sysdeps/unix/sysv/linux/mq_notify.c

   1 /* Copyright (C) 2004-2017 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.  */
  44 union 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.  */
  59 static pthread_once_t once = PTHREAD_ONCE_INIT;
  60
  61
  62 /* The netlink socket.  */
  63 static 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.  */
  68 static 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.  */
  74 static int
  75 __attribute__ ((noinline))
  76 change_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.  */
  85 static void *
  86 notification_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.  */
 113 static void *
 114 helper_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
 145 static void
 146 reset_once (void)
 147 {
 148   once = PTHREAD_ONCE_INIT;
 149 }
 150
 151
 152 static void
 153 init_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.  */
 220 int
 221 mq_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