tests/docker/docker.py: add update operation

This adds a new operation to the docker script to allow updating of
binaries in an existing container. This is because it would be
inefficient to re-build the whole container just for an update to the
QEMU binary.

To update the executable run:

    ./tests/docker/docker.py update \
        debian:armhf ./arm-linux-user/qemu-arm

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 1468934445-32183-6-git-send-email-famz@redhat.com
Signed-off-by: Fam Zheng <famz@redhat.com>

tests/docker/docker.py

@@ -21,6 +21,8 @@ import uuid
 import argparse
 import tempfile
 import re
+from tarfile import TarFile, TarInfo
+from StringIO import StringIO
 from shutil import copy, rmtree
 
 def _text_checksum(text):
@@ -94,9 +96,11 @@ class Docker(object):
         self._instances = []
         atexit.register(self._kill_instances)
 
-    def _do(self, cmd, quiet=True, **kwargs):
+    def _do(self, cmd, quiet=True, infile=None, **kwargs):
         if quiet:
             kwargs["stdout"] = subprocess.PIPE
+        if infile:
+            kwargs["stdin"] = infile
         return subprocess.call(self._command + cmd, **kwargs)
 
     def _do_kill_instances(self, only_known, only_active=True):
@@ -152,6 +156,11 @@ class Docker(object):
                  [docker_dir],
                  quiet=quiet)
 
+    def update_image(self, tag, tarball, quiet=True):
+        "Update a tagged image using "
+
+        self._do(["build", "-t", tag, "-"], quiet=quiet, infile=tarball)
+
     def image_matches_dockerfile(self, tag, dockerfile):
         try:
             checksum = self.get_image_dockerfile_checksum(tag)
@@ -245,6 +254,54 @@ class BuildCommand(SubCommand):
 
         return 0
 
+class UpdateCommand(SubCommand):
+    """ Update a docker image with new executables. Arguments: <tag> <executable>"""
+    name = "update"
+    def args(self, parser):
+        parser.add_argument("tag",
+                            help="Image Tag")
+        parser.add_argument("executable",
+                            help="Executable to copy")
+
+    def run(self, args, argv):
+        # Create a temporary tarball with our whole build context and
+        # dockerfile for the update
+        tmp = tempfile.NamedTemporaryFile(suffix="dckr.tar.gz")
+        tmp_tar = TarFile(fileobj=tmp, mode='w')
+
+        # Add the executable to the tarball
+        bn = os.path.basename(args.executable)
+        ff = "/usr/bin/%s" % bn
+        tmp_tar.add(args.executable, arcname=ff)
+
+        # Add any associated libraries
+        libs = _get_so_libs(args.executable)
+        if libs:
+            for l in libs:
+                tmp_tar.add(os.path.realpath(l), arcname=l)
+
+        # Create a Docker buildfile
+        df = StringIO()
+        df.write("FROM %s\n" % args.tag)
+        df.write("ADD . /\n")
+        df.seek(0)
+
+        df_tar = TarInfo(name="Dockerfile")
+        df_tar.size = len(df.buf)
+        tmp_tar.addfile(df_tar, fileobj=df)
+
+        tmp_tar.close()
+
+        # reset the file pointers
+        tmp.flush()
+        tmp.seek(0)
+
+        # Run the build with our tarball context
+        dkr = Docker()
+        dkr.update_image(args.tag, tmp, quiet=args.quiet)
+
+        return 0
+
 class CleanCommand(SubCommand):
     """Clean up docker instances"""
     name = "clean"