dpkg-maintscript-helper: Fix symlink_to_dir and dir_to_symlink commands

- Always run postinst code regardless of prior-version, as the package
  might have been never configured before.
- Be more strict when checking the expected state of paths.
- Rename subcommand shell code to check-files-ownership.
- Change dir_to_symlink switch code to use a staging empty directory,
  to avoid dpkg removing files from other packages, when removing the
  package old files during upgrade.
- Bump minimal version in man page to 1.17.5.

Closes: #731730

debian/changelog

@@ -9,6 +9,16 @@ dpkg (1.17.5) UNRELEASED; urgency=low
   * Fix segfault in update-alternatives when adding or renaming slaves for
     an existing alternative. Regression introduced in dpkg 1.17.2.
     Closes: #731710
+  * Fix dpkg-maintscript-helper symlink_to_dir and dir_to_symlink commands:
+    - Always run postinst code regardless of prior-version, as the package
+      might have been never configured before.
+    - Be more strict when checking the expected state of paths.
+    - Rename subcommand shell code to check-files-ownership.
+    - Change dir_to_symlink switch code to use a staging empty directory,
+      to avoid dpkg removing files from other packages, when removing the
+      package old files during upgrade.
+    - Bump minimal version in man page to 1.17.5.
+    Closes: #731730
 
   [ Updated dpkg translations ]
   * German (Sven Joachim).

man/dpkg-maintscript-helper.1

@@ -15,7 +15,7 @@
 .\" You should have received a copy of the GNU General Public License
 .\" along with this program.  If not, see <https://www.gnu.org/licenses/>.
 .
-.TH dpkg\-maintscript\-helper 1 "2012-05-04" "Debian Project" "dpkg suite"
+.TH dpkg\-maintscript\-helper 1 "2013-12-11" "Debian Project" "dpkg suite"
 .SH NAME
 dpkg\-maintscript\-helper \- works around known dpkg limitations in maintainer scripts
 .
@@ -197,9 +197,15 @@ of the new symlink at \fIpathname\fP.
 Current implementation: the \fBpreinst\fP checks if the directory
 exists, does not contain conffiles, pathnames owned by other packages,
 or locally created pathnames, if not then it's left in place, otherwise
-it's renamed to \fIpathname\fP\fB.dpkg\-backup\fP. On configuration,
-the \fBpostinst\fP removes \fIpathname\fP\fB.dpkg\-backup\fP if
-\fIpathname\fP\fB.dpkg\-backup\fP is still a directory. On
+it's renamed to \fIpathname\fP\fB.dpkg\-backup\fP, and an empty staging
+directory named \fIpathname\fP is created, marked with a file so that
+dpkg can track it. On configuration, the \fBpostinst\fP finishes the
+switch if \fIpathname\fP\fB.dpkg\-backup\fP is still a directory and
+\fIpathname\fP is the staging directory; it removes the staging directory
+mark file, moves the newly created files inside the staging directory
+to the symlink target \fInew-target\fP/, replaces the now empty staging
+directory \fIpathname\fP with a symlink to \fInew-target\fP, and
+removes \fIpathname\fP\fB.dpkg\-backup\fP. On
 abort\-upgrade/abort\-install, the \fBpostrm\fP renames
 \fIpathname\fP\fB.dpkg\-backup\fP back to \fIpathname\fP if required.
 .
@@ -210,9 +216,9 @@ using it unconditionally requires a pre-dependency to ensure that the
 required version of \fBdpkg\fP has been unpacked before. The required version
 depends on the command used, for \fBrm_conffile\fP and \fBmv_conffile\fP
 it is 1.15.7.2, for \fBsymlink_to_dir\fP and \fBdir_to_symlink\fP
-it is 1.17.2:
+it is 1.17.5:
 .P
-    \fBPre\-Depends:\fP dpkg (>= 1.17.2)
+    \fBPre\-Depends:\fP dpkg (>= 1.17.5)
 .P
 But in many cases the operation done by the program is not critical for
 the package, and instead of using a pre-dependency we can call the

scripts/dpkg-maintscript-helper.sh

@@ -1,6 +1,6 @@
 #!/bin/sh
 #
-# Copyright © 2007,2011-2012 Guillem Jover <guillem@debian.org>
+# Copyright © 2007,2011-2013 Guillem Jover <guillem@debian.org>
 # Copyright © 2010 Raphaël Hertzog <hertzog@debian.org>
 # Copyright © 2008 Joey Hess <joeyh@debian.org>
 # Copyright © 2005 Scott James Remnant (original implementation on www.dpkg.org)
@@ -272,8 +272,13 @@ symlink_to_dir() {
 		fi
 		;;
 	postinst)
+		# We cannot bail depending on the version, as here we only
+		# know what was the last configured version, and we might
+		# have been unpacked, then upgraded with an unpack and thus
+		# never been configured before.
 		if [ "$1" = "configure" ] && [ -h "${SYMLINK}.dpkg-backup" ] &&
-		    dpkg --compare-versions "$2" le-nl "$LASTVERSION"; then
+		   [ "$(readlink -f ${SYMLINK}.dpkg-backup)" = "$SYMLINK_TARGET" ]
+		then
 			rm -f "${SYMLINK}.dpkg-backup"
 		fi
 		;;
@@ -283,7 +288,8 @@ symlink_to_dir() {
 		fi
 		if [ "$1" = "abort-install" -o "$1" = "abort-upgrade" ] &&
 		   [ -n "$2" ] &&
-		   [ -h "${SYMLINK}.dpkg-backup" ] && [ ! -e "$SYMLINK" ] &&
+		   [ ! -e "$SYMLINK" ] && [ -h "${SYMLINK}.dpkg-backup" ] &&
+		   [ "$(readlink -f ${SYMLINK}.dpkg-backup)" = "$SYMLINK_TARGET" ] &&
 		   dpkg --compare-versions "$2" le-nl "$LASTVERSION"; then
 			echo "Restoring backup of $SYMLINK ..."
 			mv "${SYMLINK}.dpkg-backup" "$SYMLINK"
@@ -333,21 +339,22 @@ dir_to_symlink() {
 	case "$DPKG_MAINTSCRIPT_NAME" in
 	preinst)
 		if [ "$1" = "install" -o "$1" = "upgrade" ] &&
-		   [ -n "$2" ] && [ -d "$PATHNAME" ] &&
+		   [ -n "$2" ] &&
+		   [ ! -h "$PATHNAME" ] && [ -d "$PATHNAME" ] &&
 		   dpkg --compare-versions "$2" le-nl "$LASTVERSION"; then
 			prepare_dir_to_symlink "$PACKAGE" "$PATHNAME"
 		fi
 		;;
 	postinst)
+		# We cannot bail depending on the version, as here we only
+		# know what was the last configured version, and we might
+		# have been unpacked, then upgraded with an unpack and thus
+		# never been configured before.
 		if [ "$1" = "configure" ] &&
-		   [ -d "${PATHNAME}.dpkg-backup" ] && [ -h "$PATHNAME" ] &&
-		   [ "$(readlink -f $PATHNAME)" = "$SYMLINK_TARGET" ] &&
-		    dpkg --compare-versions "$2" le-nl "$LASTVERSION"; then
-			# By now, dpkg will have updated the symlink to point
-			# to the new location, but we are left behind the old
-			# files owned by this package in the backup directory,
-			# just remove it.
-			rm -rf "${PATHNAME}.dpkg-backup"
+		   [ -d "${PATHNAME}.dpkg-backup" ] &&
+		   [ ! -h "$PATHNAME" ] && [ -d "$PATHNAME" ] &&
+		   [ -f "$PATHNAME/.dpkg-staging-dir" ]; then
+			finish_dir_to_symlink "$PATHNAME" "$SYMLINK_TARGET"
 		fi
 		;;
 	postrm)
@@ -356,12 +363,13 @@ dir_to_symlink() {
 		fi
 		if [ "$1" = "abort-install" -o "$1" = "abort-upgrade" ] &&
 		   [ -n "$2" ] &&
-		   [ -d "${PATHNAME}.dpkg-backup" ] && [ -h "$PATHNAME" ] &&
-		   [ "$(readlink -f $PATHNAME)" = "$SYMLINK_TARGET" ] &&
+		   [ -d "${PATHNAME}.dpkg-backup" ] &&
+		   [ \( ! -h "$PATHNAME" -a -d "$PATHNAME" -a \
+		        -f "$PATHNAME/.dpkg-staging-dir" \) -o \
+		     \( -h "$PATHNAME" -a \
+		        "$(readlink -f $PATHNAME)" = "$SYMLINK_TARGET" \) ] &&
 		   dpkg --compare-versions "$2" le-nl "$LASTVERSION"; then
-			echo "Restoring backup of $PATHNAME ..."
-			rm -f "$PATHNAME"
-			mv "${PATHNAME}.dpkg-backup" "$PATHNAME"
+			abort_dir_to_symlink "$PATHNAME"
 		fi
 		;;
 	*)
@@ -391,17 +399,69 @@ prepare_dir_to_symlink()
 			return 1
 		fi
 		return 0
-	' subcommand "$PACKAGE" || \
+	' check-files-ownership "$PACKAGE" || \
 		error "directory '$PATHNAME' contains files not owned by" \
 		      "package $PACKAGE, cannot switch to symlink"
 
-	# Move the directory aside and make a temporary symlink to reduce the
-	# time the contents are not available. dpkg will not be able to remove
-	# the old files from the backup directory after unpack, because it
-	# will have updated the symlink to point to the new location already,
-	# we'll remove them ourselves later on.
+	# At this point, we know that the directory either contains no files,
+	# or only non-conffiles owned by the package.
+	#
+	# To do the switch we cannot simply replace it with the final symlink
+	# just yet, because dpkg needs to remove any file present in the old
+	# package that have disappeared in the new one, and we do not want to
+	# lose files resolving to the same pathname in the symlink target.
+	#
+	# We cannot replace the directory with a staging symlink either,
+	# because dpkg will update symlinks to their new target.
+	#
+	# So we need to create a staging directory, to avoid removing files
+	# from other packages, and to trap any new files in the directory
+	# to move them to their correct place later on.
 	mv -f "$PATHNAME" "${PATHNAME}.dpkg-backup"
-	ln -s "${PATHNAME}.dpkg-backup" "$PATHNAME"
+	mkdir "$PATHNAME"
+
+	# Mark it as a staging directory, so that we can track things.
+	touch "$PATHNAME/.dpkg-staging-dir"
+}
+
+finish_dir_to_symlink()
+{
+	local PATHNAME="$1"
+	local SYMLINK_TARGET="$2"
+
+	# Move the contents of the staging directory to the symlink target,
+	# as those are all new files installed between this package being
+	# unpacked and configured.
+	rm "$PATHNAME/.dpkg-staging-dir"
+	find "$PATHNAME" -mindepth 1 -print0 | \
+		xargs -0 -i% mv -f "%" "$SYMLINK_TARGET/"
+
+	# Remove the staging directory.
+	rmdir "$PATHNAME"
+
+	# Do the actual switch.
+	ln -s "$SYMLINK_TARGET" "$PATHNAME"
+
+	# We are left behind the old files owned by this package in the backup
+	# directory, just remove it.
+	rm -rf "${PATHNAME}.dpkg-backup"
+}
+
+abort_dir_to_symlink()
+{
+	local PATHNAME="$1"
+
+	echo "Restoring backup of $PATHNAME ..."
+	if [ -h "$PATHNAME" ]; then
+		rm -f "$PATHNAME"
+	else
+		# The staging directory must be empty, as no other package
+		# should have been unpacked inbetween.
+		rm -f "$PATHNAME/.dpkg-staging-dir"
+		rmdir "$PATHNAME"
+	fi
+
+	mv "${PATHNAME}.dpkg-backup" "$PATHNAME"
 }
 
 # Common functions