df: do not print duplicate entries and rootfs by default

* src/df.c (struct devlist): Add new struct for storing already-
examined device numbers.
(devlist_head): Add new store of the above type.
(show_rootfs): Add new global boolean to not skip rootfs.
(dev_examined): Add new function to check if the device has
already been traversed.
(get_dev): Filter out rootfs unless "-t rootfs" or the -a
option is specified. Filter out duplicate entries by calling
the above new dev_examined unless the -a option is specified.
(main): Set the show_rootfs variable appropriately when the -t
option is specified for rootfs. Free device list (guarded by
IF_LINT).
* tests/df/skip-duplicates.sh: Add test to exercise the skipping
of duplicate entries.
* tests/df/skip-rootfs.sh: Add test to exercise the skipping
of the rootfs pseudo file system.
* tests/local.mk: Add the above new tests.
* NEWS (Changes in behavior): Mention the changes.
* doc/coreutils.texi (df invocation): Document df's behavior about
skipping rootfs and duplicate entries.

Co-authored-by: Bernhard Voelker.

1 files changed, 77 insertions, 0 deletions

diff --git a/tests/df/skip-duplicates.sh b/tests/df/skip-duplicates.sh
new file mode 100755
index 000000000..2fadee428
--- /dev/null
+++ b/tests/df/skip-duplicates.sh
@@ -0,0 +1,77 @@
+#!/bin/sh
+# Test df's behavior when the mount list contains duplicate entries.
+# 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=.}/tests/init.sh"; path_prepend_ ./src
+print_ver_ df
+
+df || skip_ "df fails"
+
+# Simulate an mtab file with two entries of the same device number.
+cat > k.c <<'EOF' || framework_failure_
+#include <stdio.h>
+#include <mntent.h>
+
+struct mntent *getmntent (FILE *fp)
+{
+  /* Prove that LD_PRELOAD works. */
+  static int done = 0;
+  if (!done)
+    {
+      fclose (fopen ("x", "w"));
+      ++done;
+    }
+
+  static struct mntent mntent;
+
+  while (done++ < 3)
+    {
+      mntent.mnt_fsname = "fsname";
+      mntent.mnt_dir = "/";
+      mntent.mnt_type = "-";
+
+      return &mntent;
+    }
+  return NULL;
+}
+EOF
+
+# Then compile/link it:
+gcc --std=gnu99 -shared -fPIC -ldl -O2 k.c -o k.so \
+  || skip_ "getmntent hack does not work on this platform"
+
+# Test if LD_PRELOAD works:
+LD_PRELOAD=./k.so df
+test -f x || skip_ "internal test failure: maybe LD_PRELOAD doesn't work?"
+
+# The fake mtab file should only contain 2 entries, both
+# having the same device number; thus the output should
+# consist of a header and one entry.
+LD_PRELOAD=./k.so df >out || fail=1
+test $(wc -l <out) -eq 2 || { fail=1; cat out; }
+
+# Ensure that filtering duplicates does not affect -a processing.
+LD_PRELOAD=./k.so df -a >out || fail=1
+test $(wc -l <out) -eq 3 || { fail=1; cat out; }
+
+# Ensure that filtering duplcates does not affect
+# argument processing (now without the fake getmntent()).
+df '.' '.' >out || fail=1
+test $(wc -l <out) -eq 3 || { fail=1; cat out; }
+
+Exit $fail