[PATCH] df: use open(2) to trigger automounting

[Tomáš Smetana]

Hello,
  there is a problem with df when run on an automounted volume:

$ df /misc/test; df /misc/test
Filesystem           1K-blocks      Used Available Use% Mounted on
-                            0         0         0   -  /misc
Filesystem           1K-blocks      Used Available Use% Mounted on
/tmp                  15013664   7302844   6935860  52% /misc/test

The /misc/test is an automounted filesystem and as you can see the first run
did not trigger the automount.  According to Ian Kent (autofs maintainer), an
indirect map that uses the browse option won't trigger mounts for system
calls such as stat(2), statfs(2) etc. to avoid mount storms when using such
things as colour ls.  He also suggested to use some other call before stat(2)
to make df automount the filesytem.  The following patch is a paraphrase of
his suggestion rewritten according to Jim Meyering's instructions.

---
From 4c064d1b4cc0666bdc5835a72ddf6018f08b4c2c Mon Sep 17 00:00:00 2001
From: Tomas Smetana <address@hidden>
Date: Tue, 28 Apr 2009 11:21:49 +0200
Subject: [PATCH] df: use open(2) to trigger automounting

---
 src/df.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/src/df.c b/src/df.c
index 7b8a082..9daa398 100644
--- a/src/df.c
+++ b/src/df.c
@@ -993,12 +993,16 @@ main (int argc, char **argv)
       stats = xnmalloc (argc - optind, sizeof *stats);
       for (i = optind; i < argc; ++i)
        {
-         if (stat (argv[i], &stats[i - optind]))
+          int fd;
+         if ((fd = open(argv[i], O_RDONLY | O_NOCTTY)) < 0
+                  || fstat (fd, &stats[i - optind]))
            {
              error (0, errno, "%s", quote (argv[i]));
              exit_status = EXIT_FAILURE;
              argv[i] = NULL;
            }
+          if (0 <= fd)
+              close(fd);
        }
     }
 
-- 
1.6.0.6