    }
174    return rt;
175}
176
177__LIBC_HIDDEN__
178struct __res_state _nres;
179
180#if 0
181struct resolv_cache*
182__get_res_cache(void)
183{
184    _res_thread*  rt = _res_thread_get();
185
186    if (!rt)
187        return NULL;
188
189    if (!rt->_cache) {
190        rt->_cache = _resolv_cache_create();
191    }
192    return rt->_cache;
193}
194#endif
195
196int*
197__get_h_errno(void)
198{
199    _res_thread*  rt    = _res_thread_get();
200    static int    panic = NETDB_INTERNAL;
201
202    return rt ? &rt->_h_errno : &panic;
203}
204
205res_state
206__res_get_state(void)
207{
208    _res_thread*  rt = _res_thread_get();
209
210    return rt ? rt->_nres : NULL;
211}
212
213void
214__res_put_state(res_state res __unused)
215{
216    /* nothing to do */
217}
218
219res_static
220__res_get_static(void)
221{
222    _res_thread*  rt = _res_thread_get();
223
224    return rt ? rt->_rstatic : NULL;
225}
226