Merge feature/xenial_snap_bases into ubuntu/xenial [a=rcj] [r=jchittum]

Backport snap pre-seed base support (LP: #1874834)

Xenial builds with core18-based snaps pre-seed core snap instead core18
and snapd.  This patch is a backport of snap pre-seeding functionality
that is snap base aware.

MP: https://code.launchpad.net/~rcj/livecd-rootfs/+git/livecd-rootfs/+merge/382939

debian/changelog

@@ -1,3 +1,9 @@
+livecd-rootfs (2.408.59) xenial; urgency=medium
+
+  * Backport snap preseed base support (LP: #1874834)
+
+ -- Robert C Jennings <robert.jennings@canonical.com>  Fri, 24 Apr 2020 10:54:54 -0500
+
 livecd-rootfs (2.408.58) xenial; urgency=medium
 
   * Use a snap cohort key for consistent parallel builds (LP: #1866159)

live-build/functions

@@ -349,6 +349,47 @@ release_ver() {
     distro-info --series="$LB_DISTRIBUTION" -r | awk '{ print $1 }'
 }
 
+_snap_post_process() {
+    # Look for the 'core' snap. If it is not present, assume that the image
+    # contains only snaps with bases >= core18. In that case snapd is
+    # preseeded. However, when 'core' is being installed and snapd has not
+    # been installed by a call to 'snap_preseed' (see below) then it is
+    # removed again.
+    local CHROOT_ROOT=$1
+    local SNAP_NAME=$2
+
+    local seed_dir="$CHROOT_ROOT/var/lib/snapd/seed"
+    local snaps_dir="$seed_dir/snaps"
+    local seed_yaml="$seed_dir/seed.yaml"
+    local assertions_dir="$seed_dir/assertions"
+    local snapd_install_stamp="$seed_dir/.snapd-explicit-install-stamp"
+
+    case $SNAP_NAME in
+        core[0-9]*)
+            # If the 'core' snap is not present, assume we are coreXX-only and
+            # install the snapd snap.
+            if [ ! -f ${snaps_dir}/core_[0-9]*.snap ]; then
+                _snap_preseed $CHROOT_ROOT snapd stable
+            fi
+            ;;
+        core)
+            # If the snapd snap has been seeded, but not marked as explicitly
+            # installed (see snap_preseed below), then remove it.
+            if [ -f ${snaps_dir}/snapd_[0-9]*.snap ] && \
+                    [ ! -f "$snapd_install_stamp" ]
+            then
+                # Remove snap, assertions and entry in seed.yaml
+                rm -f ${snaps_dir}/snapd_[0-9]*.snap
+                rm -f ${assertions_dir}/snapd_[0-9]*.assert
+                sed -i -e'N;/name: snapd/,+2d' $seed_yaml
+            fi
+            ;;
+        *)
+            # ignore
+            ;;
+    esac
+}
+
 _snap_preseed() {
     # Download the snap/assertion and add to the preseed
     local CHROOT_ROOT=$1
@@ -363,12 +404,18 @@ _snap_preseed() {
 
     # Download the snap & assertion
     local snap_download_failed=0
-    chroot $CHROOT_ROOT sh -c "
+
+    # Preseed a snap only once
+    if [ -f ${snaps_dir}/${SNAP_NAME}_[0-9]*.snap ]; then
+        return
+    fi
+
+    sh -c "
         set -x;
-        cd /var/lib/snapd/seed;
+        cd \"$CHROOT_ROOT/var/lib/snapd/seed\";
         SNAPPY_STORE_NO_CDN=1 snap download \
             --cohort="${COHORT_KEY:-}" \
-            --channel=$CHANNEL \"$SNAP_NAME\"" || snap_download_failed=1
+            --channel=\"$CHANNEL\" \"$SNAP_NAME\"" || snap_download_failed=1
     if [ $snap_download_failed = 1 ] ; then
         echo "If the channel ($CHANNEL) includes '*/ubuntu-##.##' track per "
         echo "Ubuntu policy (ex. stable/ubuntu-18.04) the publisher will need "
@@ -381,6 +428,35 @@ _snap_preseed() {
     mv -v $seed_dir/*.assert $assertions_dir
     mv -v $seed_dir/*.snap $snaps_dir
 
+    # Pre-seed snap's base
+    case $SNAP_NAME in
+        snapd)
+            # snapd is self-contained, ignore base
+            ;;
+        core|core[0-9][0-9])
+            # core and core## are self-contained, ignore base
+            ;;
+        *)
+            # Determine which core snap is needed
+            local snap_info
+
+            # snap info doesn't have --channel, so must run agains the downloaded snap
+            snap_info=$(snap info --verbose ${snaps_dir}/${SNAP_NAME}_[0-9]*.snap)
+
+            if [ $? -ne 0 ]; then
+                echo "Failed to retrieve base of $SNAP_NAME!"
+                exit 1
+            fi
+
+            local core_snap=$(echo "$snap_info" | grep '^base:' | awk '{print $2}')
+
+            # If snap info does not list a base use 'core'
+            core_snap=${core_snap:-core}
+
+            _snap_preseed $CHROOT_ROOT $core_snap stable
+            ;;
+    esac
+
     # Add the snap to the seed.yaml
     ! [ -e $seed_yaml ] && echo "snaps:" > $seed_yaml
     cat <<EOF >> $seed_yaml
@@ -393,6 +469,8 @@ EOF
 
     echo -n "    file: " >> $seed_yaml
     (cd $snaps_dir; ls -1 ${SNAP_NAME}_*.snap) >> $seed_yaml
+
+    _snap_post_process $CHROOT_ROOT $SNAP_NAME
 }
 
 snap_prepare_assertions() {
@@ -444,25 +522,43 @@ snap_prepare() {
     # used for the image's model assertion
     local CUSTOM_BRAND_MODEL=${2:-generic:generic-classic}
 
-    local seed_dir="$CHROOT_ROOT/var/lib/snapd/seed"
-    local snaps_dir="$seed_dir/snaps"
-
     snap_prepare_assertions "$CHROOT_ROOT" "$CUSTOM_BRAND_MODEL"
-
-    # Download the core snap
-    if ! [ -f $snaps_dir/core_[0-9]*.snap ] ; then
-        _snap_preseed $CHROOT_ROOT core stable
-    fi
 }
 
 snap_preseed() {
     # Preseed a snap in the image
     local CHROOT_ROOT=$1
     local SNAP=$2
+    local SNAP_NAME=${SNAP%/*}
     # Per Ubuntu policy, all seeded snaps (with the exception of the core
     # snap) must pull from stable/ubuntu-$(release_ver) as their channel.
     local CHANNEL=${3:-"stable/ubuntu-$(release_ver)"}
 
     snap_prepare $CHROOT_ROOT
     _snap_preseed $CHROOT_ROOT $SNAP $CHANNEL
+
+    # Mark this image as having snapd installed explicitly.
+    case $SNAP_NAME in
+        snapd)
+            touch "$CHROOT_ROOT/var/lib/snapd/seed/.snapd-explicit-install-stamp"
+            ;;
+    esac
+
+    # Do basic validation of generated snapd seed.yaml, doing it here
+    # means we catch all the places(tm) that snaps are added but the
+    # downside is that each time a snap is added the seed must be valid,
+    # i.e. snaps with bases need to add bases first etc
+    #
+    # Skip validation by setting SNAP_NO_VALIDATE_SEED=1.
+    if [ -z "${SNAP_NO_VALIDATE_SEED:-}" ]; then
+        snap_validate_seed "${CHROOT_ROOT}"
+    fi
+}
+
+snap_validate_seed() {
+    local CHROOT_ROOT=$1
+
+    if [ -e "${CHROOT_ROOT}/var/lib/snapd/seed/seed.yaml" ]; then
+        snap debug validate-seed "${CHROOT_ROOT}/var/lib/snapd/seed/seed.yaml"
+    fi
 }