refactor get_mount_info and add tests

1) Refactor util.get_mount_info() to facilitate unit testing.
2) Add unit tests for /proc/$$/mountinfo parsing.

1 files changed, 54 insertions, 34 deletions

diff --git a/cloudinit/util.py b/cloudinit/util.py
index 709d5cca..a1f6e004 100644
--- a/cloudinit/util.py
+++ b/cloudinit/util.py
@@ -1576,44 +1576,29 @@ def expand_package_list(version_fmt, pkgs):
     return pkglist
 
 
-def get_mount_info(path, log=LOG):
-    # Use /proc/$$/mountinfo to find the device where path is mounted.
-    # This is done because with a btrfs filesystem using os.stat(path)
-    # does not return the ID of the device.
-    #
-    # Here, / has a device of 18 (decimal).
-    #
-    # $ stat /
-    #   File: '/'
-    #   Size: 234               Blocks: 0          IO Block: 4096   directory
-    # Device: 12h/18d   Inode: 256         Links: 1
-    # Access: (0755/drwxr-xr-x)  Uid: (    0/    root)   Gid: (    0/    root)
-    # Access: 2013-01-13 07:31:04.358011255 +0000
-    # Modify: 2013-01-13 18:48:25.930011255 +0000
-    # Change: 2013-01-13 18:48:25.930011255 +0000
-    #  Birth: -
-    #
-    # Find where / is mounted:
-    #
-    # $ mount | grep ' / '
-    # /dev/vda1 on / type btrfs (rw,subvol=@,compress=lzo)
-    #
-    # And the device ID for /dev/vda1 is not 18:
-    #
-    # $ ls -l /dev/vda1
-    # brw-rw---- 1 root disk 253, 1 Jan 13 08:29 /dev/vda1
-    #
-    # So use /proc/$$/mountinfo to find the device underlying the
-    # input path.
+def parse_mount_info(path, mountinfo_lines, log=LOG):
+    """Return the mount information for PATH given the lines from
+    /proc/$$/mountinfo."""
+
     path_elements = [e for e in path.split('/') if e]
     devpth = None
     fs_type = None
     match_mount_point = None
     match_mount_point_elements = None
-    mountinfo_path = '/proc/%s/mountinfo' % os.getpid()
-    for line in load_file(mountinfo_path).splitlines():
+    for i, line in enumerate(mountinfo_lines):
         parts = line.split()
 
+        # Completely fail if there is anything in any line that is
+        # unexpected, as continuing to parse past a bad line could
+        # cause an incorrect result to be returned, so it's better
+        # return nothing than an incorrect result.
+
+        # The minimum number of elements in a valid line is 10.
+        if len(parts) < 10:
+            log.debug("Line %d has two few columns (%d): %s",
+                      i + 1, len(parts), line)
+            return None
+
         mount_point = parts[4]
         mount_point_elements = [e for e in mount_point.split('/') if e]
 
@@ -1638,8 +1623,8 @@ def get_mount_info(path, log=LOG):
         try:
             i = parts.index('-')
         except ValueError:
-            log.debug("Did not find column named '-' in %s",
-                      mountinfo_path)
+            log.debug("Did not find column named '-' in line %d: %s",
+                      i + 1, line)
             return None
 
         # Get the path to the device.
@@ -1647,7 +1632,8 @@ def get_mount_info(path, log=LOG):
             fs_type = parts[i + 1]
             devpth = parts[i + 2]
         except IndexError:
-            log.debug("Too few columns in %s after '-' column", mountinfo_path)
+            log.debug("Too few columns after '-' column in line %d: %s",
+                      i + 1, line)
             return None
 
         match_mount_point = mount_point
@@ -1657,3 +1643,37 @@ def get_mount_info(path, log=LOG):
         return (devpth, fs_type, match_mount_point)
     else:
         return None
+
+
+def get_mount_info(path, log=LOG):
+    # Use /proc/$$/mountinfo to find the device where path is mounted.
+    # This is done because with a btrfs filesystem using os.stat(path)
+    # does not return the ID of the device.
+    #
+    # Here, / has a device of 18 (decimal).
+    #
+    # $ stat /
+    #   File: '/'
+    #   Size: 234               Blocks: 0          IO Block: 4096   directory
+    # Device: 12h/18d   Inode: 256         Links: 1
+    # Access: (0755/drwxr-xr-x)  Uid: (    0/    root)   Gid: (    0/    root)
+    # Access: 2013-01-13 07:31:04.358011255 +0000
+    # Modify: 2013-01-13 18:48:25.930011255 +0000
+    # Change: 2013-01-13 18:48:25.930011255 +0000
+    #  Birth: -
+    #
+    # Find where / is mounted:
+    #
+    # $ mount | grep ' / '
+    # /dev/vda1 on / type btrfs (rw,subvol=@,compress=lzo)
+    #
+    # And the device ID for /dev/vda1 is not 18:
+    #
+    # $ ls -l /dev/vda1
+    # brw-rw---- 1 root disk 253, 1 Jan 13 08:29 /dev/vda1
+    #
+    # So use /proc/$$/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)