fix issue with get_mount_info on older kernels

This removes the requirement for /proc/PID/mountinfo, which was added in linux
kernel 2.6.26.  We could potentially re-visit this and read /proc/mounts rather
than /proc/mtab, but mtab proves effective in testing.

LP: #1248625

2 files changed, 16 insertions, 2 deletions

diff --git a/ChangeLog b/ChangeLog
index ca856e6b..33f43530 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -8,6 +8,8 @@
  - support apt-add-archive with 'cloud-archive:' format.  (LP: #1244355)
  - Change SmartOS verb for availability zone (LP: #1249124)
  - documentation fix for boothooks to use 'cloud-init-per'
+ - fix resizefs module by supporting kernels that do not have
+   /proc/PID/mountinfo.  (LP: #1248625) [Tim Daly Jr.]
 0.7.3:
  - fix omnibus chef installer (LP: #1182265) [Chris Wing]
  - small fix for OVF datasource for iso transport on non-iso9660 filesystem
diff --git a/cloudinit/util.py b/cloudinit/util.py
index 9e6e0a73..a8ddb390 100644
--- a/cloudinit/util.py
+++ b/cloudinit/util.py
@@ -1737,6 +1737,15 @@ def parse_mount_info(path, mountinfo_lines, log=LOG):
         return None
 
 
+def parse_mtab(path):
+    """On older kernels there's no /proc/$$/mountinfo, so use mtab."""
+    for line in load_file("/etc/mtab").splitlines():
+        devpth, mount_point, fs_type = line.split()[:3]
+        if mount_point == path:
+            return devpth, fs_type, mount_point
+    return None
+
+
 def get_mount_info(path, log=LOG):
     # Use /proc/$$/mountinfo to find the device where path is mounted.
     # This is done because with a btrfs filesystem using os.stat(path)
@@ -1767,8 +1776,11 @@ def get_mount_info(path, log=LOG):
     # So use /proc/$$/mountinfo to find the device underlying the
     # input path.
     mountinfo_path = '/proc/%s/mountinfo' % os.getpid()
-    lines = load_file(mountinfo_path).splitlines()
-    return parse_mount_info(path, lines, log)
+    if os.path.exists(mountinfo_path):
+        lines = load_file(mountinfo_path).splitlines()
+        return parse_mount_info(path, lines, log)
+    else:
+        return parse_mtab(path)
 
 
 def which(program):