du: handle bind-mounted directory cycles gracefully

Before this change, a directory cycle induced by a bind mount
would be treated as a fatal error, i.e., probable disk corruption.
However, such cycles are relatively common, and can be detected
efficiently, so now du emits a descriptive warning and arranges
to exit nonzero.

* NEWS (Bug fixes): Mention it.
* src/du.c: Include "mountlist.h".
(di_mnt): New global set.
(di_files): Rename global from di_set, now that there are two.
(fill_mount_table): New function.
(hash_ins): Add DI_SET parameter.
(process_file): Look up each dir dev/ino pair in the new set.
(main): Allocate, initialize, and free the new set.
* tests/du/bind-mount-dir-cycle: Add a test for the fix.
* tests/Makefile.am (TESTS): Add it.
* THANKS.in: Update.
This implements the proposal in http://bugs.gnu.org/11844.
Originally reported in http://bugs.debian.org/563254 by Alan Jenkins
and more recently as http://bugzilla.redhat.com/836557

Improved by: Jim Meyering

1 files changed, 44 insertions, 0 deletions

diff --git a/tests/du/bind-mount-dir-cycle b/tests/du/bind-mount-dir-cycle
new file mode 100755
index 000000000..8f9e197f9
--- /dev/null
+++ b/tests/du/bind-mount-dir-cycle
@@ -0,0 +1,44 @@
+#!/bin/sh
+# Exercise du's new ability to handle bind-mount-induced dir cycles.
+
+# Copyright (C) 2012 Free Software Foundation, Inc.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+. "${srcdir=.}/init.sh"; path_prepend_ ../src
+print_ver_ rm
+require_root_
+
+cleanup_()
+{
+  # When you take the undesirable shortcut of making /etc/mtab a link
+  # to /proc/mounts, unmounting "$other_partition_tmpdir" would fail.
+  # So, here we unmount a/b instead.
+  umount a/b
+}
+
+mkdir -p a/b || framework_failure_
+mount --bind a a/b \
+  || skip_ "This test requires mount with a working --bind option."
+
+echo a > exp || framework_failure_
+echo "du: mount point 'a/b' already traversed" > exp-err || framework_failure_
+
+du a > out 2> err && fail=1
+sed 's/^[0-9][0-9]*	//' out > k && mv k out
+
+compare exp-err err || fail=1
+compare exp out || fail=1
+
+Exit $fail