btrfs: support resizing if root is mounted ro.

Resize of btrfs fails if the mount point for the file system we are trying
to resize, i.e. the root of the filesystem is read only. With this change
we use a known (currently snapper specific) rw location to work around a
flaw that blocks resizing of the ro filesystem.

LP: #1734787

1 files changed, 17 insertions, 6 deletions

diff --git a/cloudinit/util.py b/cloudinit/util.py
index df0aa5db..9976400f 100644
--- a/cloudinit/util.py
+++ b/cloudinit/util.py
@@ -2059,7 +2059,7 @@ def expand_package_list(version_fmt, pkgs):
     return pkglist
 
 
-def parse_mount_info(path, mountinfo_lines, log=LOG):
+def parse_mount_info(path, mountinfo_lines, log=LOG, get_mnt_opts=False):
     """Return the mount information for PATH given the lines from
     /proc/$$/mountinfo."""
 
@@ -2121,11 +2121,16 @@ def parse_mount_info(path, mountinfo_lines, log=LOG):
 
         match_mount_point = mount_point
         match_mount_point_elements = mount_point_elements
+        mount_options = parts[5]
 
-    if devpth and fs_type and match_mount_point:
-        return (devpth, fs_type, match_mount_point)
+    if get_mnt_opts:
+        if devpth and fs_type and match_mount_point and mount_options:
+            return (devpth, fs_type, match_mount_point, mount_options)
     else:
-        return None
+        if devpth and fs_type and match_mount_point:
+            return (devpth, fs_type, match_mount_point)
+
+    return None
 
 
 def parse_mtab(path):
@@ -2195,7 +2200,7 @@ def parse_mount(path):
     return None
 
 
-def get_mount_info(path, log=LOG):
+def get_mount_info(path, log=LOG, get_mnt_opts=False):
     # 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.
@@ -2227,7 +2232,7 @@ def get_mount_info(path, log=LOG):
     mountinfo_path = '/proc/%s/mountinfo' % os.getpid()
     if os.path.exists(mountinfo_path):
         lines = load_file(mountinfo_path).splitlines()
-        return parse_mount_info(path, lines, log)
+        return parse_mount_info(path, lines, log, get_mnt_opts)
     elif os.path.exists("/etc/mtab"):
         return parse_mtab(path)
     else:
@@ -2613,4 +2618,10 @@ def wait_for_files(flist, maxwait, naplen=.5, log_pre=""):
     return need
 
 
+def mount_is_read_write(mount_point):
+    """Check whether the given mount point is mounted rw"""
+    result = get_mount_info(mount_point, get_mnt_opts=True)
+    mount_opts = result[-1].split(',')
+    return mount_opts[0] == 'rw'
+
 # vi: ts=4 expandtab