Add support for "compose exec"

Add support to run shell commands inside a checked out
ostree branch.

The way that this works is the following:

1. Determine the branch to checkout.
2. Checkout the branch in the workspace.
3. Use systemd-nspawn to create a shell inside
   the branch.

Test Plan
PASSED Installed apt-ostree from git repo.
PASSED Run sudo apt-ostree compose create \
           --base config/debian/bookworm \
           --repo /repo debian/bookworm \
           bookworm-test
PASSED Run sudo apt-ostree compose exec --repo /repo --branch
       bookwork-test "cat /etc/debian_version"

Story: 2010867
Task: 48556

Change-Id: I6ff9658fc04ec83d50d2cb5f3b8dbb70e3065688
Signed-off-by: Charles Short <charles.short@windriver.com>

apt_ostree/cmd/compose/__init__.py

@@ -15,6 +15,7 @@ from apt_ostree.cmd.compose.init import init
 from apt_ostree.cmd.compose.install import install
 from apt_ostree.cmd.compose.repo import repo
 from apt_ostree.cmd.compose.restore import restore
+from apt_ostree.cmd.compose.run import run
 from apt_ostree.cmd.compose.uninstall import uninstall
 from apt_ostree.cmd.compose.upgrade import upgrade
 
@@ -34,4 +35,5 @@ compose.add_command(install)
 compose.add_command(upgrade)
 compose.add_command(repo)
 compose.add_command(restore)
+compose.add_command(run)
 compose.add_command(uninstall)

apt_ostree/cmd/compose/run.py

@@ -0,0 +1,54 @@
+"""
+Copyright (c) 2023 Wind River Systems, Inc.
+
+SPDX-License-Identifier: Apache-2.0
+
+"""
+
+import errno
+import sys
+
+import click
+
+from apt_ostree.cmd import pass_state_context
+from apt_ostree.run import RunCommand
+
+
+@click.command(
+    name="exec",
+    help="Run a command or shell from an Ostree branch.")
+@pass_state_context
+@click.option(
+    "--mounts",
+    help="Path to yaml configuration for mount points.",
+    type=click.Path(exists=True)
+)
+@click.option(
+    "--root",
+    help="Path to operate on",
+)
+@click.option(
+    "--pre-exec",
+    'pre_exec',
+    help="Run the command before executing the container",
+)
+@click.argument(
+    "cmd",
+    # If command not specified then execute a shell.
+    default=""
+)
+def run(state,
+        mounts,
+        root,
+        pre_exec,
+        cmd):
+    try:
+        RunCommand(state).run_command(cmd, mounts, pre_exec, root)
+    except KeyboardInterrupt:
+        click.secho("\n" + ("Exiting at your request."))
+        sys.exit(130)
+    except BrokenPipeError:
+        sys.exit()
+    except OSError as error:
+        if error.errno == errno.ENOSPC:
+            sys.exit("error - No space left on device.")

apt_ostree/run.py

@@ -0,0 +1,53 @@
+"""
+Copyright (c) 2023 Wind River Systems, Inc.
+
+SPDX-License-Identifier: Apache-2.0
+
+"""
+
+import os
+import sys
+
+import click
+from rich.console import Console
+import yaml
+
+from apt_ostree import utils
+
+
+class RunCommand:
+    def __init__(self, state):
+        self.state = state
+        self.console = Console()
+
+    def run_command(self, command, mount_points, pre_exec, rootfs):
+        """Run a command in an ostree branch."""
+        if not os.path.exists(rootfs):
+            click.secho(f"Directory not found: {rootfs}", fg="red")
+            sys.exit(1)
+
+        mounts = None
+        if mount_points:
+            self.console.print("Loading configuration.")
+            with open(mount_points, "r") as f:
+                mounts = yaml.safe_load(f)
+
+        if pre_exec:
+            self.console.print(f"Executing pre-command: {pre_exec}",
+                               highlight=False)
+            cmd = ["systemd-nspawn", "-q", "-D", rootfs]
+            cmd += pre_exec.split()
+            r = utils.run_command(cmd)
+            if r.returncode != 0:
+                self.console.print("Sucessfully executed pre-command")
+
+        # Run the systemd-nspawn command.
+        cmd = ["systemd-nspawn", "-q"]
+        if mounts:
+            for m in mounts:
+                cmd += (["--bind", f"{m}"])
+        cmd += ["-D", rootfs]
+        if len(command) != 0:
+            cmd += command.split()
+
+        utils.run_command(cmd, check=False)

etc/mounts.yaml

@@ -0,0 +1,3 @@
+# example configuration for apt-ostree compose exec
+---
+- /var/www/html/repo:/ostree