raw-posix: add discard support

Add support to discard blocks in a raw image residing on an XFS filesystem
by calling the XFS_IOC_UNRESVSP64 ioctl to punch holes.  Support for other
hole punching mechanisms can be added when they become available.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/configure b/configure
index 62defc4..47e4cf0 100755
--- a/configure
+++ b/configure
@@ -288,6 +288,7 @@
 linux_aio=""
 attr=""
 vhost_net=""
+xfs=""
 
 gprof="no"
 debug_tcg="no"
@@ -1399,6 +1400,27 @@
 fi
 
 ##########################################
+# xfsctl() probe, used for raw-posix
+if test "$xfs" != "no" ; then
+  cat > $TMPC << EOF
+#include <xfs/xfs.h>
+int main(void)
+{
+    xfsctl(NULL, 0, 0, NULL);
+    return 0;
+}
+EOF
+  if compile_prog "" "" ; then
+    xfs="yes"
+  else
+    if test "$xfs" = "yes" ; then
+      feature_not_found "xfs"
+    fi
+    xfs=no
+  fi
+fi
+
+##########################################
 # vde libraries probe
 if test "$vde" != "no" ; then
   vde_libs="-lvdeplug"
@@ -2403,6 +2425,7 @@
 echo "Trace output file $trace_file-<pid>"
 echo "spice support     $spice"
 echo "rbd support       $rbd"
+echo "xfsctl support    $xfs"
 
 if test $sdl_too_old = "yes"; then
 echo "-> Your SDL version is too old - please upgrade to have SDL support"
@@ -2548,6 +2571,9 @@
 if test "$uuid" = "yes" ; then
   echo "CONFIG_UUID=y" >> $config_host_mak
 fi
+if test "$xfs" = "yes" ; then
+  echo "CONFIG_XFS=y" >> $config_host_mak
+fi
 qemu_version=`head $source_path/VERSION`
 echo "VERSION=$qemu_version" >>$config_host_mak
 echo "PKGVERSION=$pkgversion" >>$config_host_mak