test: integ test for being able to resnapshot dirty pages ater failure

After having a failure during snapshot we're trying to do it again and
expect all the dirty pages to be snapshotted on the second attempt if it
succeeds.

Signed-off-by: Roman Kovtyukh <HelloDearGrandma@gmail.com>
Co-authored-by: Pablo Barbáchano <pablob@amazon.com>

tests/integration_tests/functional/test_snapshot_not_loosing_dirty_pages.py

@@ -0,0 +1,45 @@
+# Copyright 2020 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+# SPDX-License-Identifier: Apache-2.0
+"""Test that the no dirty pages lost in case of error during snapshot creation."""
+
+import subprocess
+import time
+from pathlib import Path
+
+
+def test_not_loosing_dirty_pages_on_snapshot_failure(uvm_plain, microvm_factory):
+    """
+    Test that in case of error during snapshot creation no dirty pages were lost.
+    """
+    vm_mem_size = 128
+    uvm = uvm_plain
+    uvm.spawn()
+    uvm.basic_config(mem_size_mib=vm_mem_size, track_dirty_pages=True)
+    uvm.add_net_iface()
+    uvm.start()
+    uvm.ssh.run("true")
+
+    chroot = Path(uvm.chroot())
+
+    # Create a large file, so we run out of space (ENOSPC) during the snapshot
+    # Assumes a Docker /srv tmpfs of 1G, derived by trial and error
+    fudge = chroot / "fudge"
+    subprocess.check_call(f"fallocate -l 550M {fudge}", shell=True)
+
+    try:
+        uvm.snapshot_diff()
+    except RuntimeError:
+        msg = "No space left on device"
+        uvm.check_log_message(msg)
+    else:
+        assert False, "This should fail"
+
+    fudge.unlink()
+
+    # Now there is enough space for it to work
+    snap2 = uvm.snapshot_diff()
+
+    vm2 = microvm_factory.build()
+    vm2.spawn()
+    vm2.restore_from_snapshot(snap2, resume=True)
+    vm2.ssh.run("true")

tools/devtool

@@ -309,7 +309,7 @@ run_devctr() {
         --rm \
         --volume /dev:/dev \
         --volume "$FC_ROOT_DIR:$CTR_FC_ROOT_DIR:z" \
-        --tmpfs /srv:exec,dev,size=32G \
+        --tmpfs /srv:exec,dev,size=1G \
         -v /boot:/boot \
         --env PYTHONDONTWRITEBYTECODE=1 \
         "$DEVCTR_IMAGE" "${ctr_args[@]}"