Add support for running image-garden as a snap

The new image-garden snap offers a one-stop-shop for integration
testing, bundling qemu, spread and image-garden build recipes.

Extend the documentation, the run-spread.sh helper script as well as
spread.yaml to support this new method.

Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@canonical.com>

README.md

@@ -214,6 +214,18 @@ in an ephemeral virtual machine. This allows testing in isolation from the
 host, as well as testing across different commonly used distributions and their
 real kernels.
 
+Image Garden is available as a snap. If you wish to use it this way then snap
+then install the snap with:
+
+```sh
+sudo snap install image-garden
+```
+
+If you need to install snapd first, see https://snapcraft.io/docs/installing-snapd
+
+Alternatively you may build image-garden and spread from source, and install
+dependencies manually.
+
 ```sh
 sudo apt install git golang whois ovmf genisoimage qemu-utils qemu-system
 go install github.com/snapcore/spread/cmd/spread@latest
@@ -227,8 +239,9 @@ git clean -xdf
 # or ~/go/bin/spread -v garden:ubuntu-cloud-24.04:tests/regression/apparmor:at_secure
 ```
 
-Running the `run_spread.sh` script, with `spread` on `PATH` will run all the
-tests across several supported systems (Debian, Ubuntu and openSUSE).
+Running the `run_spread.sh` script, with `image-garden` snap installed or with
+`spread` on `PATH` will run all the tests across several supported systems
+(Debian, Ubuntu and openSUSE).
 
 If you include a `bzImage` file in the root of the repository then that kernel
 will be used in the integration test. Please look at `spread.yaml` for details.

run-spread.sh

@@ -4,14 +4,24 @@
 # quad-core CPU with 8GB of RAM and no desktop session.
 set -xeu
 
-if test -z "$(command -v spread)"; then
+if [ -n "$(command -v image-garden.spread)" ]; then
+	if ! snap run --shell image-garden -c "snapctl is-connected kvm"; then
+		echo "Please connect the kvm interface to image-garden" >&2
+		echo "snap connect image-garden:kvm" >&2
+		exit 1
+	fi
+	SPREAD=image-garden.spread
+else
+	SPREAD=spread
+	if test -z "$(command -v spread)"; then
 		echo "You need to install spread from https://github.com/snapcore/spread with the Go compiler and the command: go install github.com/snapcore/spread/cmd/spread@latest" >&2
 		exit 1
-fi
+	fi
 
-if test -z "$(command -v image-garden)"; then
+	if test -z "$(command -v image-garden)"; then
 		echo "You need to install image-garden from https://gitlab.com/zygoon/image-garden: make install prefix=/usr/local" >&2
 		exit 1
+	fi
 fi
 
 rm -rf spread-logs spread-artifacts
@@ -23,7 +33,7 @@ for system in \
 	ubuntu-cloud-22.04 \
 	ubuntu-cloud-24.04 \
 	ubuntu-cloud-24.10; do
-	if ! spread -artifacts ./spread-artifacts -v "$system" | tee spread-logs/"$system".log; then
+	if ! "$SPREAD" -artifacts ./spread-artifacts -v "$system" | tee spread-logs/"$system".log; then
 		echo "Spread exited with code $?" >spread-logs/"$system".failed
 	fi
 done

spread.yaml

@@ -5,6 +5,15 @@ backends:
         # TODO: Switch to a released version for better stability.
         type: adhoc
         allocate: |
+            # Spread automatically injects /snap/bin to PATH. When we are
+            # running from the image-garden snap then SPREAD_HOST_PATH is the
+            # original path before such modifications were applied. Snap
+            # applications cannot normally run /snap/bin/* entry-points
+            # successfully so re-set PATH to the original value, as provided by
+            # snapcraft.
+            if [ -n "${SPREAD_HOST_PATH-}" ]; then
+                PATH="${SPREAD_HOST_PATH}"
+            fi
             # Use just enough RAM to link the parser on a virtual system with
             # two cores. Using more cores may easily consume more memory, due
             # to make -j$(nproc), used below than a small CI/CD system is
@@ -38,7 +47,12 @@ backends:
             # Ask image garden to allocate the system and relay the result back
             # to spread as either success of failure.
             exec image-garden allocate "$SPREAD_SYSTEM"."$ARCH"
-        discard: image-garden discard "$SPREAD_SYSTEM_ADDRESS"
+        discard: |
+            # See above for an explanation.
+            if [ -n "${SPREAD_HOST_PATH-}" ]; then
+                PATH="${SPREAD_HOST_PATH}"
+            fi
+            image-garden discard "$SPREAD_SYSTEM_ADDRESS"
         systems:
             # All systems except for the one Ubuntu system are marked as
             # manual. This way we don't accidentally spin up everything when