[lxc-devel] [PATCH] lxc-clone: support 'permanent ephemeral' containers

[Serge Hallyn]

All of this needs a rewrite/redesign, and that will be coming (details
below), but for now

You can start 'non-ephemeral ephemeral' containers using

	lxc-start-ephemeral -o oldname -n newname --keep-data

When you shut that down, the container stick around and can be
restarted.  Now lxc-clone will recognize such a container by the
presence of the delta0/ which contains the read-write overlayfs
layer.  This means you can do incremental development of containers,
i.e.

	lxc-create -t ubuntu -n r1
	lxc-start-ephemeral --keep-data -o r1 -n r1-2
	# make some changes, poweroff
	lxc-clone -o r1-2 -n r1-3
	# make some changes...
	lxc-clone -o r1-3 -n r1-4
	# etc...

Now, as for design changes...  from a higher level

	1. lxc-clone should be re-written in c and exported through the
	   api.
	2. lxc-clone should support overlayfs and aufs
	3. lxc-start-ephemeral should become a thin layer which clones a
	   container, starts and stops and destroys it.

at a lower level,

	1. the api should support container->setup_mounts
	2. lxc-clone should be written as a set of backend classes which
	   can copy mounts to each other.  So when you load a container
	   which is lvm-backed, it creates a lvm backend class.  That
	   class instance can be converted into a loopback or qemu-nbd
	   or directory backed class.  A directory-backed class can be
	   converted into a overlayfs or aufs backed class, which (a)
	   uses the dirctory-backed class as the read-only base, and (b)
	   pins the base container (so it can't be deleted until all
	   snapshots are deleted).

Signed-off-by: Serge Hallyn <serge.hallyn at ubuntu.com>
---
 src/lxc/lxc-clone.in | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/src/lxc/lxc-clone.in b/src/lxc/lxc-clone.in
index 291db30..4c8acb4 100755
--- a/src/lxc/lxc-clone.in
+++ b/src/lxc/lxc-clone.in
@@ -251,6 +251,23 @@ elif which btrfs >/dev/null 2>&1 && btrfs subvolume list $oldroot >/dev/null 2>&
     # if oldroot is a btrfs subvolume, assume they want a snapshot
     btrfs subvolume snapshot "$oldroot" "$rootfs" 2>&1 || { echo "$(basename $0): btrfs snapshot failed" >&2; false; }
     echo "lxc.rootfs = $rootfs" >> "$lxc_path/$lxc_new/config"
+elif [ -d $lxc_path/$lxc_orig/delta0 ]; then # this is a quasi-ephemeral container
+    if [ $container_running = "True" ]; then
+        echo "$(basename $0): container $lxc_orig is running." >&2
+        cleanup
+    fi
+    rsync -Hax $lxc_path/$lxc_orig/delta0 $lxc_path/$lxc_new/
+    touch $lxc_path/$lxc_new/configured
+    cp -f $lxc_path/$lxc_orig/pre-mount $lxc_path/$lxc_new/
+    sed -i "s@$lxc_path/$lxc_orig@$lxc_path/$lxc_new at g" $lxc_path/$lxc_new/config
+    sed -i "s@$lxc_path/$lxc_orig@$lxc_path/$lxc_new at g" $lxc_path/$lxc_new/pre-mount
+    sed -i "s at LXC_NAME=\"$lxc_orig at LXC_NAME=\"$lxc_new@" $lxc_path/$lxc_new/pre-mount
+    # lxc-start-ephemeral will have updated /etc/hostname and such under the
+    # delta0, so just mounting the delta should suffice.
+    mkdir -p $rootfs
+    mount --bind $lxc_path/$lxc_new/delta0 $rootfs
+    mounted=1
+    echo "lxc.rootfs = $rootfs" >> "$lxc_path/$lxc_new/config"
 else
     if [ $snapshot = "yes" ]; then
         echo "$(basename $0): cannot snapshot a directory" >&2
-- 
1.8.1.2