Currently if a mount point is not accessible by the calling user,

invalid information will be printed if the -t flag is specified.

$ df -t ufs
Filesystem  1K-blocks     Used    Avail Capacity  Mounted on
/dev/ad0s1a    495726   139944   316124    31%    /
/dev/ad0s1e    253678     6438   226946     3%    /tmp
/dev/ad0s1f  56206340 13594248 38115586    26%    /usr
/dev/ad0s1d    694126    19812   618784     3%    /var
/dev/ad0s1d    694126    19812   618784     3%    /var
$

Note that the mount point which is not accessible shows
up as the previous file system that was printed. The reason
for this is that df -t will call statfs(2) on the pathname
supplied by getfsstat(2).

This is done to refresh the file system statistics in the
event that a previous file system had a long delay in
providing its stats.

This change affects the df utility in the following ways:
o Teach df has to deal with statfs(2) failing. If statfs(2)
  fails, fall back on the possibly stale stats provided by
  the initial call to getfsstat(2).
o Print a warning that the fs stats could possibly be stale
o Modify the man page and document this new behavior
  as a bug.

Approved by:	bmilekic (mentor)
PR:		68165

bin/df/df.1

@@ -149,7 +149,9 @@ is set, the block counts will be displayed in units of that size block.
 .Sh BUGS
 The
 .Fl n
-flag is ignored if a file or file system is specified.
+flag is ignored if a file or file system is specified. Also, if a mount
+point is not accessible by the user, it is possible that the file system
+information could be stale.
 .Sh SEE ALSO
 .Xr lsvfs 1 ,
 .Xr quota 1 ,

bin/df/df.c

@@ -298,7 +298,7 @@ getmntpt(const char *name)
 static size_t
 regetmntinfo(struct statfs **mntbufp, long mntsize, const char **vfslist)
 {
-	int i, j;
+	int error, i, j;
 	struct statfs *mntbuf;
 
 	if (vfslist == NULL)
@@ -308,10 +308,20 @@ regetmntinfo(struct statfs **mntbufp, long mntsize, const char **vfslist)
 	for (j = 0, i = 0; i < mntsize; i++) {
 		if (checkvfsname(mntbuf[i].f_fstypename, vfslist))
 			continue;
-		if (!nflag)
-			(void)statfs(mntbuf[i].f_mntonname,&mntbuf[j]);
-		else if (i != j)
-			mntbuf[j] = mntbuf[i];
+		/*
+		 * XXX statfs(2) can fail for various reasons. It may be
+		 * possible that the user does not have access to the
+		 * pathname, if this happens, we will fall back on
+		 * "stale" filesystem statistics.
+		 */
+		error = statfs(mntbuf[i].f_mntonname, &mntbuf[j]);
+		if (nflag || error < 0)
+			if (i != j) {
+				if (error < 0)
+					warnx("%s stats possibly stale",
+					    mntbuf[i].f_mntonname);
+				mntbuf[j] = mntbuf[i];
+			}
 		j++;
 	}
 	return (j);