memfd: add workaround for systems without memfd

Just a quick workaround to use a tmpfile if memfd is not available. We
should try to ensure that we get something on tmpfs, but this is probably
good enough for a fallback.

lib/Makefile.am

@@ -87,6 +87,8 @@ libsysprof_@API_VERSION@_la_SOURCES = \
 	sp-perf-counter.c \
 	sp-perf-counter.h \
 	sp-perf-source.c \
+	sp-platform.c \
+	sp-platform.h \
 	sp-proc-source.c \
 	sp-profile.c \
 	sp-profiler.c \

lib/sp-local-profiler.c

@@ -19,10 +19,10 @@
 #include <glib.h>
 #include <glib/gstdio.h>
 #include <errno.h>
-#include <sys/syscall.h>
 #include <unistd.h>
 
 #include "sp-local-profiler.h"
+#include "sp-platform.h"
 
 typedef struct
 {
@@ -467,7 +467,7 @@ sp_local_profiler_start (SpProfiler *profiler)
       SpCaptureWriter *writer;
       int fd;
 
-      if ((-1 == (fd = syscall (__NR_memfd_create, "[sysprof]", 0))) ||
+      if ((-1 == (fd = sp_memfd_create ("[sysprof]"))) ||
           (NULL == (writer = sp_capture_writer_new_from_fd (fd, 0))))
         {
           const GError error = {

lib/sp-platform.c

@@ -0,0 +1,63 @@
+/* sp-platform.c
+ *
+ * Copyright (C) 2016 Christian Hergert <christian@hergert.me>
+ *
+ * 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 <sys/syscall.h>
+#include <unistd.h>
+
+#include "sp-platform.h"
+
+/**
+ * sp_memfd_create:
+ * @name: (nullable): A descriptive name for the memfd or %NULL
+ *
+ * Creates a new memfd using the memfd_create syscall if available.
+ * Otherwise, a tmpfile is used. Currently, no attempt is made to
+ * ensure the tmpfile is on a tmpfs backed mount.
+ *
+ * Returns: An fd if successful; otherwise -1 and errno is set.
+ */
+int
+sp_memfd_create (const gchar *name)
+{
+#ifdef __NR_memfd_create
+  if (name == NULL)
+    name = "[sysprof]";
+  return syscall (__NR_memfd_create, name, 0);
+#else
+  gchar *name_used = NULL;
+  int fd;
+
+  /*
+   * TODO: It would be nice to ensure tmpfs
+   *
+   * It is not strictly required that the preferred temporary directory
+   * will be mounted as tmpfs. We should look through the mounts and ensure
+   * that the tmpfile we open is on tmpfs so that we get anonymous backed
+   * pages after unlinking.
+   */
+  fd = g_file_open_tmp (NULL, &name_used, NULL);
+
+  if (name_used != NULL)
+    {
+      g_unlink (name_used);
+      g_free (name_used)
+    }
+
+  return fd;
+#endif
+}

lib/sp-platform.h

@@ -0,0 +1,30 @@
+/* sp-platform.h
+ *
+ * Copyright (C) 2016 Christian Hergert <christian@hergert.me>
+ *
+ * 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 SP_PLATFORM_H
+#define SP_PLATFORM_H
+
+#include <glib.h>
+
+G_BEGIN_DECLS
+
+int sp_memfd_create (const gchar *desc);
+
+G_END_DECLS
+
+#endif /* SP_PLATFORM_H */