xen-tools: add eve-enter-container script

Once terminal is attached to the Vm console which hosts a container
user can execute `eve-enter-container` script and enter corresponding
container.

Script uses `nsenter -t $pid` and pid is extracted from the
/mnt/entrypoint-pid file, created by the chroot2 utility.

Signed-off-by: Roman Penyaev <[email protected]>

pkg/xen-tools/Dockerfile

@@ -12,6 +12,7 @@ COPY initrd/init-initrd initrd/mount_disk.sh initrd/udhcpc_script.sh /
 COPY initrd/poweroff /sbin/poweroff
 COPY initrd/chroot2.c initrd/hacf.c /tmp/
 COPY initrd/00000080 /etc/acpi/PWRF/
+COPY initrd/eve-enter-container /bin/
 RUN gcc -s -o /chroot2 /tmp/chroot2.c
 RUN gcc -s -o /hacf /tmp/hacf.c
 RUN mkinitfs -n -F base -i /init-initrd -o /runx-initrd

pkg/xen-tools/initrd/base.files

@@ -1,4 +1,5 @@
 /bin/busybox
+/bin/eve-enter-container
 /sbin/agetty
 /sbin/mke2fs
 /lib/libext2fs.so.2*

pkg/xen-tools/initrd/eve-enter-container

@@ -0,0 +1,13 @@
+#!/bin/sh
+
+# PID of the started entrypoint container process.
+# PID file is created from the `init-initrd` script.
+PID_FILE="/mnt/entrypoint-pid"
+
+if [ ! -f "$PID_FILE" ]; then
+    echo "Error: PID file '$PID_FILE' not found. Container did not start?"
+    exit 1
+fi
+
+PID=$(cat "$PID_FILE")
+nsenter -t "$PID" -m -u -i -n -p -r/mnt/rootfs -w/mnt/rootfs