[Libguestfs] [PATCH] daemon: Parse /proc/mounts instead of /etc/mtab

[Richard W.M. Jones]

This is a better alternative to:
https://www.redhat.com/archives/libguestfs/2011-February/msg00006.html

Tested by running 'make check'.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
libguestfs lets you edit virtual machines.  Supports shell scripting,
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>From 61a1a2b71c4811b9d6233a43db74229b9364f0c6 Mon Sep 17 00:00:00 2001
From: Richard W.M. Jones <rjones at redhat.com>
Date: Thu, 3 Feb 2011 09:39:49 +0000
Subject: [PATCH] daemon: Parse /proc/mounts instead of /etc/mtab

Since Fedora util-linux 2.19, the %post script does:

  rm -f /etc/mtab
  ln -s /proc/mounts /etc/mtab

We are no longer running %post scripts, so this means that /etc/mtab
is a plain file in the appliance.  Usual 'mount' still updates it, but
for some reason mount.ntfs does *not* update it in Fedora 15, meaning
that you couldn't mount and then operate on NTFS partitions.

It seems better to always parse /proc/mounts (ie. what the kernel
thinks is mounted) unconditionally, rather than relying on the
capriciousness of the external mount command.

Therefore, parse /proc/mounts instead of /etc/mtab, but add a note
saying that in future we should really be parsing
/proc/self/mountinfo, but that needs a custom parser, and the format
is rather tricky:

http://lxr.linux.no/#linux+v2.6.37/Documentation/filesystems/proc.txt#L1462
---
 daemon/mount.c |    7 +++++--
 1 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/daemon/mount.c b/daemon/mount.c
index c584f81..0c990c3 100644
--- a/daemon/mount.c
+++ b/daemon/mount.c
@@ -40,9 +40,12 @@ is_root_mounted (void)
   FILE *fp;
   struct mntent *m;
 
-  fp = setmntent ("/etc/mtab", "r");
+  /* NB: Eventually we should aim to parse /proc/self/mountinfo, but
+   * that requires custom parsing code.
+   */
+  fp = setmntent ("/proc/mounts", "r");
   if (fp == NULL) {
-    perror ("/etc/mtab");
+    perror ("/proc/mounts");
     exit (EXIT_FAILURE);
   }
 
-- 
1.7.3.5