Docker: Copy Into A Container Volume

I need to copy a few files into my docker container.. Should be easy right? Turns out it's not so trivial. In Docker 1.0.0 and earlier the docker cp command can be used to copy files from a container to the host, but not the other way around...

Most of the time you can work around this by using an ADD statement in the Dockerfile but I often need to populate some data within data-only volume containers before I start other containers that use the data. To achieve copying data into the volume you can simply use tar and pipe the contents into the volume within a new container like so:
[root@localhost ~]# docker run -d -i -t -v /volumes/wpdata --name wpdata mybusybox sh 416ea2a877267f566ef8b054a836e8b6b2550b347143c4fe8ed2616e11140226 [root@localhost ~]# [root@localhost ~]# tar -c files/ | docker run -i --rm -w /volumes/wpdata/ --volumes-from wpdata mybusybox tar -xv files/ files/file8.txt files/file9.txt files/file4.txt files/file7.txt files/file1.txt files/file6.txt files/file2.txt files/file5.txt files/file10.txt files/file3.txt

So.. In the example I created a new data-only volume container named wpdata and then ran tar to pipe the contents of a directory to a new container that also used the same volumes as the original container. Not so tough, but not as easy as docker cp. I think docker cp should have this functionality sometime in the future ( issue tracker here ).