Merge bitcoin/bitcoin#27033: ci: Cache stuff in volumes, not host folders

fa8e92c022 doc: Update ci docs (721217.xyz)
5fffff54e9 ci: Cache stuff in volumes, not host folders (MarcoFalke)

Pull request description:

  Storing cached stuff in host system folders may lead to unexpected issues when the ci-built stuff is used for a non-ci build or a ci task leaks into another ci task.

ACKs for top commit:
  john-moffett:
    ACK fa8e92c022

Tree-SHA512: 8b0c9019452fbe507a272c1037c3dce3c178c21f85ab1096ed3372ad9d4b3c7aa27d89e5bf80c9a6260ea652e0268be0cbe61d6a4fcb3add569fa38076d32287

ci/README.md

@@ -8,8 +8,7 @@ Be aware that the tests will be built and run in-place, so please run at your ow
 If the repository is not a fresh git clone, you might have to clean files from previous builds or test runs first.
 
 The ci needs to perform various sysadmin tasks such as installing packages or writing to the user's home directory.
-While most of the actions are done inside a docker container, this is not possible for all. Thus, cache directories,
-such as the depends cache, previous release binaries, or ccache, are mounted as read-write into the docker container. While it should be fine to run
+While it should be fine to run
 the ci system locally on you development box, the ci scripts can generally be assumed to have received less review and
 testing compared to other parts of the codebase. If you want to keep the work tree clean, you might want to run the ci
 system in a virtual machine with a Linux operating system of your choice.

ci/test/00_setup_env.sh

@@ -8,11 +8,10 @@ export LC_ALL=C.UTF-8
 
 # The root dir.
 # The ci system copies this folder.
-# This is where the depends build is done.
 BASE_ROOT_DIR=$( cd "$( dirname "${BASH_SOURCE[0]}" )"/../../ >/dev/null 2>&1 && pwd )
 export BASE_ROOT_DIR
 # The depends dir.
-# This folder exists on the ci host and ci guest. Changes are propagated back and forth.
+# This folder exists only on the ci guest, and on the ci host as a volume.
 export DEPENDS_DIR=${DEPENDS_DIR:-$BASE_ROOT_DIR/depends}
 # A folder for the ci system to put temporary files (ccache, datadirs for tests, ...)
 # This folder only exists on the ci host.
@@ -58,12 +57,14 @@ export CCACHE_SIZE=${CCACHE_SIZE:-100M}
 export CCACHE_TEMPDIR=${CCACHE_TEMPDIR:-/tmp/.ccache-temp}
 export CCACHE_COMPRESS=${CCACHE_COMPRESS:-1}
 # The cache dir.
-# This folder exists on the ci host and ci guest. Changes are propagated back and forth.
+# This folder exists only on the ci guest, and on the ci host as a volume.
 export CCACHE_DIR=${CCACHE_DIR:-$BASE_SCRATCH_DIR/.ccache}
 # Folder where the build result is put (bin and lib).
 export BASE_OUTDIR=${BASE_OUTDIR:-$BASE_SCRATCH_DIR/out/$HOST}
 # Folder where the build is done (dist and out-of-tree build).
 export BASE_BUILD_DIR=${BASE_BUILD_DIR:-$BASE_SCRATCH_DIR/build}
+# The folder for previous release binaries.
+# This folder exists only on the ci guest, and on the ci host as a volume.
 export PREVIOUS_RELEASES_DIR=${PREVIOUS_RELEASES_DIR:-$BASE_ROOT_DIR/releases/$HOST}
 export SDK_URL=${SDK_URL:-https://bitcoincore.org/depends-sources/sdks}
 export CI_BASE_PACKAGES=${CI_BASE_PACKAGES:-build-essential libtool autotools-dev automake pkg-config bsdmainutils curl ca-certificates ccache python3 rsync git procps bison}

ci/test/04_install.sh

@@ -39,6 +39,9 @@ if [ -z "$DANGER_RUN_CI_ON_HOST" ]; then
       --build-arg "FILE_ENV=${FILE_ENV}" \
       --tag="${CONTAINER_NAME}" \
       "${BASE_ROOT_DIR}"
+  docker volume create "${CONTAINER_NAME}_ccache" || true
+  docker volume create "${CONTAINER_NAME}_depends" || true
+  docker volume create "${CONTAINER_NAME}_previous_releases" || true
 
   if [ -n "${RESTART_CI_DOCKER_BEFORE_RUN}" ] ; then
     echo "Restart docker before run to stop and clear all containers started with --rm"
@@ -48,9 +51,9 @@ if [ -z "$DANGER_RUN_CI_ON_HOST" ]; then
   # shellcheck disable=SC2086
   CI_CONTAINER_ID=$(docker run $CI_CONTAINER_CAP --rm --interactive --detach --tty \
                   --mount type=bind,src=$BASE_ROOT_DIR,dst=/ro_base,readonly \
-                  --mount type=bind,src=$CCACHE_DIR,dst=$CCACHE_DIR \
-                  --mount type=bind,src=$DEPENDS_DIR,dst=$DEPENDS_DIR \
-                  --mount type=bind,src=$PREVIOUS_RELEASES_DIR,dst=$PREVIOUS_RELEASES_DIR \
+                  --mount "type=volume,src=${CONTAINER_NAME}_ccache,dst=$CCACHE_DIR" \
+                  --mount "type=volume,src=${CONTAINER_NAME}_depends,dst=$DEPENDS_DIR" \
+                  --mount "type=volume,src=${CONTAINER_NAME}_previous_releases,dst=$PREVIOUS_RELEASES_DIR" \
                   -w $BASE_ROOT_DIR \
                   --env-file /tmp/env \
                   --name $CONTAINER_NAME \