Merge branch 'master' into joeyconfig

1 files changed, 33 insertions, 0 deletions

diff --git a/src/Propellor/Property/Chroot.hs b/src/Propellor/Property/Chroot.hs
index 01cd4d3e..ad2ae705 100644
--- a/src/Propellor/Property/Chroot.hs
+++ b/src/Propellor/Property/Chroot.hs
@@ -11,6 +11,7 @@ module Propellor.Property.Chroot (
 	ChrootTarball(..),
 	noServices,
 	inChroot,
+	exposeTrueLocaldir,
 	-- * Internal use
 	provisioned',
 	propagateChrootInfo,
@@ -295,6 +296,38 @@ setInChroot h = h { hostInfo = hostInfo h `addInfo` InfoVal (InChroot True) }
 newtype InChroot = InChroot Bool
 	deriving (Typeable, Show)
 
+-- | Runs an action with the true localdir exposed,
+-- not the one bind-mounted into a chroot. The action is passed the
+-- path containing the contents of the localdir outside the chroot.
+--
+-- In a chroot, this is accomplished by temporily bind mounting the localdir
+-- to a temp directory, to preserve access to the original bind mount. Then
+-- we unmount the localdir to expose the true localdir. Finally, to cleanup,
+-- the temp directory is bind mounted back to the localdir.
+exposeTrueLocaldir :: (FilePath -> Propellor a) -> Propellor a
+exposeTrueLocaldir a = ifM inChroot
+	( withTmpDirIn (takeDirectory localdir) "propellor.tmp" $ \tmpdir ->
+		bracket_
+			(movebindmount localdir tmpdir)
+			(movebindmount tmpdir localdir)
+			(a tmpdir)
+	, a localdir
+	)
+  where
+	movebindmount from to = liftIO $ do
+		run "mount" [Param "--bind", File from, File to]
+		-- Have to lazy unmount, because the propellor process
+		-- is running in the localdir that it's unmounting..
+		run "umount" [Param "-l", File from]
+		-- We were in the old localdir; move to the new one after
+		-- flipping the bind mounts. Otherwise, commands that try
+		-- to access the cwd will fail because it got umounted out
+		-- from under.
+		changeWorkingDirectory "/"
+		changeWorkingDirectory localdir
+	run cmd ps = unlessM (boolSystem cmd ps) $
+		error $ "exposeTrueLocaldir failed to run " ++ show (cmd, ps)
+
 -- | Generates a Chroot that has all the properties of a Host.
 -- 
 -- Note that it's possible to create loops using this, where a host