gluster: add support for PREALLOC_MODE_FALLOC

Add missing support for "preallocation=falloc" to the Gluster block
driver. This change bases its logic on that of block/file-posix.c and
removed the gluster_supports_zerofill() and qemu_gluster_zerofill()
functions in favour of #ifdef checks in an easy to read
switch-statement.

Both glfs_zerofill() and glfs_fallocate() have been introduced with
GlusterFS 3.5.0 (pkg-config glusterfs-api = 6). A #define for the
availability of glfs_fallocate() has been added to ./configure.

Reported-by: Satheesaran Sundaramoorthi <sasundar@redhat.com>
Signed-off-by: Niels de Vos <ndevos@redhat.com>
Message-id: 20170528063114.28691-1-ndevos@redhat.com
URL: https://bugzilla.redhat.com/1450759
Signed-off-by: Niels de Vos <ndevos@redhat.com>
Signed-off-by: Jeff Cody <jcody@redhat.com>
diff --git a/configure b/configure
index 0586ec9..21944ea 100755
--- a/configure
+++ b/configure
@@ -300,6 +300,7 @@
 glusterfs=""
 glusterfs_xlator_opt="no"
 glusterfs_discard="no"
+glusterfs_fallocate="no"
 glusterfs_zerofill="no"
 gtk=""
 gtkabi=""
@@ -3583,6 +3584,7 @@
       glusterfs_discard="yes"
     fi
     if $pkg_config --atleast-version=6 glusterfs-api; then
+      glusterfs_fallocate="yes"
       glusterfs_zerofill="yes"
     fi
   else
@@ -5757,6 +5759,10 @@
   echo "CONFIG_GLUSTERFS_DISCARD=y" >> $config_host_mak
 fi
 
+if test "$glusterfs_fallocate" = "yes" ; then
+  echo "CONFIG_GLUSTERFS_FALLOCATE=y" >> $config_host_mak
+fi
+
 if test "$glusterfs_zerofill" = "yes" ; then
   echo "CONFIG_GLUSTERFS_ZEROFILL=y" >> $config_host_mak
 fi