On systems that supports reflinking (i.e. btrfs) this means the dummy
backend is much faster at copying files and will be sharing file data in
a CoW fashion.
On my (btrfs) system this makes "docker run ubuntu echo hello world" go
from about 3 seconds to about 1 second. Not instant, but clearly better.
cp --reflink=auto is availible since coreutils 7.5 (around 2009), so this
seems pretty ok to rely on.
cp is also better at preserving file metadata than tar, so for instance
it will copy xattrs.
This moves Driver.Size() to Differ.DiffSize(), removing the empty
implementations in devmapper and dummy, and renaming the one in aufs.
Then we fall back to a container.Changes() implementation in the non-aufs
case.
We place the actual image/containers in the "rootfs" directory, which
allows us to have other data in the toplevel directory in the mount.
For starters, this means the "lost+found" directory from mkfs will
not always be in your container/image.
Secondly, we can create a file "id" in the toplevel dir which is not
visible from the container. This is useful because it allows us to map
back from the device fs to the container if something goes wrong with
the devicemapper metadata.
It makes no sense to use the aufs or devicemapper drivers for volumes.
The aufs one is perhaps not a big problem, but the devicemapper one
certainly is. It will be unnecessarily using a dm
blockdevice-over-loopback with a limited size base FS.
This just hardcodes the driver to be the dummy, perhaps in the future
we can have other drivers that make sense for the volumes.
This adds a generic Status call in the Driver api and
implements if for the devicemapper backend.
The status is an array of key/value strings rather than a map so that
we can guarantee some static order of the docker info output.
This adds 3 tests:
Verify that ChangesDirs() returns nothing when run on a copy of the
same directory.
Verify that various mutations of a directory get reported with the
right changes.
Verify that ExportChanges() + ApplyLayer() of the above mutation gets
an identical directory.
Unfortunately the last test is disabled because it fails in multiple
ways atm. But I want to get it in so that we can fix it.
For people who toggle drivers we want to save the driver used
to create a container so that if the driver changes we can skip
loading the container and it should not show up in docker ps
Victor Vieux