[PATCH v2 2/7] common: add scoped_mmap

[Markus Metzger <markus.t.metzger@intel.com>]

Add a simple helper to automatically unmap a memory mapping.

2018-01-26  Markus Metzger  <markus.t.metzger@intel.com>

gdb/
	* common/scoped_mmap.h: New.
	* unittests/scoped_mmap-selftest.c: New.
	* Makefile.in (SUBDIR_UNITTESTS_SRCS): Add
	unittests/scoped_mmap-selftest.c.

---
 gdb/Makefile.in                       |  1 +
 gdb/common/scoped_mmap.h              | 76 +++++++++++++++++++++++++++++
 gdb/unittests/scoped_mmap-selftests.c | 92 +++++++++++++++++++++++++++++++++++
 3 files changed, 169 insertions(+)
 create mode 100644 gdb/common/scoped_mmap.h
 create mode 100644 gdb/unittests/scoped_mmap-selftests.c

diff --git a/gdb/Makefile.in b/gdb/Makefile.in
index a982cdf5..957654c 100644
--- a/gdb/Makefile.in
+++ b/gdb/Makefile.in
@@ -425,6 +425,7 @@ SUBDIR_UNITTESTS_SRCS = \
 	unittests/ptid-selftests.c \
 	unittests/rsp-low-selftests.c \
 	unittests/scoped_fd-selftests.c \
+	unittests/scoped_mmap-selftests.c \
 	unittests/scoped_restore-selftests.c \
 	unittests/xml-utils-selftests.c
 
diff --git a/gdb/common/scoped_mmap.h b/gdb/common/scoped_mmap.h
new file mode 100644
index 0000000..739cc70
--- /dev/null
+++ b/gdb/common/scoped_mmap.h
@@ -0,0 +1,76 @@
+/* scoped_mmap, automatically unmap files
+
+   Copyright (C) 2018 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/>.  */
+
+#ifndef SCOPED_MMAP_H
+#define SCOPED_MMAP_H
+
+#include "config.h"
+
+#ifdef HAVE_SYS_MMAN_H
+
+#include <sys/mman.h>
+
+/* A smart-pointer-like class to mmap() and automatically munmap() a memory
+   mapping.  */
+
+class scoped_mmap
+{
+public:
+  scoped_mmap () noexcept : m_mem (MAP_FAILED), m_length (0) {}
+  scoped_mmap (void *addr, size_t length, int prot, int flags, int fd,
+	       off_t offset) noexcept : m_length (length)
+    {
+      m_mem = mmap (addr, m_length, prot, flags, fd, offset);
+    }
+  ~scoped_mmap ()
+    {
+      if (m_mem != MAP_FAILED)
+	munmap (m_mem, m_length);
+    }
+
+  DISABLE_COPY_AND_ASSIGN (scoped_mmap);
+
+  void *release () noexcept
+    {
+      void *mem = m_mem;
+      m_mem = MAP_FAILED;
+      m_length = 0;
+      return mem;
+    }
+
+  void reset (void *addr, size_t length, int prot, int flags, int fd,
+	      off_t offset) noexcept
+    {
+      if (m_mem != MAP_FAILED)
+	munmap (m_mem, m_length);
+
+      m_length = length;
+      m_mem = mmap (addr, m_length, prot, flags, fd, offset);
+    }
+
+  size_t size () const noexcept { return m_length; }
+  void *get () const noexcept { return m_mem; }
+
+private:
+  void *m_mem;
+  size_t m_length;
+};
+
+#endif /* HAVE_SYS_MMAN_H */
+#endif /* SCOPED_MMAP_H */
diff --git a/gdb/unittests/scoped_mmap-selftests.c b/gdb/unittests/scoped_mmap-selftests.c
new file mode 100644
index 0000000..ece3d7a
--- /dev/null
+++ b/gdb/unittests/scoped_mmap-selftests.c
@@ -0,0 +1,92 @@
+/* Self tests for scoped_mmap for GDB, the GNU debugger.
+
+   Copyright (C) 2018 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 "defs.h"
+
+#include "common/scoped_mmap.h"
+#include "config.h"
+
+#if defined(HAVE_SYS_MMAN_H) && defined(HAVE_UNISTD_H)
+
+#include "selftest.h"
+
+#include <unistd.h>
+
+namespace selftests {
+namespace scoped_mmap {
+
+/* Test that the file is unmapped.  */
+static void
+test_destroy ()
+{
+  void *mem;
+
+  errno = 0;
+  {
+    ::scoped_mmap smmap (nullptr, sysconf (_SC_PAGESIZE), PROT_WRITE,
+			 MAP_ANONYMOUS | MAP_PRIVATE, 0, 0);
+
+    mem = smmap.get ();
+    SELF_CHECK (mem != nullptr);
+  }
+
+  SELF_CHECK (msync (mem, sysconf (_SC_PAGESIZE), 0) == -1 && errno == ENOMEM);
+}
+
+/* Test that the memory can be released.  */
+static void
+test_release ()
+{
+  void *mem;
+
+  errno = 0;
+  {
+    ::scoped_mmap smmap (nullptr, sysconf (_SC_PAGESIZE), PROT_WRITE,
+			 MAP_ANONYMOUS | MAP_PRIVATE, 0, 0);
+
+    mem = smmap.release ();
+    SELF_CHECK (mem != nullptr);
+  }
+
+  SELF_CHECK (msync (mem, sysconf (_SC_PAGESIZE), 0) == 0 || errno != ENOMEM);
+
+  munmap (mem, sysconf (_SC_PAGESIZE));
+}
+
+/* Run selftests.  */
+static void
+run_tests ()
+{
+  test_destroy ();
+  test_release ();
+}
+
+} /* namespace scoped_mmap */
+} /* namespace selftests */
+
+#endif /* !defined(HAVE_SYS_MMAN_H) || !defined(HAVE_UNISTD_H) */
+
+void
+_initialize_scoped_mmap_selftests ()
+{
+#if defined(HAVE_SYS_MMAN_H) && defined(HAVE_UNISTD_H)
+  selftests::register_test ("scoped_mmap",
+			    selftests::scoped_mmap::run_tests);
+#endif
+}
-- 
1.8.3.1