df: fail when the mount list is required but cannot be read

* src/df.c (main): Add conditions to fail when the mount list cannot
be read: this includes the cases when a file name argument is given
and any of -a, -l, -t or -x is used.
* doc/coreutils.texi: Document the additional error conditions.
* tests/df/no-mtab-status: Add a new test.
* tests/Makefile.am: Reference the new test.
* NEWS: Mention the fix.

5 files changed, 103 insertions, 4 deletions

diff --git a/NEWS b/NEWS
index 385617e86..46d0a4131 100644
--- a/NEWS
+++ b/NEWS
@@ -2,6 +2,11 @@ GNU coreutils NEWS                                    -*- outline -*-
 
 * Noteworthy changes in release ?.? (????-??-??) [?]
 
+  df now fails when the list of mounted file systems (/etc/mtab) cannot
+  be read, yet the file system type information is needed to process
+  certain options like -a, -l, -t and -x.
+  [This bug was present in "the beginning".]
+
 
 * Noteworthy changes in release 8.18 (2012-08-12) [stable]
 
diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index 516ec7311..744b41a9f 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -10754,6 +10754,11 @@ inspect the exit status of a command like @samp{df -t ext3 -t reiserfs
 @var{dir}} to test whether @var{dir} is on a file system of type
 @samp{ext3} or @samp{reiserfs}.
 
+Since the list of file systems (@var{mtab}) is needed to determine the
+file system type, failure includes the cases when that list cannot
+be read and one or more of the options @option{-a}, @option{-l}, @option{-t}
+or @option{-x} is used together with a file name argument.
+
 
 @node du invocation
 @section @command{du}: Estimate file space usage
diff --git a/src/df.c b/src/df.c
index 4f3b56b25..9d956cd03 100644
--- a/src/df.c
+++ b/src/df.c
@@ -1100,10 +1100,19 @@ main (int argc, char **argv)
   if (mount_list == NULL)
     {
       /* Couldn't read the table of mounted file systems.
-         Fail if df was invoked with no file name arguments;
-         Otherwise, merely give a warning and proceed.  */
-      int status =          (optind < argc ? 0 : EXIT_FAILURE);
-      const char *warning = (optind < argc ? _("Warning: ") : "");
+         Fail if df was invoked with no file name arguments,
+         or when either of -a, -l, -t or -x is used with file name
+         arguments. Otherwise, merely give a warning and proceed.  */
+      int status = 0;
+      if ( ! (optind < argc)
+           || (show_all_fs
+               || show_local_fs
+               || fs_select_list != NULL
+               || fs_exclude_list != NULL))
+        {
+          status = EXIT_FAILURE;
+        }
+      const char *warning = (status == 0 ? _("Warning: ") : "");
       error (status, errno, "%s%s", warning,
              _("cannot read table of mounted file systems"));
     }
diff --git a/tests/Makefile.am b/tests/Makefile.am
index edc04b4fb..273405f59 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -376,6 +376,7 @@ TESTS =						\
   df/df-P					\
   df/unreadable					\
   df/total-unprocessed				\
+  df/no-mtab-status				\
   dd/direct					\
   dd/misc					\
   dd/nocache					\
diff --git a/tests/df/no-mtab-status b/tests/df/no-mtab-status
new file mode 100755
index 000000000..6e078541f
--- /dev/null
+++ b/tests/df/no-mtab-status
@@ -0,0 +1,79 @@
+#!/bin/sh
+# Test df's behaviour when the mount list cannot be read.
+# This test is skipped on systems that lack LD_PRELOAD support; that's fine.
+
+# 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/>.
+
+. "${srcdir=.}/init.sh"; path_prepend_ ../src
+print_ver_ df
+
+df || skip_ "df fails"
+
+# Simulate "mtab" failure.
+cat > k.c <<'EOF' || framework_failure_
+#include <stdio.h>
+#include <errno.h>
+
+struct mntent *getmntent (FILE *fp)
+{
+  /* Prove that LD_PRELOAD works. */
+  static int done = 0;
+  if (!done)
+    {
+      fclose (fopen ("x", "w"));
+      ++done;
+    }
+  /* Now simulate the failure. */
+  errno = ENOENT;
+  return NULL;
+}
+EOF
+
+# Then compile/link it:
+$CC -shared -fPIC -ldl -O2 k.c -o k.so \
+  || framework_failure_ 'failed to compile with -shared -fPIC'
+
+# Test if LD_PRELOAD works:
+LD_PRELOAD=./k.so df
+test -f x || skip_ "internal test failure: maybe LD_PRELOAD doesn't work?"
+
+# These tests are supposed to succeed:
+LD_PRELOAD=./k.so df '.' || fail=1
+LD_PRELOAD=./k.so df -i '.' || fail=1
+LD_PRELOAD=./k.so df -T '.' || fail=1
+LD_PRELOAD=./k.so df -Ti '.' || fail=1
+LD_PRELOAD=./k.so df --total '.' || fail=1
+
+# These tests are supposed to fail:
+LD_PRELOAD=./k.so df && fail=1
+LD_PRELOAD=./k.so df -i && fail=1
+LD_PRELOAD=./k.so df -T && fail=1
+LD_PRELOAD=./k.so df -Ti && fail=1
+LD_PRELOAD=./k.so df --total && fail=1
+
+LD_PRELOAD=./k.so df -a && fail=1
+LD_PRELOAD=./k.so df -a '.' && fail=1
+
+LD_PRELOAD=./k.so df -l && fail=1
+LD_PRELOAD=./k.so df -l '.' && fail=1
+
+LD_PRELOAD=./k.so df -t hello && fail=1
+LD_PRELOAD=./k.so df -t hello '.' && fail=1
+
+LD_PRELOAD=./k.so df -x hello && fail=1
+LD_PRELOAD=./k.so df -x hello '.' && fail=1
+
+Exit $fail