Add overlayfs graph backend

This backend uses the overlayfs union filesystem for containers
plus hard link file sharing for images.

Each container/image can have a "root" subdirectory which is a plain
filesystem hierarchy, or they can use overlayfs.

If they use overlayfs there is a "upper" directory and a "lower-id"
file, as well as "merged" and "work" directories. The "upper"
directory has the upper layer of the overlay, and "lower-id" contains
the id of the parent whose "root" directory shall be used as the lower
layer in the overlay. The overlay itself is mounted in the "merged"
directory, and the "work" dir is needed for overlayfs to work.

When a overlay layer is created there are two cases, either the
parent has a "root" dir, then we start out with a empty "upper"
directory overlaid on the parents root. This is typically the
case with the init layer of a container which is based on an image.
If there is no "root" in the parent, we inherit the lower-id from
the parent and start by making a copy if the parents "upper" dir.
This is typically the case for a container layer which copies
its parent -init upper layer.

Additionally we also have a custom implementation of ApplyLayer
which makes a recursive copy of the parent "root" layer using
hardlinks to share file data, and then applies the layer on top
of that. This means all chile images share file (but not directory)
data with the parent.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
Make test-unit runnable without parallel

Signed-off-by: Yohei Ueda <yohei@jp.ibm.com>
Export envvars necessary for unit-test

Signed-off-by: Yohei Ueda <yohei@jp.ibm.com>
handle GET redirects

Signed-off-by: Victor Vieux <vieux@docker.com>
fix unix socket

Signed-off-by: Victor Vieux <vieux@docker.com>
Allow IPC namespace to be shared between containers or with the host

Some workloads rely on IPC for communications with other processes.  We
would like to split workloads between two container but still allow them
to communicate though shared IPC.

This patch mimics the --net code to allow --ipc=host to not split off
the IPC Namespace.  ipc=container:CONTAINERID to share ipc between containers

If you share IPC between containers, then you need to make sure SELinux labels
match.

Docker-DCO-1.1-Signed-off-by: Dan Walsh <dwalsh@redhat.com> (github: rhatdan)
update timeout

Signed-off-by: Victor Vieux <vieux@docker.com>
Merge pull request #8999 from yoheiueda/test-unit-without-parallel

Make test-unit runnable without parallel
Merge pull request #9074 from rhatdan/shm

Allow IPC namespace to be shared between containers or with the host
use _, _ string

Signed-off-by: Victor Vieux <vieux@docker.com>
Merge pull request #9108 from vieux/handle_redirects

handle GET redirects over HTTP
Merge pull request #7619 from alexlarsson/overlayfs

Add overlayfs graph backend