gdbsupport: Add an event-pipe class.

This pulls out the implementation of an event pipe used to implement
target async support in both linux-low.cc (gdbserver) and linux-nat.c
(gdb).

This will be used to replace the existing event pipe in linux-low.cc
and linux-nat.c in future commits.

Co-Authored-By: Lancelot SIX <lsix@lancelotsix.com>

1 files changed, 101 insertions, 0 deletions

diff --git a/gdbsupport/event-pipe.cc b/gdbsupport/event-pipe.cc
new file mode 100644
index 0000000..2b56b2f
--- /dev/null
+++ b/gdbsupport/event-pipe.cc
@@ -0,0 +1,101 @@
+/* Event pipe for GDB, the GNU debugger.
+
+   Copyright (C) 2021 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   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 3 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, see <http://www.gnu.org/licenses/>.  */
+
+#include "gdbsupport/common-defs.h"
+#include "gdbsupport/event-pipe.h"
+#include "gdbsupport/filestuff.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+event_pipe::~event_pipe ()
+{
+  if (is_open ())
+    close ();
+}
+
+/* See event-pipe.h.  */
+
+bool
+event_pipe::open ()
+{
+  if (is_open ())
+    return false;
+
+  if (gdb_pipe_cloexec (m_fds) == -1)
+    return false;
+
+  if (fcntl (m_fds[0], F_SETFL, O_NONBLOCK) == -1
+      || fcntl (m_fds[1], F_SETFL, O_NONBLOCK) == -1)
+    {
+      close ();
+      return false;
+    }
+
+  return true;
+}
+
+/* See event-pipe.h.  */
+
+void
+event_pipe::close ()
+{
+  ::close (m_fds[0]);
+  ::close (m_fds[1]);
+  m_fds[0] = -1;
+  m_fds[1] = -1;
+}
+
+/* See event-pipe.h.  */
+
+void
+event_pipe::flush ()
+{
+  int ret;
+  char buf;
+
+  do
+    {
+      ret = read (m_fds[0], &buf, 1);
+    }
+  while (ret >= 0 || (ret == -1 && errno == EINTR));
+}
+
+/* See event-pipe.h.  */
+
+void
+event_pipe::mark ()
+{
+  int ret;
+
+  /* It doesn't really matter what the pipe contains, as long we end
+     up with something in it.  Might as well flush the previous
+     left-overs.  */
+  flush ();
+
+  do
+    {
+      ret = write (m_fds[1], "+", 1);
+    }
+  while (ret == -1 && errno == EINTR);
+
+  /* Ignore EAGAIN.  If the pipe is full, the event loop will already
+     be awakened anyway.  */
+}