mk-sbuild,doc/mk-sbuild.1: aufs may still be used if overlayfs isn't

available (as is the case on Debian).

debian/changelog

@@ -1,8 +1,13 @@
 ubuntu-dev-tools (0.136) UNRELEASED; urgency=low
 
+  [ Marc Deslauriers ]
   * mk-sbuild,doc/mk-sbuild.1: switch from aufs to overlayfs, as aufs is no
     longer in the Precise kernel.
 
+  [ Stefano Rivera ]
+  * mk-sbuild,doc/mk-sbuild.1: aufs may still be used if overlayfs isn't
+    available (as is the case on Debian).
+
  -- Marc Deslauriers <marc.deslauriers@ubuntu.com>  Tue, 15 Nov 2011 16:01:32 -0500
 
 ubuntu-dev-tools (0.135) unstable; urgency=low

doc/mk-sbuild.1

@@ -54,7 +54,8 @@ Currently known distros: "\fBdebian\fR" and "\fBubuntu\fR".
 .TP
 .B \-\-vg\fR=\fIVOLUME_GROUP
 Specify a volume group, and subsequently use a default \fBSCHROOT_TYPE\fR of
-"\fBlvm-snapshot\fR" rather than "\fBdirectory\fR" (via overlayfs) mounts.
+"\fBlvm-snapshot\fR" rather than "\fBdirectory\fR" (via overlayfs or
+aufs) mounts.
 .TP
 .B \-\-type\fR=\fISHROOT_TYPE
 Specify a \fBSCHROOT_TYPE\fR.  Supported values are "\fBdirectory\fR"

mk-sbuild

@@ -24,7 +24,7 @@
 # ##################################################################
 #
 # This script creates chroots designed to be used in a snapshot mode
-# (either with LVM or overlayfs) with schroot and sbuild.
+# (with LVM, btrfs, overlayfs, or aufs) with schroot and sbuild.
 # Much love to "man sbuild-setup", https://wiki.ubuntu.com/PbuilderHowto,
 # and https://help.ubuntu.com/community/SbuildLVMHowto.
 #
@@ -536,6 +536,17 @@ case "$SCHROOT_TYPE" in
     MNT=`mktemp -d -t schroot-XXXXXX`
 esac
 
+# Debian doesn't have overlayfs yet
+case "$SCHROOT_TYPE" in
+    directory|file)
+    if grep -q '\soverlayfs$' /proc/filesystems \
+            || (/sbin/modprobe -l | grep -Fq '/overlayfs.ko'); then
+        OVERLAY_FS=overlayfs
+    else
+        OVERLAY_FS=aufs
+    fi
+esac
+
 # work around apt's GPG invocation that fails without root's .gnupg directory
 sudo mkdir -p -m 0700 "$MNT"/root/.gnupg
 
@@ -619,7 +630,7 @@ EOM
     ;;
     directory|file)
         cat >> "${TEMP_SCHROOTCONF}" <<EOM
-union-type=overlayfs
+union-type=$OVERLAY_FS
 ${SCHROOT_TYPE}=CHROOT_PATH
 EOM
     ;;