Recover mysql-upgrade dir/link handlig wrongly removed in f7caa04

The preinst is supposed to save possible mysql datadir link
and the postinst is supposed to recover it.

Also unify namig of the variables that reference the data
and log directories.

debian/mariadb-server-10.0.lintian-overrides

@@ -1,9 +1,9 @@
 # OK, embedded has same source
 mariadb-server-10.0: embedded-library usr/bin/mysqlbinlog: libmysqlclient
 # ash's buildin has no "-e" so use /bin/echo
-mariadb-server-10.0: command-with-path-in-maintainer-script postinst:156 /bin/echo
-mariadb-server-10.0: command-with-path-in-maintainer-script postinst:166 /bin/echo
-mariadb-server-10.0: command-with-path-in-maintainer-script postinst:179 /bin/echo
+mariadb-server-10.0: command-with-path-in-maintainer-script postinst:199 /bin/echo
+mariadb-server-10.0: command-with-path-in-maintainer-script postinst:209 /bin/echo
+mariadb-server-10.0: command-with-path-in-maintainer-script postinst:222 /bin/echo
 # OK, path /usr/sbin/invoke-rc.d is only used in check, executes are run without the path
 mariadb-server-10.0: command-with-path-in-maintainer-script postinst:17 /usr/sbin/invoke-rc.d
 mariadb-server-10.0: command-with-path-in-maintainer-script postrm:15 /usr/sbin/invoke-rc.d

debian/mariadb-server-10.0.postinst

@@ -73,6 +73,49 @@ case "$1" in
     mysql_cfgdir=/etc/mysql
     mysql_upgradedir=/var/lib/mysql-upgrade
 
+    # If the following symlink exists, it is a preserved copy the old data dir
+    # created by the preinst script during a upgrade that would have otherwise
+    # been replaced by an empty mysql dir.  This should restore it.
+    for dir in DATADIR LOGDIR; do
+
+      if [ "$dir" = "DATADIR" ]; then
+        targetdir=$mysql_datadir
+      else
+        targetdir=$mysql_logdir
+      fi
+
+      savelink="$mysql_upgradedir/$dir.link"
+      if [ -L "$savelink" ]; then
+        # If the targetdir was a symlink before we upgraded it is supposed
+        # to be either still be present or not existing anymore now.
+        if [ -L "$targetdir" ]; then
+          rm "$savelink"
+        elif [ ! -d "$targetdir" ]; then
+          mv "$savelink" "$targetdir"
+        else
+          # this should never even happen, but just in case...
+          mysql_tmp=`mktemp -d -t mysql-symlink-restore-XXXXXX`
+          echo "this is very strange!  see $mysql_tmp/README..." >&2
+          mv "$targetdir" "$mysql_tmp"
+          cat << EOF > "$mysql_tmp/README"
+
+Ff you're reading this, it's most likely because you had replaced /var/lib/mysql
+with a symlink, then upgraded to a new version of mysql, and then dpkg
+removed your symlink (see #182747 and others). The mysql packages noticed
+that this happened, and as a workaround have restored it. However, because
+/var/lib/mysql seems to have been re-created in the meantime, and because
+e don't want to rm -rf something we don't know as much about, we are going
+to leave this unexpected directory here. If your database looks normal,
+and this is not a symlink to your database, you should be able to blow
+this all away.
+
+EOF
+        fi
+      fi
+	    rmdir $mysql_upgradedir 2>/dev/null || true
+
+    done
+
     # Ensure the existence and right permissions for the database and
     # log files.
     if [ ! -d "$mysql_statedir" -a ! -L "$mysql_statedir" ]; then mkdir "$mysql_statedir"; fi

debian/mariadb-server-10.0.preinst

@@ -14,9 +14,8 @@ ${DEBIAN_SCRIPT_TRACE:+ echo "#42#DEBUG# RUNNING $0 $*" 1>&2 }
 
 export PATH=$PATH:/sbin:/usr/sbin:/bin:/usr/bin
 MYADMIN="/usr/bin/mysqladmin --defaults-file=/etc/mysql/debian.cnf"
-DATADIR=/var/lib/mysql
-LOGDIR=/var/log/mysql
-UPGRADEDIR=/var/lib/mysql-upgrade
+mysql_datadir=/var/lib/mysql
+mysql_upgradedir=/var/lib/mysql-upgrade
 
 # Try to stop the server in a sane way. If it does not success let the admin
 # do it himself. No database directories should be removed while the server
@@ -50,7 +49,7 @@ this_version=10.0
 
 # Show upgrade warning if old data exists
 # Designed for scenarios where users upgrade form MySQL 5.5 or 5.6 or MariaDB 5.5
-for i in `ls $DATADIR/debian-*.flag 2>/dev/null`; do
+for i in `ls $mysql_datadir/debian-*.flag 2>/dev/null`; do
   found_version=`echo $i | sed 's/.*debian-\([0-9\.]\+\).flag/\1/'`
   if dpkg --compare-versions "$this_version" '>>' "$found_version"; then
     db_fset mariadb-server/oneway_migration seen false || true
@@ -69,7 +68,7 @@ done
 
 # Safe the user from stupidities.
 show_downgrade_warning=0
-for i in `ls $DATADIR/debian-*.flag 2>/dev/null`; do
+for i in `ls $mysql_datadir/debian-*.flag 2>/dev/null`; do
   found_version=`echo $i | sed 's/.*debian-\([0-9\.]\+\).flag/\1/'`
   if dpkg --compare-versions "$this_version" '<<' "$found_version"; then
     show_downgrade_warning=1
@@ -82,11 +81,11 @@ if [ "$show_downgrade_warning" = 1 ]; then
   db_go
   db_get mariadb-server-$this_version/really_downgrade || true
   if [ "$RET" = "true" ]; then
-    rm -f $DATADIR/debian-*.flag
+    rm -f $mysql_datadir/debian-*.flag
   else
     echo "Aborting downgrade from (at least) $found_version to $this_version." 1>&2
     echo "If are sure you want to downgrade to $this_version, remove the file" 1>&2
-    echo "$DATADIR/debian-*.flag and try installing again." 1>&2
+    echo "$mysql_datadir/debian-*.flag and try installing again." 1>&2
     db_stop
     exit 1
   fi
@@ -140,19 +139,19 @@ set -e
 for dir in DATADIR LOGDIR; do
     checkdir=`eval echo "$"$dir`
     if [ -L "$checkdir" ]; then
-	mkdir -p "$UPGRADEDIR"
-	cp -dT "$checkdir" "$UPGRADEDIR/$dir.link"
+	mkdir -p "$mysql_upgradedir"
+	cp -dT "$checkdir" "$mysql_upgradedir/$dir.link"
     fi
 done
 
 # creating mysql home directory
-if [ ! -d $DATADIR -a ! -L $DATADIR ]; then
- 	mkdir $DATADIR
+if [ ! -d $mysql_datadir -a ! -L $mysql_datadir ]; then
+ 	mkdir $mysql_datadir
 fi
 
 # checking disc space
-if LC_ALL=C BLOCKSIZE= df --portability $DATADIR/. | tail -n 1 | awk '{ exit ($4>1000) }'; then
-  echo "ERROR: There's not enough space in $DATADIR/" 1>&2
+if LC_ALL=C BLOCKSIZE= df --portability $mysql_datadir/. | tail -n 1 | awk '{ exit ($4>1000) }'; then
+  echo "ERROR: There's not enough space in $mysql_datadir/" 1>&2
   db_stop
   exit 1
 fi
@@ -165,8 +164,8 @@ fi
 # The "set +e" is necessary as e.g. a ".journal" of a ext3 partition is
 # not chgrp'able (#318435).
 set +e
-chown mysql:mysql $DATADIR
-find $DATADIR -follow -not -group mysql -print0 2>/dev/null \
+chown mysql:mysql $mysql_datadir
+find $mysql_datadir -follow -not -group mysql -print0 2>/dev/null \
   | xargs -0 --no-run-if-empty chgrp mysql
 set -e