diff options
Diffstat (limited to 'sysdeps/unix/sysv/linux/mq_notify.c')
| -rw-r--r-- | sysdeps/unix/sysv/linux/mq_notify.c | 251 |
1 files changed, 245 insertions, 6 deletions
diff --git a/sysdeps/unix/sysv/linux/mq_notify.c b/sysdeps/unix/sysv/linux/mq_notify.c index a61839f507..d50a9f2d57 100644 --- a/sysdeps/unix/sysv/linux/mq_notify.c +++ b/sysdeps/unix/sysv/linux/mq_notify.c @@ -1,5 +1,6 @@ /* Copyright (C) 2004-2014 Free Software Foundation, Inc. This file is part of the GNU C Library. + Contribute by Ulrich Drepper <drepper@redhat.com>, 2004. The GNU C Library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public @@ -15,27 +16,265 @@ License along with the GNU C Library; if not, see <http://www.gnu.org/licenses/>. */ +#include <assert.h> #include <errno.h> +#include <fcntl.h> #include <mqueue.h> -#include <stddef.h> +#include <pthread.h> +#include <signal.h> +#include <stdlib.h> +#include <string.h> #include <sysdep.h> +#include <unistd.h> +#include <sys/socket.h> +#include <not-cancel.h> +#include <nptl/pthreadP.h> + #ifdef __NR_mq_notify +/* Defined in the kernel headers: */ +#define NOTIFY_COOKIE_LEN 32 /* Length of the cookie used. */ +#define NOTIFY_WOKENUP 1 /* Code for notifcation. */ +#define NOTIFY_REMOVED 2 /* Code for closed message queue + of de-notifcation. */ + + +/* Data structure for the queued notification requests. */ +union notify_data +{ + struct + { + void (*fct) (union sigval); /* The function to run. */ + union sigval param; /* The parameter to pass. */ + pthread_attr_t *attr; /* Attributes to create the thread with. */ + /* NB: on 64-bit machines the struct as a size of 24 bytes. Which means + byte 31 can still be used for returning the status. */ + }; + char raw[NOTIFY_COOKIE_LEN]; +}; + + +/* Keep track of the initialization. */ +static pthread_once_t once = PTHREAD_ONCE_INIT; + + +/* The netlink socket. */ +static int netlink_socket = -1; + + +/* Barrier used to make sure data passed to the new thread is not + resused by the parent. */ +static pthread_barrier_t notify_barrier; + + +/* Modify the signal mask. We move this into a separate function so + that the stack space needed for sigset_t is not deducted from what + the thread can use. */ +static int +__attribute__ ((noinline)) +change_sigmask (int how, sigset_t *oss) +{ + sigset_t ss; + sigfillset (&ss); + return pthread_sigmask (how, &ss, oss); +} + + +/* The function used for the notification. */ +static void * +notification_function (void *arg) +{ + /* Copy the function and parameter so that the parent thread can go + on with its life. */ + volatile union notify_data *data = (volatile union notify_data *) arg; + void (*fct) (union sigval) = data->fct; + union sigval param = data->param; + + /* Let the parent go. */ + (void) pthread_barrier_wait (¬ify_barrier); + + /* Make the thread detached. */ + (void) pthread_detach (pthread_self ()); + + /* The parent thread has all signals blocked. This is probably a + bit surprising for this thread. So we unblock all of them. */ + (void) change_sigmask (SIG_UNBLOCK, NULL); + + /* Now run the user code. */ + fct (param); + + /* And we are done. */ + return NULL; +} + + +/* Helper thread. */ +static void * +helper_thread (void *arg) +{ + while (1) + { + union notify_data data; + + ssize_t n = recv (netlink_socket, &data, sizeof (data), + MSG_NOSIGNAL | MSG_WAITALL); + if (n < NOTIFY_COOKIE_LEN) + continue; + + if (data.raw[NOTIFY_COOKIE_LEN - 1] == NOTIFY_WOKENUP) + { + /* Just create the thread as instructed. There is no way to + report a problem with creating a thread. */ + pthread_t th; + if (__builtin_expect (pthread_create (&th, data.attr, + notification_function, &data) + == 0, 0)) + /* Since we passed a pointer to DATA to the new thread we have + to wait until it is done with it. */ + (void) pthread_barrier_wait (¬ify_barrier); + } + else if (data.raw[NOTIFY_COOKIE_LEN - 1] == NOTIFY_REMOVED) + /* The only state we keep is the copy of the thread attributes. */ + free (data.attr); + } + return NULL; +} + + +static void +reset_once (void) +{ + once = PTHREAD_ONCE_INIT; +} + + +static void +init_mq_netlink (void) +{ + /* This code might be called a second time after fork(). The file + descriptor is inherited from the parent. */ + if (netlink_socket == -1) + { + /* Just a normal netlink socket, not bound. */ + netlink_socket = socket (AF_NETLINK, SOCK_RAW | SOCK_CLOEXEC, 0); + /* No need to do more if we have no socket. */ + if (netlink_socket == -1) + return; + } + + int err = 1; + + /* Initialize the barrier. */ + if (__builtin_expect (pthread_barrier_init (¬ify_barrier, NULL, 2) == 0, + 0)) + { + /* Create the helper thread. */ + pthread_attr_t attr; + (void) pthread_attr_init (&attr); + (void) pthread_attr_setdetachstate (&attr, PTHREAD_CREATE_DETACHED); + /* We do not need much stack space, the bare minimum will be enough. */ + (void) pthread_attr_setstacksize (&attr, __pthread_get_minstack (&attr)); + + /* Temporarily block all signals so that the newly created + thread inherits the mask. */ + sigset_t oss; + int have_no_oss = change_sigmask (SIG_BLOCK, &oss); + + pthread_t th; + err = pthread_create (&th, &attr, helper_thread, NULL); + + /* Reset the signal mask. */ + if (!have_no_oss) + pthread_sigmask (SIG_SETMASK, &oss, NULL); + + (void) pthread_attr_destroy (&attr); + + if (err == 0) + { + static int added_atfork; + + if (added_atfork == 0 + && pthread_atfork (NULL, NULL, reset_once) != 0) + { + /* The child thread will call recv() which is a + cancellation point. */ + (void) pthread_cancel (th); + err = 1; + } + else + added_atfork = 1; + } + } + + if (err != 0) + { + close_not_cancel_no_status (netlink_socket); + netlink_socket = -1; + } +} + + /* Register notification upon message arrival to an empty message queue MQDES. */ int mq_notify (mqd_t mqdes, const struct sigevent *notification) { - /* mq_notify which handles SIGEV_THREAD is included in the thread - add-on. */ - if (notification != NULL - && notification->sigev_notify == SIGEV_THREAD) + /* Make sure the type is correctly defined. */ + assert (sizeof (union notify_data) == NOTIFY_COOKIE_LEN); + + /* Special treatment needed for SIGEV_THREAD. */ + if (notification == NULL || notification->sigev_notify != SIGEV_THREAD) + return INLINE_SYSCALL (mq_notify, 2, mqdes, notification); + + /* The kernel cannot directly start threads. This will have to be + done at userlevel. Since we cannot start threads from signal + handlers we have to create a dedicated thread which waits for + notifications for arriving messages and creates threads in + response. */ + + /* Initialize only once. */ + pthread_once (&once, init_mq_netlink); + + /* If we cannot create the netlink socket we cannot provide + SIGEV_THREAD support. */ + if (__glibc_unlikely (netlink_socket == -1)) { __set_errno (ENOSYS); return -1; } - return INLINE_SYSCALL (mq_notify, 2, mqdes, notification); + + /* Create the cookie. It will hold almost all the state. */ + union notify_data data; + memset (&data, '\0', sizeof (data)); + data.fct = notification->sigev_notify_function; + data.param = notification->sigev_value; + + if (notification->sigev_notify_attributes != NULL) + { + /* The thread attribute has to be allocated separately. */ + data.attr = (pthread_attr_t *) malloc (sizeof (pthread_attr_t)); + if (data.attr == NULL) + return -1; + + memcpy (data.attr, notification->sigev_notify_attributes, + sizeof (pthread_attr_t)); + } + + /* Construct the new request. */ + struct sigevent se; + se.sigev_notify = SIGEV_THREAD; + se.sigev_signo = netlink_socket; + se.sigev_value.sival_ptr = &data; + + /* Tell the kernel. */ + int retval = INLINE_SYSCALL (mq_notify, 2, mqdes, &se); + + /* If it failed, free the allocated memory. */ + if (__glibc_unlikely (retval != 0)) + free (data.attr); + + return retval; } #else |