docker: add wrapper for detecting storage driver and bump to 1.4

The new dockerd wrapper script does its best to select between the btrfs
and overlay backends based on the filesystem mounted at /var/lib/docker.

The new 1.4 version will remain marked as ~amd64 for testing purposes
until we stabilize its dependencies, including Linux 3.18.x.

sdk_container/src/third_party/coreos-overlay/app-emulation/docker/docker-1.4.0.ebuild

@@ -0,0 +1 @@
+docker-9999.ebuild

sdk_container/src/third_party/coreos-overlay/app-emulation/docker/docker-9999.ebuild

@@ -28,6 +28,7 @@ IUSE="aufs +btrfs contrib +device-mapper doc lxc vim-syntax zsh-completion"
 
 # https://github.com/docker/docker/blob/master/hack/PACKAGERS.md#build-dependencies
 CDEPEND="
+	>=sys-kernel/coreos-kernel-3.18.0
 	>=dev-db/sqlite-3.7.9:3
 	device-mapper? (
 		>=sys-fs/lvm2-2.02.89[thin]
@@ -186,6 +187,9 @@ src_install() {
 	newinitd contrib/init/openrc/docker.initd docker
 	newconfd contrib/init/openrc/docker.confd docker
 
+	exeinto /usr/lib/coreos
+	doexe "${FILESDIR}/dockerd"
+
 	systemd_newunit "${FILESDIR}/docker.service-r1" "docker.service"
 	systemd_dounit "${FILESDIR}/docker.socket"
 	systemd_newunit "${FILESDIR}/early-docker.service-r1" "early-docker.service"

sdk_container/src/third_party/coreos-overlay/app-emulation/docker/files/docker.service-r1

@@ -6,12 +6,11 @@ Requires=docker.socket early-docker.target
 
 [Service]
 Environment=TMPDIR=/var/tmp
-Environment=DOCKER_DRIVER=btrfs
 Environment=DOCKER_OPTS='--insecure-registry="0.0.0.0/0"'
 EnvironmentFile=-/run/docker_opts.env
 LimitNOFILE=1048576
 LimitNPROC=1048576
-ExecStart=/usr/bin/docker --daemon --host=fd:// $DOCKER_OPTS
+ExecStart=/usr/lib/coreos/dockerd --daemon --host=fd:// $DOCKER_OPTS
 
 [Install]
 WantedBy=multi-user.target

sdk_container/src/third_party/coreos-overlay/app-emulation/docker/files/dockerd

@@ -0,0 +1,67 @@
+#!/bin/bash
+# Wrapper for launching docker daemons with an appropriate backend.
+
+set -e
+
+parse_docker_args() {
+    local flag value
+    while [[ $# -gt 0 ]]; do
+        flag="$1"
+        shift
+
+        # treat --flag=foo and --flag foo identically
+        if [[ "${flag}" == *=* ]]; then
+            flag="${flag%=*}"
+            set -- "${flag#*=}" "$@"
+        fi
+
+        case "${flag}" in
+            -g|--graph)
+                ARG_ROOT="$1"
+                shift
+                ;;
+            -s|--storage-driver)
+                ARG_DRIVER="$1"
+                shift
+                ;;
+            *)
+                # ignore everything else
+                ;;
+        esac
+    done
+}
+
+select_docker_driver() {
+    local fstype
+
+    # mimic docker's behavior to ensure we stat the right filesystem.
+    if [[ -L "${ARG_ROOT}" ]]; then
+        ARG_ROOT="$(readlink -f "${ARG_ROOT}")"
+    fi
+
+    mkdir --parents --mode=0700 "${ARG_ROOT}"
+    fstype=$(findmnt --noheadings --output FSTYPE --target "${ARG_ROOT}")
+
+    case "${fstype}" in
+        btrfs)
+            export DOCKER_DRIVER=btrfs
+            ;;
+        ext4|tmpfs) # As of 3.18
+            export DOCKER_DRIVER=overlay
+            ;;
+        *)
+            # Fall back to whatever docker's default behavior is.
+            ;;
+    esac
+}
+
+ARG_ROOT="/var/lib/docker"
+ARG_DRIVER=""
+parse_docker_args "$@"
+
+# Do not override the driver if it is already explicitly configured.
+if [[ -z "${ARG_DRIVER}" && -z "${DOCKER_DRIVER}" ]]; then
+    select_docker_driver
+fi
+
+exec docker "$@"

sdk_container/src/third_party/coreos-overlay/app-emulation/docker/files/early-docker.service-r1

@@ -6,10 +6,9 @@ Requires=early-docker.socket
 
 [Service]
 Environment=TMPDIR=/var/tmp
-Environment=DOCKER_DRIVER=btrfs
 LimitNOFILE=1048576
 LimitNPROC=1048576
-ExecStart=/usr/bin/docker --daemon --host=fd:// --bridge=none --iptables=false --ip-masq=false --graph=/var/lib/early-docker --pidfile=/var/run/early-docker.pid
+ExecStart=/usr/lib/coreos/dockerd --daemon --host=fd:// --bridge=none --iptables=false --ip-masq=false --graph=/var/lib/early-docker --pidfile=/var/run/early-docker.pid
 
 [Install]
 WantedBy=early-docker.target