1/* Copyright (C) 2004-2019 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3 Contribute by Ulrich Drepper <drepper@redhat.com>, 2004.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <http://www.gnu.org/licenses/>. */
18
19#include <assert.h>
20#include <errno.h>
21#include <fcntl.h>
22#include <mqueue.h>
23#include <pthread.h>
24#include <signal.h>
25#include <stdlib.h>
26#include <string.h>
27#include <sysdep.h>
28#include <unistd.h>
29#include <sys/socket.h>
30#include <not-cancel.h>
31#include <nptl/pthreadP.h>
32
33
34#ifdef __NR_mq_notify
35
36/* Defined in the kernel headers: */
37#define NOTIFY_COOKIE_LEN 32 /* Length of the cookie used. */
38#define NOTIFY_WOKENUP 1 /* Code for notifcation. */
39#define NOTIFY_REMOVED 2 /* Code for closed message queue
40 of de-notifcation. */
41
42
43/* Data structure for the queued notification requests. */
44union notify_data
45{
46 struct
47 {
48 void (*fct) (union sigval); /* The function to run. */
49 union sigval param; /* The parameter to pass. */
50 pthread_attr_t *attr; /* Attributes to create the thread with. */
51 /* NB: on 64-bit machines the struct as a size of 24 bytes. Which means
52 byte 31 can still be used for returning the status. */
53 };
54 char raw[NOTIFY_COOKIE_LEN];
55};
56
57
58/* Keep track of the initialization. */
59static pthread_once_t once = PTHREAD_ONCE_INIT;
60
61
62/* The netlink socket. */
63static int netlink_socket = -1;
64
65
66/* Barrier used to make sure data passed to the new thread is not
67 resused by the parent. */
68static pthread_barrier_t notify_barrier;
69
70
71/* Modify the signal mask. We move this into a separate function so
72 that the stack space needed for sigset_t is not deducted from what
73 the thread can use. */
74static int
75__attribute__ ((noinline))
76change_sigmask (int how, sigset_t *oss)
77{
78 sigset_t ss;
79 sigfillset (&ss);
80 return pthread_sigmask (how, &ss, oss);
81}
82
83
84/* The function used for the notification. */
85static void *
86notification_function (void *arg)
87{
88 /* Copy the function and parameter so that the parent thread can go
89 on with its life. */
90 volatile union notify_data *data = (volatile union notify_data *) arg;
91 void (*fct) (union sigval) = data->fct;
92 union sigval param = data->param;
93
94 /* Let the parent go. */
95 (void) __pthread_barrier_wait (&notify_barrier);
96
97 /* Make the thread detached. */
98 (void) pthread_detach (pthread_self ());
99
100 /* The parent thread has all signals blocked. This is probably a
101 bit surprising for this thread. So we unblock all of them. */
102 (void) change_sigmask (SIG_UNBLOCK, NULL);
103
104 /* Now run the user code. */
105 fct (param);
106
107 /* And we are done. */
108 return NULL;
109}
110
111
112/* Helper thread. */
113static void *
114helper_thread (void *arg)
115{
116 while (1)
117 {
118 union notify_data data;
119
120 ssize_t n = __recv (netlink_socket, &data, sizeof (data),
121 MSG_NOSIGNAL | MSG_WAITALL);
122 if (n < NOTIFY_COOKIE_LEN)
123 continue;
124
125 if (data.raw[NOTIFY_COOKIE_LEN - 1] == NOTIFY_WOKENUP)
126 {
127 /* Just create the thread as instructed. There is no way to
128 report a problem with creating a thread. */
129 pthread_t th;
130 if (__builtin_expect (pthread_create (&th, data.attr,
131 notification_function, &data)
132 == 0, 0))
133 /* Since we passed a pointer to DATA to the new thread we have
134 to wait until it is done with it. */
135 (void) __pthread_barrier_wait (&notify_barrier);
136 }
137 else if (data.raw[NOTIFY_COOKIE_LEN - 1] == NOTIFY_REMOVED)
138 /* The only state we keep is the copy of the thread attributes. */
139 free (data.attr);
140 }
141 return NULL;
142}
143
144
145static void
146reset_once (void)
147{
148 once = PTHREAD_ONCE_INIT;
149}
150
151
152static void
153init_mq_netlink (void)
154{
155 /* This code might be called a second time after fork(). The file
156 descriptor is inherited from the parent. */
157 if (netlink_socket == -1)
158 {
159 /* Just a normal netlink socket, not bound. */
160 netlink_socket = __socket (AF_NETLINK, SOCK_RAW | SOCK_CLOEXEC, 0);
161 /* No need to do more if we have no socket. */
162 if (netlink_socket == -1)
163 return;
164 }
165
166 int err = 1;
167
168 /* Initialize the barrier. */
169 if (__builtin_expect (__pthread_barrier_init (&notify_barrier, NULL, 2) == 0,
170 0))
171 {
172 /* Create the helper thread. */
173 pthread_attr_t attr;
174 (void) pthread_attr_init (&attr);
175 (void) pthread_attr_setdetachstate (&attr, PTHREAD_CREATE_DETACHED);
176 /* We do not need much stack space, the bare minimum will be enough. */
177 (void) pthread_attr_setstacksize (&attr, __pthread_get_minstack (&attr));
178
179 /* Temporarily block all signals so that the newly created
180 thread inherits the mask. */
181 sigset_t oss;
182 int have_no_oss = change_sigmask (SIG_BLOCK, &oss);
183
184 pthread_t th;
185 err = pthread_create (&th, &attr, helper_thread, NULL);
186
187 /* Reset the signal mask. */
188 if (!have_no_oss)
189 pthread_sigmask (SIG_SETMASK, &oss, NULL);
190
191 (void) pthread_attr_destroy (&attr);
192
193 if (err == 0)
194 {
195 static int added_atfork;
196
197 if (added_atfork == 0
198 && pthread_atfork (NULL, NULL, reset_once) != 0)
199 {
200 /* The child thread will call recv() which is a
201 cancellation point. */
202 (void) pthread_cancel (th);
203 err = 1;
204 }
205 else
206 added_atfork = 1;
207 }
208 }
209
210 if (err != 0)
211 {
212 __close_nocancel_nostatus (netlink_socket);
213 netlink_socket = -1;
214 }
215}
216
217
218/* Register notification upon message arrival to an empty message queue
219 MQDES. */
220int
221mq_notify (mqd_t mqdes, const struct sigevent *notification)
222{
223 /* Make sure the type is correctly defined. */
224 assert (sizeof (union notify_data) == NOTIFY_COOKIE_LEN);
225
226 /* Special treatment needed for SIGEV_THREAD. */
227 if (notification == NULL || notification->sigev_notify != SIGEV_THREAD)
228 return INLINE_SYSCALL (mq_notify, 2, mqdes, notification);
229
230 /* The kernel cannot directly start threads. This will have to be
231 done at userlevel. Since we cannot start threads from signal
232 handlers we have to create a dedicated thread which waits for
233 notifications for arriving messages and creates threads in
234 response. */
235
236 /* Initialize only once. */
237 pthread_once (&once, init_mq_netlink);
238
239 /* If we cannot create the netlink socket we cannot provide
240 SIGEV_THREAD support. */
241 if (__glibc_unlikely (netlink_socket == -1))
242 {
243 __set_errno (ENOSYS);
244 return -1;
245 }
246
247 /* Create the cookie. It will hold almost all the state. */
248 union notify_data data;
249 memset (&data, '\0', sizeof (data));
250 data.fct = notification->sigev_notify_function;
251 data.param = notification->sigev_value;
252
253 if (notification->sigev_notify_attributes != NULL)
254 {
255 /* The thread attribute has to be allocated separately. */
256 data.attr = (pthread_attr_t *) malloc (sizeof (pthread_attr_t));
257 if (data.attr == NULL)
258 return -1;
259
260 memcpy (data.attr, notification->sigev_notify_attributes,
261 sizeof (pthread_attr_t));
262 }
263
264 /* Construct the new request. */
265 struct sigevent se;
266 se.sigev_notify = SIGEV_THREAD;
267 se.sigev_signo = netlink_socket;
268 se.sigev_value.sival_ptr = &data;
269
270 /* Tell the kernel. */
271 int retval = INLINE_SYSCALL (mq_notify, 2, mqdes, &se);
272
273 /* If it failed, free the allocated memory. */
274 if (__glibc_unlikely (retval != 0))
275 free (data.attr);
276
277 return retval;
278}
279
280#else
281# include <rt/mq_notify.c>
282#endif
283