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, 6 insertions, 0 deletions

diff --git a/NEWS b/NEWS
index f04c5100e..0e1414c44 100644
--- a/NEWS
+++ b/NEWS
@@ -43,6 +43,12 @@ GNU coreutils NEWS                                    -*- outline -*-
   field can be in any column.  If there is no source column, then df
   prints 'total' into the target column.
 
+  df now properly outputs file system information with bind mounts present on
+  the system by skipping duplicate entries (identified by the device number).
+
+  df now skips the early-boot pseudo file system type "rootfs" unless either
+  the -a option or "-t rootfs" is specified.
+
   nl no longer supports the --page-increment option which was deprecated
   since coreutils-7.5.  Use --line-increment instead.