[PATCH][blivet][rhel7.1-branch] Improve format handling for lvm snapshots.

[Vojtěch Trefný]

Non-existent lvm snapshots have a copy of the origin's format as their
format. When an origin's format changes, all non-existent snapshots of
that origin must have their formats updated as well.

Related: rhbz#1236988

(cherry picked from commit 1c2d8a0b3633145b0528c4a0734e4ac7a7bffed8)

Signed-off-by: Vojtech Trefny 
---
 blivet/devices.py | 47 ++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 36 insertions(+), 11 deletions(-)

diff --git a/blivet/devices.py b/blivet/devices.py
index c576a19..b389e31 100644
--- a/blivet/devices.py
+++ b/blivet/devices.py
@@ -3027,6 +3027,10 @@ class LVMLogicalVolumeDevice(DMDevice):
                     raise ValueError("constructor requires a LVMVolumeGroupDevice instance")
             elif not isinstance(parents, LVMVolumeGroupDevice):
                 raise ValueError("constructor requires a LVMVolumeGroupDevice instance")
+
+        # When this device's format is set in the superclass constructor it will
+        # try to access self.snapshots.
+        self.snapshots = []
         DMDevice.__init__(self, name, size=size, fmt=fmt,
                           sysfsPath=sysfsPath, parents=parents,
                           exists=exists)
@@ -3036,7 +3040,6 @@ class LVMLogicalVolumeDevice(DMDevice):
         self.logSize = logSize
         self.metaDataSize = 0
         self.segType = segType or "linear"
-        self.snapshots = []

self.req_grow = None
         self.req_max_size = Size(0)
@@ -3107,6 +3110,11 @@ class LVMLogicalVolumeDevice(DMDevice):
         return (self.vg.align(self.size, roundup=True) * self.copies
                 + self.logSize + self.metaDataSize)

+    def _setFormat(self, fmt):
+        super(LVMLogicalVolumeDevice, self)._setFormat(fmt)
+        for snapshot in (s for s in self.snapshots if not s.exists):
+            snapshot._updateFormatFromOrigin()
+
     @property
     def vg(self):
         """ This Logical Volume's Volume Group. """
@@ -3337,8 +3345,8 @@ class LVMSnapShotBase(object):
         Normal/old snapshots must be removed with their origin, while thin
         snapshots can remain after their origin is removed.

-        It is also impossible to set the format for a snapshot explicitly as it
-        always has the same format as its origin.
+        It is also impossible to set the format for a non-existent snapshot
+        explicitly as it always has the same format as its origin.
     """
     __metaclass__ = abc.ABCMeta

@@ -3383,15 +3391,32 @@ class LVMSnapShotBase(object):
         if vorigin and not exists:
             raise ValueError("only existing vorigin snapshots are supported")

-    def _setFormat(self, fmt):
-        pass
+    def _updateFormatFromOrigin(self):
+        """ Update the snapshot's format to reflect the origin's.
+            .. note::
+                This should only be called for non-existent snapshot devices.
+                Once a snapshot exists its format is distinct from that of its
+                origin.

-    def _getFormat(self):
-        if self.origin is None:
-            fmt = getFormat(None)
+        """
+        fmt = copy.deepcopy(self.origin.format)
+        fmt.exists = False
+        if hasattr(fmt, "mountpoint"):
+            fmt.mountpoint = ""
+            fmt._chrootedMountpoint = None
+            fmt.device = self.path # pylint: disable=no-member
+
+        super(LVMSnapShotBase, self)._setFormat(fmt)
+
+    def _setFormat(self, fmt):
+        # If a snapshot exists it can have a format that is distinct from its
+        # origin's. If it does not exist its format must be a copy of its
+        # origin's.
+        if self.exists: # pylint: disable=no-member
+            super(LVMSnapShotBase, self)._setFormat(fmt)
         else:
-            fmt = self.origin.format
-        return fmt
+            log.info("copying %s origin's format", self.name) # pylint: disable=no-member
+            self._updateFormatFromOrigin()

@abc.abstractmethod
     def _create(self):
@@ -3736,7 +3761,7 @@ class LVMThinSnapShotDevice(LVMSnapShotBase, LVMThinLogicalVolumeDevice):

LVMSnapShotBase.__init__(self, origin=origin, exists=exists)
         LVMThinLogicalVolumeDevice.__init__(self, name, parents=parents,
-                                            sysfsPath=sysfsPath,fmt=None,
+                                            sysfsPath=sysfsPath,fmt=fmt,
                                             segType=segType,
                                             uuid=uuid, size=size, exists=exists)

[Jiří Konečný]

On Thu, 2015-07-09 at 12:56 +0200, Vojtech Trefny wrote:
> Non-existent lvm snapshots have a copy of the origin's format as 
> their
> format. When an origin's format changes, all non-existent snapshots 
> of
> that origin must have their formats updated as well.
>
> Related: rhbz#1236988

Ack.