[PATCH 2 of 3] blktap3/libxl: Check whether blktap3 is available

[Thanos Makatos <thanos.makatos@citrix.com>]

This patch implements function libxl__blktap3_enabled, the equivalent of the
existing libxl__blktap_enabled for blktap2. The checks performed are rather
simple and should be extended.

diff -r dd920505264c -r dd63f2992e71 tools/libxl/Makefile
--- a/tools/libxl/Makefile	Fri Feb 08 17:23:23 2013 +0000
+++ b/tools/libxl/Makefile	Fri Feb 08 17:23:25 2013 +0000
@@ -37,8 +37,10 @@ LIBXLU_LIBS =
 LIBXL_OBJS-y = osdeps.o libxl_paths.o libxl_bootloader.o flexarray.o
 ifeq ($(LIBXL_BLKTAP),y)
 LIBXL_OBJS-y += libxl_blktap2.o
+LIBXL_OBJS-y += libxl_blktap3.o
 else
 LIBXL_OBJS-y += libxl_noblktap2.o
+LIBXL_OBJS-y += libxl_noblktap3.o
 endif
 LIBXL_OBJS-$(CONFIG_X86) += libxl_cpuid.o libxl_x86.o
 LIBXL_OBJS-$(CONFIG_IA64) += libxl_nocpuid.o libxl_noarch.o
diff -r dd920505264c -r dd63f2992e71 tools/libxl/libxl_blktap3.c
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tools/libxl/libxl_blktap3.c	Fri Feb 08 17:23:25 2013 +0000
@@ -0,0 +1,60 @@
+/*
+ * Copyright (C) 2012      Citrix Ltd.
+ *
+ * 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 "libxl_osdeps.h" /* must come before any other headers */
+#include "libxl_internal.h"
+
+/* FIXME get the tapback name from blktap3 instead of hard-coding */
+#define TAPBACK_NAME "tapback"
+#define CMD "pidof " TAPBACK_NAME
+
+/*
+ * Simple sanity checks. Most of these checks are not race-free (e.g. checking
+ * wether the tapdisk binary exists), but at least we get some protection
+ * against spectacularly silly mistakes.
+ *
+ * We don't check whether the tapdisk binary exists as this is done by the
+ * tapback daemon.
+ */
+int libxl__blktap3_enabled(libxl__gc *gc)
+{
+    libxl_ctx *ctx = libxl__gc_owner(gc);
+    int err;
+
+    /*
+     * Check whether the tapback daemon is running.
+     */
+    err = system(CMD);
+    if (err == -1) {
+        LIBXL__LOG_ERRNO(ctx, LIBXL__LOG_ERROR,
+                "failed to check whether the tapback daemon is running\n");
+        return 0;
+    }
+    err = WEXITSTATUS(err);
+    if (err != 0) {
+        LIBXL__LOG(ctx, LIBXL__LOG_ERROR, "tapback daemon not running\n");
+        return 0;
+    }
+
+    /*
+     * TODO Check for evtchn, gntdev. How do we do that!?
+     */
+
+    return 1;
+}
diff -r dd920505264c -r dd63f2992e71 tools/libxl/libxl_internal.h
--- a/tools/libxl/libxl_internal.h	Fri Feb 08 17:23:23 2013 +0000
+++ b/tools/libxl/libxl_internal.h	Fri Feb 08 17:23:25 2013 +0000
@@ -1337,6 +1337,14 @@ struct libxl__cpuid_policy {
 };
 
 /*
+ * blktap3 support
+ */
+/* libxl__blktap_enabled:
+ *    return true if blktap3 support is available.
+ */
+_hidden int libxl__blktap3_enabled(libxl__gc *gc);
+
+/*
  * blktap2 support
  */
 
diff -r dd920505264c -r dd63f2992e71 tools/libxl/libxl_noblktap3.c
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tools/libxl/libxl_noblktap3.c	Fri Feb 08 17:23:25 2013 +0000
@@ -0,0 +1,26 @@
+/*
+ * Copyright (C) 2012      Citrix Ltd.
+ *
+ * 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 "libxl_osdeps.h" /* must come before any other headers */
+#include "libxl_internal.h"
+
+int libxl__blktap3_enabled(libxl__gc *gc)
+{
+    return 0;
+}