df: also deduplicate virtual file systems

* src/df.c (filter_mountlist): Remove the constraint that
a '/' needs to be in the device name for a mount entry to
be considered for deduplication.  Virtual file systems also
have storage associated with them (like tmpfs for example),
and thus need to be deduplicated since they will be shown
in the default df output and subject to --total processing also.
* test/df/skip-duplicates.sh: Add a test to ensure we deduplicate
all entries, even for virtual file systems.  Also avoid possible
length operations on many remote file systems in the initial
check of df operation.  Also avoid the assumption that "/root"
is on the same file system as "/".
* NEWS: Mention the change in behavior.

1 files changed, 34 insertions, 13 deletions

diff --git a/tests/df/skip-duplicates.sh b/tests/df/skip-duplicates.sh
index 266520aa6..d872f27fc 100755
--- a/tests/df/skip-duplicates.sh
+++ b/tests/df/skip-duplicates.sh
@@ -21,19 +21,28 @@
 print_ver_ df
 require_gcc_shared_
 
-df || skip_ "df fails"
+# We use --local here so as to not activate
+# potentially very many remote mounts.
+df --local || skip_ "df fails"
 
-# Simulate an mtab file with two entries of the same device number.
-# Also add entries with unstatable mount dirs to ensure that's handled.
+export CU_NONROOT_FS=$(df --local --output=target 2>&1 | grep /. | head -n1)
+test -z "$CU_NONROOT_FS" && unique_entries=1 || unique_entries=2
+
+# Simulate an mtab file to test various cases.
 cat > k.c <<'EOF' || framework_failure_
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 #include <mntent.h>
 
+#define STREQ(a, b) (strcmp (a, b) == 0)
+
 struct mntent *getmntent (FILE *fp)
 {
+  static char *nonroot_fs;
+  static int done;
+
   /* Prove that LD_PRELOAD works. */
-  static int done = 0;
   if (!done)
     {
       fclose (fopen ("x", "w"));
@@ -43,18 +52,30 @@ struct mntent *getmntent (FILE *fp)
   static struct mntent mntents[] = {
     {.mnt_fsname="/short",  .mnt_dir="/invalid/mount/dir"},
     {.mnt_fsname="fsname",  .mnt_dir="/",},
-    {.mnt_fsname="/fsname", .mnt_dir="/root"},
+    {.mnt_fsname="/fsname", .mnt_dir="/."},
     {.mnt_fsname="/fsname", .mnt_dir="/"},
+    {.mnt_fsname="virtfs",  .mnt_dir="/NONROOT"},
+    {.mnt_fsname="virtfs",  .mnt_dir="/NONROOT"},
   };
 
-  if (!getenv ("CU_TEST_DUPE_INVALID") && done == 1)
+  if (done == 1)
+    {
+      nonroot_fs = getenv ("CU_NONROOT_FS");
+      if (!nonroot_fs || !*nonroot_fs)
+        nonroot_fs = "/"; /* merge into / entries.  */
+    }
+
+  if (done == 1 && !getenv ("CU_TEST_DUPE_INVALID"))
     done++;  /* skip the first entry.  */
 
-  while (done++ <= 4)
+  while (done++ <= 6)
     {
       mntents[done-2].mnt_type = "-";
+      if (STREQ (mntents[done-2].mnt_dir, "/NONROOT"))
+        mntents[done-2].mnt_dir = nonroot_fs;
       return &mntents[done-2];
     }
+
   return NULL;
 }
 EOF
@@ -69,22 +90,22 @@ test -f x || skip_ "internal test failure: maybe LD_PRELOAD doesn't work?"
 
 # The fake mtab file should only contain entries
 # having the same device number; thus the output should
-# consist of a header and one entry.
+# consist of a header and unique entries.
 LD_PRELOAD=./k.so df >out || fail=1
-test $(wc -l <out) -eq 2 || { fail=1; cat out; }
+test $(wc -l <out) -eq $(expr 1 + $unique_entries) || { fail=1; cat out; }
 
 # Ensure we fail when unable to stat invalid entries
 LD_PRELOAD=./k.so CU_TEST_DUPE_INVALID=1 df >out && fail=1
-test $(wc -l <out) -eq 2 || { fail=1; cat out; }
+test $(wc -l <out) -eq $(expr 1 + $unique_entries) || { fail=1; cat out; }
 
 # df should also prefer "/fsname" over "fsname"
 test $(grep -c '/fsname' <out) -eq 1 || { fail=1; cat out; }
-# ... and "/fsname" with '/' as Mounted on over '/root'
-test $(grep -c '/root' <out) -eq 0 || { fail=1; cat out; }
+# ... and "/fsname" with '/' as Mounted on over '/.'
+test $(grep -cF '/.' <out) -eq 0 || { 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 4 || { fail=1; cat out; }
+test $(wc -l <out) -eq 6 || { fail=1; cat out; }
 
 # Ensure that filtering duplicates does not affect
 # argument processing (now without the fake getmntent()).