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, 58 insertions, 0 deletions

diff --git a/src/df.c b/src/df.c
index cac26b7fb..63c8b313c 100644
--- a/src/df.c
+++ b/src/df.c
@@ -43,6 +43,17 @@
   proper_name ("David MacKenzie"), \
   proper_name ("Paul Eggert")
 
+/* Filled with device numbers of examined file systems to avoid
+   duplicities in output.  */
+struct devlist
+{
+  dev_t dev_num;
+  struct devlist *next;
+};
+
+/* Store of already-processed device numbers.  */
+static struct devlist *devlist_head;
+
 /* If true, show even file systems with zero size or
    uninteresting types.  */
 static bool show_all_fs;
@@ -54,6 +65,12 @@ static bool show_local_fs;
    command line argument -- even if it's a dummy (automounter) entry.  */
 static bool show_listed_fs;
 
+/* If true, include rootfs in the output.  */
+static bool show_rootfs;
+
+/* The literal name of the initial root file system.  */
+static char const *ROOTFS = "rootfs";
+
 /* Human-readable options for output.  */
 static int human_output_opts;
 
@@ -589,6 +606,29 @@ excluded_fstype (const char *fstype)
   return false;
 }
 
+/* Check if the device was already examined.  */
+
+static bool
+dev_examined (char const *mount_dir, char const *devname)
+{
+  struct stat buf;
+  if (-1 == stat (mount_dir, &buf))
+    return false;
+
+  struct devlist *devlist = devlist_head;
+  for ( ; devlist; devlist = devlist->next)
+    if (devlist->dev_num == buf.st_dev)
+      return true;
+
+  /* Add the device number to the global list devlist.  */
+  devlist = xmalloc (sizeof *devlist);
+  devlist->dev_num = buf.st_dev;
+  devlist->next = devlist_head;
+  devlist_head = devlist;
+
+  return false;
+}
+
 /* Return true if N is a known integer value.  On many file systems,
    UINTMAX_MAX represents an unknown value; on AIX, UINTMAX_MAX - 1
    represents unknown.  Use a rule that works on AIX file systems, and
@@ -758,6 +798,15 @@ get_dev (char const *disk, char const *mount_point,
   if (!selected_fstype (fstype) || excluded_fstype (fstype))
     return;
 
+  if (process_all && !show_all_fs && !show_listed_fs)
+    {
+      /* No arguments nor "df -a", then check if df has to ...  */
+      if (!show_rootfs && STREQ (disk, ROOTFS))
+        return; /* ... skip rootfs: (unless -trootfs is given.  */
+      if (dev_examined (mount_point, disk))
+        return; /* ... skip duplicate entries (bind mounts).  */
+    }
+
   /* If MOUNT_POINT is NULL, then the file system is not mounted, and this
      program reports on the file system that the special file is on.
      It would be better to report on the unmounted file system,
@@ -1283,6 +1332,7 @@ main (int argc, char **argv)
           /* Accept -F as a synonym for -t for compatibility with Solaris.  */
         case 't':
           add_fs_type (optarg);
+          show_rootfs = selected_fstype (ROOTFS);
           break;
 
         case 'v':		/* For SysV compatibility.  */
@@ -1457,6 +1507,14 @@ main (int argc, char **argv)
     }
 
   IF_LINT (free (columns));
+  IF_LINT (
+    while (devlist_head)
+      {
+        struct devlist *devlist = devlist_head->next;
+        free (devlist_head);
+        devlist_head = devlist;
+      }
+    );
 
   exit (exit_status);
 }