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lb_chroot_layered: use rsync to make more minimal overlay layers. (LP: #2028213)

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This commit is contained in:
Michael Hudson-Doyle 2023-07-26 20:53:05 +12:00
parent 276d577722
commit cf75120068
2 changed files with 19 additions and 57 deletions
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4
debian/changelog vendored
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@ -5,6 +5,10 @@ livecd-rootfs (23.10.8) UNRELEASED; urgency=medium
for the StarFive VisionFive 2 board. As it is larger than U-Boot we need
to increase the size of the loader 2 partition to accommodate it.
[ Michael Hudson-Doyle ]
* lb_chroot_layered: use rsync to make more minimal overlay layers.
(LP: #2028213)
-- Michael Hudson-Doyle <michael.hudson@ubuntu.com> Wed, 02 Aug 2023 13:12:09 +1200
livecd-rootfs (23.10.7) mantic; urgency=medium

72
live-build/lb_chroot_layered
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@ -107,57 +107,6 @@ lb_chroot_includes () {
cd "${OLDPWD}"
}
reduce_pass_size () {
# Remove duplicated files between parent and current pass
# Note the empty directories created in a child pass are not removed
local pass=$1
local parent="$(get_parent_pass $pass)"
$(is_root_layer $pass) && return
pass_dir="overlay.${pass}"
parent_pass_dir="overlay.${parent}"
local list_pass=$(mktemp)
local list_parent=$(mktemp)
(cd $pass_dir && find . ! -type d -printf "%h/%f|%s|%y|%U|%G|%m\n"|sort > $list_pass)
(cd $parent_pass_dir && find . ! -type d -printf "%h/%f|%s|%y|%U|%G|%m\n"|sort > $list_parent)
# Only iterate on common files with same type, owner, permission and size
comm -12 $list_pass $list_parent|cut -d'|' -f1|while read f; do
# If file contents are different, keep it
if ! diff --brief --no-dereference "$pass_dir/$f" "$parent_pass_dir/$f" >/dev/null; then
continue
fi
p="$(dirname "$f")"
while [ "$p" != . ]; do
# As explained in the overlayfs documentation
# https://www.kernel.org/doc/html/latest/filesystems/overlayfs.html#whiteouts-and-opaque-directories
# an xattr of trusted.overlay.opaque indicates an 'opaque' directory
# that was deleted from the overlay. Removing files from within the
# directory, even if identical with one in the lower layer, will result
# in it going missing from the combined filesystem.
#
# It would be possible to be more clever, e.g. if the two directories
# are still similar, we could the delete the attribute and convert any
# still-needed deletions to whiteouts but it doesn't seem worth it in
# the cases seen so far.
if [ -n "$(getfattr -n trusted.overlay.opaque -h --only-values -- "$pass_dir/$p" 2>/dev/null)" ]; then
Echo_message "reduce_pass_size: '%s' would be removed from overlay but for trusted.overlay.opaque on '%s'" "$f" "$p"
continue 2
fi
p="$(dirname "$p")"
done
# Files are strictly identical between the 2 passes (only mod or access times differs). No need for unused delta.
Echo_message "reduce_pass_size: '%s' is strictly identical between %s and %s. Removing." "$f" "$pass" "$parent"
rm "$pass_dir/$f"
done
rm $list_pass
rm $list_parent
}
create_chroot_pass () {
local pass=$1
shift 1 # restore ${*}
@ -182,8 +131,8 @@ create_chroot_pass () {
mkdir -p "$overlay_dir/"
lowerdirs=$(get_lowerdirs_for_pass $pass)
if [ -n "$lowerdirs" ]; then
mkdir -p chroot/
mount_overlay "$lowerdirs" "$overlay_dir" chroot/
mkdir -p chroot "${overlay_dir}-initial"
mount_overlay "$lowerdirs" "${overlay_dir}-initial" chroot/
else
ln -s "$overlay_dir/" chroot
fi
@ -319,13 +268,22 @@ create_chroot_pass () {
lb chroot_devpts remove ${*}
if [ -n "$lowerdirs" ]; then
umount chroot
rmdir chroot
# Although the current chroot was created as an overlay over
# the previous layer, many operations can result in redundant
# files in the upperdir. Rather than trying to minimize the
# overlay by hand, we rsync the chroot into a fresh overlay,
# rely on rsyncs ability to avoid redundant file operations,
# and take _that_ overlay's upperdir as the content of the
# layer.
mkdir chroot-2
mount_overlay "$lowerdirs" "$overlay_dir" chroot-2/
rsync -aXHAS --del chroot/ chroot-2/
umount chroot chroot-2
rmdir chroot chroot-2
rm -rf ${overlay_dir}-initial
else
rm chroot
fi
reduce_pass_size $pass
}
if [ ! -d chroot.bootstrap/ ]; then