Updated docker pull manpage to reflect ability to specify URL of registry.

Also fixed a typo in same file.

Docker-DCO-1.1-Signed-off-by: Matthew Heon <mheon@redhat.com> (github: mheon)

Conflicts:
	contrib/man/md/docker-pull.1.md
Updated CLI documentation for docker pull with notes on specifying URL

Docker-DCO-1.1-Signed-off-by: Matthew Heon <mheon@redhat.com> (github: mheon)
Error if Docker daemon starts with BTRFS graph driver and SELinux enabled

The Docker btrfs graph driver does not interact well with SELinux at present.
If btrfs mounts the same file in several locations, the same SELinux label will
be applied to all mountpoints. In the context of the graph driver, things such
as shared libraries become inaccessible to containers due to SELInux, causing
all dynamically linked applications to fail when run in a container.

Consequently, error when we detect the daemon is being run with SELinux enabled
and the btrfs driver. Documentation has been added for this behavior.

Docker-DCO-1.1-Signed-off-by: Matthew Heon <mheon@redhat.com> (github: mheon)

Conflicts:
	docker/docker.go
New implementation of /run support

This mounts a /run tmpfs into the container, with the initial contents
copies from the /run in the base image, unless NoRunFs is set in the
HostConfig.

Additionally NoRunFs is always set during a docker build, which means
any setup of /run in a Dockerfile is saved in the image to be copied
into the final /run tmpfs when a container is started.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
pkg/cgroups Add GetMounts() and GetAllSubsystems()

This lists all currently mounted cgroups and all supported cgroup
subsystems on the machine.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
libcontainer: Mount cgroups in the container

We make a tmpfs on /sys/fs/cgroups, and here we mount read-only
versions of all the host cgroups. Additionally we make symlinks
for all merged subsystems.

For any "named" cgroup, such as "name=systemd" we also mount the
subset of the cgroup where the container lives as read-write. This
means that the container can create sub-cgroups inside the container
and move tasks into those, but it can never escape from its current
position in the cgroup hierarchy.

In particular, this allows systemd to mostly work in a non-privileged
container. The only problem currently is that PrivateTmp=true fails
because systemd is not allowed to mount a new /tmp.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
Super minimal host based secrets

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
Fix invalid fd race

Sometimes I was getting:

2014/06/13 13:47:24 finalize namespace drop bounding set read /proc/1/status: bad file descriptor

This happens when applying the capabilities, and the code that
reads the current caps opens /proc/1/status and then reads some data from it.
But during this it gets a EBADFD error.

The problem is that FinalizeNamespace() closes all FDs before applying
the caps, and if a GC then happens after /proc/1/status is opened but
before reading from the fd, then an old os.File finalizer may close the
already closed-and-reused fd, wreaking havoc.

We fix this by instead of closing the FDs we mark them close-on-exec
which guarantees that they will be closed when we do the final
exec into the container.

Cherry-picked from libcontainer master.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
Report child error better (and later)

We use a unix domain socketpair instead of a pipe for the sync pipe,
which allows us to use two-way shutdown. After sending the
context we shut down the write side which lets the child know
it finished reading.

We then block on a read in the parent for the child closing the file
(ensuring we close our version of it too) to sync for when the child
is finished initializing. If the read is non-empty we assume this
is an error report and fail with an error. Otherwise we continue as
before.

This also means we're now calling back the start callback later,
meaning at that point its more likely to have succeeded, as well as
having consumed all the container resources (like volume mounts,
making it safe to e.g. unmount them when the start callback is
called).

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)