Standardize on OCI images in test-suite

Instead of manually bootstrapping our own base "image" using a host
specific script, just use the official, prebuilt OCI images with
Podman/Docker.  This has several advantages:

- Standard, ubiquitous OCI images (easy support for other distros)
- No manual setup of DNF, RPM macros, user namespaces and whatnot
- Single recipe (Dockerfile) for both the local and CI purposes
- Outsourced image caching (Podman storage)
- Faster (just downloads the prebuilt image)
- Less dependencies on the host

Now that we've prepared mktree.podman for local use, just switch to it
in cmake and remove the Fedora backend.  Update the docs and comments
accordingly, too, those should explain the details.

Fixes: #2643

.gitignore

@@ -7,4 +7,3 @@
 
 /_build
 /docs/_site
-/mktree.*

tests/CMakeLists.txt

@@ -71,40 +71,32 @@ if (nproc GREATER 1)
 	set(JOBS -j${nproc})
 endif()
 
-# Detect suitable mktree backend
-find_program(BWRAP bwrap)
-mark_as_advanced(BWRAP)
-find_program(PODMAN NAMES podman docker)
-mark_as_advanced(PODMAN)
-if ("${MKTREE_BACKEND}" STREQUAL "")
-	if (BWRAP AND EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/mktree.${OS_NAME})
-		set(MKTREE_BACKEND ${OS_NAME})
-	elseif (PODMAN)
-		set(MKTREE_BACKEND podman)
-	else()
-		message(WARNING
-			"No suitable mktree backend found for this platform. "
-			"Disabling test-suite.")
-		return()
-	endif()
-endif()
-message(STATUS "Using mktree backend: ${MKTREE_BACKEND}")
-
 # Set up mktree
-if ("${MKTREE_BACKEND}" STREQUAL "podman")
+set(MKTREE_BACKEND podman CACHE STRING "Mktree backend to use")
+if (MKTREE_BACKEND STREQUAL "podman")
 	find_program(PODMAN NAMES podman docker REQUIRED)
-	configure_file(Dockerfile Dockerfile COPYONLY)
-else()
-	find_program(BWRAP bwrap REQUIRED)
-	if (PODMAN)
-		get_filename_component(PODMAN ${PODMAN} NAME)
+	find_program(BUILDAH buildah)
+	get_filename_component(PODMAN_NAME ${PODMAN} NAME)
+	mark_as_advanced(PODMAN PODMAN_NAME BUILDAH)
+	if (PODMAN_NAME STREQUAL "podman" AND BUILDAH AND
+	    EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/Dockerfile.${OS_NAME})
+		set(MKTREE_NATIVE ON)
+		configure_file(Dockerfile.${OS_NAME} Dockerfile COPYONLY)
 		add_custom_target(ci
-			COMMAND ./mktree.${PODMAN} build
-			COMMAND ./mktree.${PODMAN} check ${JOBS} $(TESTOPTS)
+			COMMAND ./mktree.podman build
+			COMMAND ./mktree.podman check --log ${JOBS} $(TESTOPTS)
 			WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
 		)
+	else()
+		set(MKTREE_NATIVE OFF)
+		configure_file(Dockerfile Dockerfile COPYONLY)
 	endif()
+	set(MKTREE_MODE " (native: ${MKTREE_NATIVE})")
+elseif(MKTREE_BACKEND STREQUAL "rootfs")
+	find_program(BWRAP bwrap REQUIRED)
+	mark_as_advanced(BWRAP)
 endif()
+message(STATUS "Using mktree backend: ${MKTREE_BACKEND}${MKTREE_MODE}")
 configure_file(mktree.common mktree.common @ONLY)
 configure_file(mktree.${MKTREE_BACKEND} mktree @ONLY)
 

tests/README.md

@@ -1,8 +1,25 @@
-To run these tests, you need at least these dependencies on the host:
+To run these tests, you need either of:
 
-1.    [bwrap](https://github.com/containers/bubblewrap/)
-1.    [gdb](https://www.gnu.org/software/gdb/)
-1.    [gnupg](https://www.gnupg.org/) >= 2.0
+1.    [podman](https://github.com/containers/podman)
+1.    [docker](https://github.com/docker)
+
+Optionally, the following is also recommended (see below):
+
+1.    [buildah](https://github.com/containers/buildah)
+
+The test suite runs in a Podman/Docker container and supports two modes:
+
+1. *Native* - Exercises the local build of RPM against a minimal image of the
+   host Linux distribution.  Currently, only Fedora Linux is supported.  This
+   mode is optimized for local RPM development and requires Podman and Buildah.
+1. *Non-native* - Performs a fresh build of RPM (including cmake configuration)
+   from the local checkout as part of a Fedora-based image.  This mode is
+   optimized for portability (CI environment) and works with both Podman and
+   Docker.
+
+The mode is selected automatically by cmake based on the host distribution and
+the container tools installed, with the native mode being preferred whenever
+possible.
 
 Then run the command
 
@@ -32,16 +49,21 @@ For all available options, see the output of the command:
 By default, tests are executed in parallel using all available cores, pass
 a specific -jN value to limit.
 
-To drop into an Autotest-like shell, run:
+To drop into an interactive Autotest-like shell, run:
 
     make atshell
 
-See the printed help for details on how to use it.
+This is like a singular, empty `RPMTEST_CHECK()` with a shell running in it and
+a writable tree available at the path stored in `$RPMTEST`.  From this shell,
+you can run the same commands as a normal test would, such as `runroot rpm`.
+This can be used to quickly prototype (or debug) a test.
 
-You can also run a containerized shell with your RPM checkout:
+You can also drop straight into the `$RPMTEST` container like so:
 
     make shell
 
-To factory-reset the container, run:
+This is just a shorthand for `make atshell` followed by `runroot_other bash`.
+
+To factory-reset the `$RPMTEST` container, run:
 
     make reset

tests/mktree.podman

@@ -1,7 +1,15 @@
 #!/bin/bash
 #
-# Podman-based mktree backend using an OCI image to build and run RPM.
-# Works standalone (outside of a build directory) too.
+# Podman-based mktree backend using OCI images.
+#
+# If a Dockerfile matching the host distribution is found, it is built and then
+# combined with the local RPM build to produce the final image ("native" mode).
+# Otherwise, the default Dockerfile is used and RPM is built as part of the
+# image ("non-native" mode).
+#
+# This script can also be invoked directly from the source directory, in which
+# case it performs a non-native build (useful for CI purposes).  If invoked via
+# the mktree.docker symlink, docker is used instead of podman.
 
 PROGRAM=$(basename $0)
 if [ "$PROGRAM" == "mktree" ]; then