Attachment 42533 Details for Bug 33337 – [3/5] Add an implementation of DBusSocketSet using epoll

[patch] [3/5] Add an implementation of DBusSocketSet using epoll

0003-Add-an-implementation-of-DBusSocketSet-using-epoll.patch (text/plain), 9.42 KB, created by Simon McVittie on 2011-01-26 09:12:45 UTC

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Creator: Simon McVittie

Created: 2011-01-26 09:12:45 UTC

Size: 9.42 KB

patch

obsolete

>From 3fc85e265f67448a28429d75de500c468dc4c56a Mon Sep 17 00:00:00 2001
>From: Simon McVittie <simon.mcvittie@collabora.co.uk>
>Date: Wed, 26 Jan 2011 16:29:04 +0000
>Subject: [PATCH 3/5] Add an implementation of DBusSocketSet using epoll
>
>---
> dbus/Makefile.am             |    7 +-
> dbus/dbus-socket-set-epoll.c |  314 ++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 320 insertions(+), 1 deletions(-)
> create mode 100644 dbus/dbus-socket-set-epoll.c
>
>diff --git a/dbus/Makefile.am b/dbus/Makefile.am
>index 7693c8a..7ef2b8e 100644
>--- a/dbus/Makefile.am
>+++ b/dbus/Makefile.am
>@@ -106,6 +106,12 @@ DBUS_UTIL_arch_sources = 			\
> 	dbus-spawn.c
> endif
> 
>+if HAVE_LINUX_EPOLL
>+DBUS_UTIL_arch_sources += dbus-socket-set-epoll.c
>+else
>+DBUS_UTIL_arch_sources += dbus-socket-set-poll.c
>+endif
>+
> dbusinclude_HEADERS=				\
> 	dbus.h					\
> 	dbus-address.h				\
>@@ -238,7 +244,6 @@ DBUS_UTIL_SOURCES=				\
> 	dbus-shell.h				\
> 	$(DBUS_UTIL_arch_sources)		\
> 	dbus-socket-set.h			\
>-	dbus-socket-set-poll.c			\
> 	dbus-spawn.h				\
> 	dbus-string-util.c			\
> 	dbus-sysdeps-util.c			\
>diff --git a/dbus/dbus-socket-set-epoll.c b/dbus/dbus-socket-set-epoll.c
>new file mode 100644
>index 0000000..0c6745f
>--- /dev/null
>+++ b/dbus/dbus-socket-set-epoll.c
>@@ -0,0 +1,314 @@
>+/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */
>+/* dbus-socket-set-epoll.c - a socket set implemented via Linux epoll(4)
>+ *
>+ * Copyright Â© 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
>+
>+DBusSocketSet *
>+_dbus_socket_set_new (int size_hint)
>+{
>+  int epfd = epoll_create1 (EPOLL_CLOEXEC);
>+
>+  if (epfd == -1)
>+    return NULL;
>+
>+  return _DBUS_INT_TO_POINTER (epfd);
>+}
>+
>+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;
>+}
>+
>+dbus_bool_t
>+_dbus_socket_set_add (DBusSocketSet  *self,
>+                      int             fd,
>+                      unsigned int    flags,
>+                      dbus_bool_t     enabled)
>+{
>+  int epfd = _DBUS_POINTER_TO_INT (self);
>+  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 _dbus_socket_set_disable for more details */
>+      event.events = EPOLLET;
>+    }
>+
>+  if (epoll_ctl (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;
>+}
>+
>+void
>+_dbus_socket_set_enable (DBusSocketSet  *self,
>+                         int             fd,
>+                         unsigned int    flags)
>+{
>+  int epfd = _DBUS_POINTER_TO_INT (self);
>+  struct epoll_event event;
>+  int err;
>+
>+  event.data.fd = fd;
>+  event.events = watch_flags_to_epoll_events (flags);
>+
>+  if (epoll_ctl (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 modified 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;
>+    }
>+}
>+
>+void
>+_dbus_socket_set_disable (DBusSocketSet  *self,
>+                          int             fd)
>+{
>+  int epfd = _DBUS_POINTER_TO_INT (self);
>+  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 _dbus_socket_set_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 (epfd, EPOLL_CTL_MOD, fd, &event) == 0)
>+    return;
>+
>+  err = errno;
>+  _dbus_warn ("Error when trying to watch fd %d: %s\n", fd,
>+              strerror (err));
>+}
>+
>+void
>+_dbus_socket_set_remove (DBusSocketSet  *self,
>+                         int             fd)
>+{
>+  int epfd = _DBUS_POINTER_TO_INT (self);
>+  int err;
>+
>+  if (epoll_ctl (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. This is a bit stupid,
>+ * but it makes things simpler... */
>+#define N_STACK_DESCRIPTORS 64
>+
>+/** This is basically Linux's epoll_wait(2) implemented in terms of poll(2);
>+ * it returns results into a caller-supplied buffer so we can be reentrant. */
>+int
>+_dbus_socket_set_poll (DBusSocketSet   *self,
>+                       DBusSocketEvent *revents,
>+                       int              max_events,
>+                       int              timeout_ms)
>+{
>+  int epfd = _DBUS_POINTER_TO_INT (self);
>+  struct epoll_event events[N_STACK_DESCRIPTORS];
>+  int n_ready;
>+  int i;
>+
>+  _dbus_assert (max_events > 0);
>+
>+  n_ready = epoll_wait (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;
>+}
>+
>+/* this is safe to call on a partially-allocated socket set */
>+void
>+_dbus_socket_set_free (DBusSocketSet *self)
>+{
>+  int epfd = _DBUS_POINTER_TO_INT (self);
>+
>+  close (epfd);
>+}
>+
>+#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 */
>-- 
>1.7.2.3
>

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Attachments on bug 33337: 42531 | 42532 | 42533 | 42534 | 42535 | 42905 | 42906 | 45390 | 47907 | 47908 | 47909 | 47910 | 47911 | 47912 | 53061

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