--- /dev/null
+/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */
+/* dbus-socket-set-epoll.c - a socket set implemented via Linux epoll(4)
+ *
+ * Copyright © 2011 Nokia Corporation
+ *
+ * Licensed under the Academic Free License version 2.1
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
+ * MA 02110-1301 USA
+ *
+ */
+
+#include <config.h>
+#include "dbus-socket-set.h"
+
+#include <dbus/dbus-internals.h>
+#include <dbus/dbus-sysdeps.h>
+
+#ifndef __linux__
+# error This file is for Linux epoll(4)
+#endif
+
+#include <errno.h>
+#include <sys/epoll.h>
+#include <unistd.h>
+
+#ifndef DOXYGEN_SHOULD_SKIP_THIS
+
+typedef struct {
+ DBusSocketSet parent;
+ int epfd;
+} DBusSocketSetEpoll;
+
+static inline DBusSocketSetEpoll *
+socket_set_epoll_cast (DBusSocketSet *set)
+{
+ _dbus_assert (set->cls == &_dbus_socket_set_epoll_class);
+ return (DBusSocketSetEpoll *) set;
+}
+
+/* this is safe to call on a partially-allocated socket set */
+static void
+socket_set_epoll_free (DBusSocketSet *set)
+{
+ DBusSocketSetEpoll *self = socket_set_epoll_cast (set);
+
+ if (self == NULL)
+ return;
+
+ if (self->epfd != -1)
+ close (self->epfd);
+
+ dbus_free (self);
+}
+
+DBusSocketSet *
+_dbus_socket_set_epoll_new (void)
+{
+ DBusSocketSetEpoll *self;
+
+ self = dbus_new0 (DBusSocketSetEpoll, 1);
+
+ if (self == NULL)
+ return NULL;
+
+ self->parent.cls = &_dbus_socket_set_epoll_class;
+
+ self->epfd = epoll_create1 (EPOLL_CLOEXEC);
+
+ if (self->epfd == -1)
+ {
+ socket_set_epoll_free ((DBusSocketSet *) self);
+ return NULL;
+ }
+
+ return (DBusSocketSet *) self;
+}
+
+static uint32_t
+watch_flags_to_epoll_events (unsigned int flags)
+{
+ uint32_t events = 0;
+
+ if (flags & DBUS_WATCH_READABLE)
+ events |= EPOLLIN;
+ if (flags & DBUS_WATCH_WRITABLE)
+ events |= EPOLLOUT;
+
+ return events;
+}
+
+static unsigned int
+epoll_events_to_watch_flags (uint32_t events)
+{
+ short flags = 0;
+
+ if (events & EPOLLIN)
+ flags |= DBUS_WATCH_READABLE;
+ if (events & EPOLLOUT)
+ flags |= DBUS_WATCH_WRITABLE;
+ if (events & EPOLLHUP)
+ flags |= DBUS_WATCH_HANGUP;
+ if (events & EPOLLERR)
+ flags |= DBUS_WATCH_ERROR;
+
+ return flags;
+}
+
+static dbus_bool_t
+socket_set_epoll_add (DBusSocketSet *set,
+ int fd,
+ unsigned int flags,
+ dbus_bool_t enabled)
+{
+ DBusSocketSetEpoll *self = socket_set_epoll_cast (set);
+ struct epoll_event event;
+ int err;
+
+ event.data.fd = fd;
+
+ if (enabled)
+ {
+ event.events = watch_flags_to_epoll_events (flags);
+ }
+ else
+ {
+ /* We need to add *something* to reserve space in the kernel's data
+ * structures: see socket_set_epoll_disable for more details */
+ event.events = EPOLLET;
+ }
+
+ if (epoll_ctl (self->epfd, EPOLL_CTL_ADD, fd, &event) == 0)
+ return TRUE;
+
+ /* Anything except ENOMEM, ENOSPC means we have an internal error. */
+ err = errno;
+ switch (err)
+ {
+ case ENOMEM:
+ case ENOSPC:
+ /* be silent: this is basically OOM, which our callers are expected
+ * to cope with */
+ break;
+
+ case EBADF:
+ _dbus_warn ("Bad fd %d\n", fd);
+ break;
+
+ case EEXIST:
+ _dbus_warn ("fd %d added and then added again\n", fd);
+ break;
+
+ default:
+ _dbus_warn ("Misc error when trying to watch fd %d: %s\n", fd,
+ strerror (err));
+ break;
+ }
+
+ return FALSE;
+}
+
+static void
+socket_set_epoll_enable (DBusSocketSet *set,
+ int fd,
+ unsigned int flags)
+{
+ DBusSocketSetEpoll *self = socket_set_epoll_cast (set);
+ struct epoll_event event;
+ int err;
+
+ event.data.fd = fd;
+ event.events = watch_flags_to_epoll_events (flags);
+
+ if (epoll_ctl (self->epfd, EPOLL_CTL_MOD, fd, &event) == 0)
+ return;
+
+ err = errno;
+
+ /* Enabling a file descriptor isn't allowed to fail, even for OOM, so we
+ * do our best to avoid all of these. */
+ switch (err)
+ {
+ case EBADF:
+ _dbus_warn ("Bad fd %d\n", fd);
+ break;
+
+ case ENOENT:
+ _dbus_warn ("fd %d enabled before it was added\n", fd);
+ break;
+
+ case ENOMEM:
+ _dbus_warn ("Insufficient memory to change watch for fd %d\n", fd);
+ break;
+
+ default:
+ _dbus_warn ("Misc error when trying to watch fd %d: %s\n", fd,
+ strerror (err));
+ break;
+ }
+}
+
+static void
+socket_set_epoll_disable (DBusSocketSet *set,
+ int fd)
+{
+ DBusSocketSetEpoll *self = socket_set_epoll_cast (set);
+ struct epoll_event event;
+ int err;
+
+ /* The naive thing to do would be EPOLL_CTL_DEL, but that'll probably
+ * free resources in the kernel. When we come to do socket_set_epoll_enable,
+ * there might not be enough resources to bring it back!
+ *
+ * The next idea you might have is to set the flags to 0. However, events
+ * always trigger on EPOLLERR and EPOLLHUP, even if libdbus isn't actually
+ * delivering them to a DBusWatch. Because epoll is level-triggered by
+ * default, we'll busy-loop on an unhandled error or hangup; not good.
+ *
+ * So, let's set it to be edge-triggered: then the worst case is that
+ * we return from poll immediately on one iteration, ignore it because no
+ * watch is enabled, then go back to normal. When we re-enable a watch
+ * we'll switch back to level-triggered and be notified again (verified to
+ * work on 2.6.32). Compile this file with -DTEST_BEHAVIOUR_OF_EPOLLET for
+ * test code.
+ */
+ event.data.fd = fd;
+ event.events = EPOLLET;
+
+ if (epoll_ctl (self->epfd, EPOLL_CTL_MOD, fd, &event) == 0)
+ return;
+
+ err = errno;
+ _dbus_warn ("Error when trying to watch fd %d: %s\n", fd,
+ strerror (err));
+}
+
+static void
+socket_set_epoll_remove (DBusSocketSet *set,
+ int fd)
+{
+ DBusSocketSetEpoll *self = socket_set_epoll_cast (set);
+ int err;
+
+ if (epoll_ctl (self->epfd, EPOLL_CTL_DEL, fd, NULL) == 0)
+ return;
+
+ err = errno;
+ _dbus_warn ("Error when trying to remove fd %d: %s\n", fd, strerror (err));
+}
+
+/* Optimally, this should be the same as in DBusLoop: we use it to translate
+ * between struct epoll_event and DBusSocketEvent without allocating heap
+ * memory. */
+#define N_STACK_DESCRIPTORS 64
+
+static int
+socket_set_epoll_poll (DBusSocketSet *set,
+ DBusSocketEvent *revents,
+ int max_events,
+ int timeout_ms)
+{
+ DBusSocketSetEpoll *self = socket_set_epoll_cast (set);
+ struct epoll_event events[N_STACK_DESCRIPTORS];
+ int n_ready;
+ int i;
+
+ _dbus_assert (max_events > 0);
+
+ n_ready = epoll_wait (self->epfd, events,
+ MIN (_DBUS_N_ELEMENTS (events), max_events),
+ timeout_ms);
+
+ if (n_ready <= 0)
+ return n_ready;
+
+ for (i = 0; i < n_ready; i++)
+ {
+ revents[i].fd = events[i].data.fd;
+ revents[i].flags = epoll_events_to_watch_flags (events[i].events);
+ }
+
+ return n_ready;
+}
+
+DBusSocketSetClass _dbus_socket_set_epoll_class = {
+ socket_set_epoll_free,
+ socket_set_epoll_add,
+ socket_set_epoll_remove,
+ socket_set_epoll_enable,
+ socket_set_epoll_disable,
+ socket_set_epoll_poll
+};
+
+#ifdef TEST_BEHAVIOUR_OF_EPOLLET
+/* usage: cat /dev/null | ./epoll
+ *
+ * desired output:
+ * ctl ADD: 0
+ * wait for HUP, edge-triggered: 1
+ * wait for HUP again: 0
+ * ctl MOD: 0
+ * wait for HUP: 1
+ */
+
+#include <sys/epoll.h>
+
+#include <stdio.h>
+
+int
+main (void)
+{
+ struct epoll_event input;
+ struct epoll_event output;
+ int epfd = epoll_create1 (EPOLL_CLOEXEC);
+ int fd = 0; /* stdin */
+ int ret;
+
+ input.events = EPOLLHUP | EPOLLET;
+ ret = epoll_ctl (epfd, EPOLL_CTL_ADD, fd, &input);
+ printf ("ctl ADD: %d\n", ret);
+
+ ret = epoll_wait (epfd, &output, 1, -1);
+ printf ("wait for HUP, edge-triggered: %d\n", ret);
+
+ ret = epoll_wait (epfd, &output, 1, 1);
+ printf ("wait for HUP again: %d\n", ret);
+
+ input.events = EPOLLHUP;
+ ret = epoll_ctl (epfd, EPOLL_CTL_MOD, fd, &input);
+ printf ("ctl MOD: %d\n", ret);
+
+ ret = epoll_wait (epfd, &output, 1, -1);
+ printf ("wait for HUP: %d\n", ret);
+
+ return 0;
+}
+
+#endif /* TEST_BEHAVIOUR_OF_EPOLLET */
+
+#endif /* !DOXYGEN_SHOULD_SKIP_THIS */
projects / platform / upstream / dbus.git / commitdiff