From cbe7d0def003b1e159abe9b1caae383d602f79f7 Mon Sep 17 00:00:00 2001
From: Alberto Madonna <alberto.madonna@cscs.ch>
Date: Tue, 20 Feb 2024 18:11:42 +0000
Subject: [PATCH] Added alternate local import procedure using podman's unshare
 and mount commands

Signed-off-by: Alberto Madonna <alberto.madonna@cscs.ch>
---
 enroot.in      | 21 +++++++++++++++++----
 src/docker.sh  | 44 +++++++++++++++++++++++++++++++++++---------
 src/runtime.sh | 11 ++++++++---
 3 files changed, 60 insertions(+), 16 deletions(-)

diff --git a/enroot.in b/enroot.in
index cb3dfa9..2fe8caa 100644
--- a/enroot.in
+++ b/enroot.in
@@ -181,8 +181,11 @@ enroot::usage() {
 		   podman://IMAGE[:TAG]                    Import a Docker image from a local podman repository
 
 		 Options:
-		   -a, --arch    Architecture of the image (defaults to host architecture)
-		   -o, --output  Name of the output image file (defaults to "URI.sqsh")
+		   -a, --arch          Architecture of the image (defaults to host architecture)
+		   -o, --output        Name of the output image file (defaults to "URI.sqsh")
+		   -x, --extract-mode  Determines the way the image is extracted from a local Podman repository.
+		                       This option is ignored when importing images from registries or the Docker daemon.
+		                       Accepted values: tar, mount. Defaults to "tar".
 		EOF
         ;;
     digest)
@@ -349,7 +352,7 @@ enroot::digest() {
 }
 
 enroot::import() {
-    local uri= filename= arch=
+    local uri= filename= arch= extract_mode=tar
 
     while [ $# -gt 0 ]; do
         case "$1" in
@@ -373,6 +376,16 @@ enroot::import() {
            filename="${1#*=}"
            shift
            ;;
+        -x|--extract-mode)
+            [ -z "${2-}" ] && enroot::usage import 1
+            extract_mode="$2"
+            shift 2
+            ;;
+        --extract-mode=*)
+           [ -z "${1#*=}" ] && enroot::usage import 1
+           extract_mode="${1#*=}"
+           shift
+           ;;
         -h|--help)
             enroot::usage import 0 ;;
         --)
@@ -388,7 +401,7 @@ enroot::import() {
     fi
     uri="$1"
 
-    runtime::import "${uri}" "${filename}" "${arch}"
+    runtime::import "${uri}" "${filename}" "${extract_mode}" "${arch}"
 }
 
 enroot::load() {
diff --git a/src/docker.sh b/src/docker.sh
index 41649ec..b0e9c32 100644
--- a/src/docker.sh
+++ b/src/docker.sh
@@ -543,9 +543,31 @@ docker::load() (
                      tar --numeric-owner -C rootfs/ --mode=u-s,g-s -cpf - . | tar --numeric-owner -C '${name}/' -xpf -"
 )
 
+docker::daemon::_config_squash() {
+local -r engine="$1" image="$2" arch="$3" rootfs="$4" filename="$5"
+    "${engine}" inspect "${image}" | common::jq '.[] | with_entries(.key|=ascii_downcase)' > config
+    docker::configure "${rootfs}" config "${arch}"
+
+    # Create the final squashfs filesystem.
+    common::log INFO "Creating squashfs filesystem..." NL
+    mksquashfs "${rootfs}" "${filename}" -all-root ${TTY_OFF+-no-progress} -processors "${ENROOT_MAX_PROCESSORS}" ${ENROOT_SQUASH_OPTIONS} >&2
+}
+
+podman::_mount_squash() {
+    set -euo pipefail
+    shopt -s lastpipe
+    local -r image="$1" arch="$2" container_name="$3" filename="$4"
+    local rootfs=
+
+    rootfs=$(podman mount "${container_name}")
+    docker::daemon::_config_squash podman "${image}" "${arch}" "${rootfs}" "${filename}"
+    podman unmount "${container_name}"
+}
+
 docker::daemon::import() (
     local -r uri="$1"
     local filename="$2" arch="$3"
+    local -r extract_mode="$4"
     local image= tmpdir= engine=
 
     case "${uri}" in
@@ -592,14 +614,18 @@ docker::daemon::import() (
     common::log
 
     # Extract and configure the rootfs.
-    common::log INFO "Extracting image content..."
-    mkdir rootfs
-    "${engine}" export "${PWD##*/}" | tar -C rootfs --warning=no-timestamp --anchored --exclude='dev/*' --exclude='.dockerenv' -px
-    common::fixperms rootfs
-    "${engine}" inspect "${image}" | common::jq '.[] | with_entries(.key|=ascii_downcase)' > config
-    docker::configure rootfs config "${arch}"
+    if [[ "${engine}" == "podman" ]] && [[ "${extract_mode}" == "mount" ]]; then
+        common::log INFO "Mounting image from Podman container..."
+        printf -v cmd "source %q/docker.sh && podman::_mount_squash %q %q %q %q" "${ENROOT_LIBRARY_PATH}" "${image}" "${arch}" "${PWD##*/}" "${filename}"
+        podman unshare bash -c "$cmd"
+    else
+        common::log INFO "Extracting image content..."
+        mkdir rootfs
+        "${engine}" export "${PWD##*/}" | tar -C rootfs --warning=no-timestamp --anchored --exclude='dev/*' --exclude='.dockerenv' -px
+        common::fixperms rootfs
+        docker::daemon::_config_squash "${engine}" "${image}" "${arch}" rootfs "${filename}"
+    fi
 
-    # Create the final squashfs filesystem.
-    common::log INFO "Creating squashfs filesystem..." NL
-    mksquashfs rootfs "${filename}" -all-root ${TTY_OFF+-no-progress} -processors "${ENROOT_MAX_PROCESSORS}" ${ENROOT_SQUASH_OPTIONS} >&2
+    # Cleanup the container created to extract the rootfs
+    "${engine}" rm "${PWD##*/}"
 )
diff --git a/src/runtime.sh b/src/runtime.sh
index 0b65078..14a5c63 100644
--- a/src/runtime.sh
+++ b/src/runtime.sh
@@ -441,8 +441,13 @@ runtime::digest() {
 }
 
 runtime::import() {
-    local -r uri="$1" filename="$2"
-    local arch="$3"
+    local -r uri="$1" filename="$2" extract_mode="$3"
+    local arch="${4-}"
+
+    # Check the extract mode value.
+    if [[ "${extract_mode}" != "tar" ]] && [[ "${extract_mode}" != "mount" ]]; then
+        common::err "Invalid extract mode: ${extract_mode}"
+    fi
 
     # Use the host architecture as the default.
     if [ -z "${arch}" ]; then
@@ -454,7 +459,7 @@ runtime::import() {
     docker://*)
         docker::import "${uri}" "${filename}" "${arch}" ;;
     dockerd://* | podman://*)
-        docker::daemon::import "${uri}" "${filename}" "${arch}" ;;
+        docker::daemon::import "${uri}" "${filename}" "${arch}" "${extract_mode}" ;;
     *)
         common::err "Invalid argument: ${uri}" ;;
     esac