df: ignore non file system entries in /proc/mounts

Linux with network namespaces contains entries in /proc/mounts like:
  proc net:[4026532464] proc rw,nosuid,nodev,noexec,relatime 0 0
resulting in a failure to stat 'net:[...]', inducing a warning
and an exit with failure status.

* src/df.c (get_dev): Ignore all relative mount points.
* tests/df/skip-duplicates.sh: Add an entry to test relative dirs.

2 files changed, 7 insertions, 1 deletions

diff --git a/src/df.c b/src/df.c
index 24897a33f..a7fc57ff7 100644
--- a/src/df.c
+++ b/src/df.c
@@ -853,6 +853,11 @@ get_dev (char const *disk, char const *mount_point, char const* file,
   if (!selected_fstype (fstype) || excluded_fstype (fstype))
     return;
 
+  /* Ignore relative MOUNT_POINTs, which are present for example
+     in /proc/mounts on Linux with network namespaces.  */
+  if (!force_fsu && mount_point && ! IS_ABSOLUTE_FILE_NAME (mount_point))
+    return;
+
   /* 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,
diff --git a/tests/df/skip-duplicates.sh b/tests/df/skip-duplicates.sh
index d872f27fc..44f7d4ca7 100755
--- a/tests/df/skip-duplicates.sh
+++ b/tests/df/skip-duplicates.sh
@@ -56,6 +56,7 @@ struct mntent *getmntent (FILE *fp)
     {.mnt_fsname="/fsname", .mnt_dir="/"},
     {.mnt_fsname="virtfs",  .mnt_dir="/NONROOT"},
     {.mnt_fsname="virtfs",  .mnt_dir="/NONROOT"},
+    {.mnt_fsname="netns",   .mnt_dir="net:[1234567]"},
   };
 
   if (done == 1)
@@ -68,7 +69,7 @@ struct mntent *getmntent (FILE *fp)
   if (done == 1 && !getenv ("CU_TEST_DUPE_INVALID"))
     done++;  /* skip the first entry.  */
 
-  while (done++ <= 6)
+  while (done++ <= 7)
     {
       mntents[done-2].mnt_type = "-";
       if (STREQ (mntents[done-2].mnt_dir, "/NONROOT"))