Makefile,makerootfs.sh: implement LIVE_FAST=1 option for make live

The LIVE_FAST=1 uses the recent '--input-tar' parameter for the linuxkit
tool, which helps to generate the tarball faster by copying content which
was not changed since the previous invocation.

Time measurements for the separate makerootfs.sh call:

  ./tools/makerootfs.sh tar -u -y rootfs-kvm-generic.yml -t rootfs.tar -d installer -a amd64

before
------
real    0m48.262s
user    0m50.457s
sys     0m2.226s

with the LIVE_FAST=1
--------------------
real    0m8.240s
user    0m7.287s
sys     0m2.529s

For now this feature considered as experimental, so no documentation
or usage is included in makefile. Hopefully we can make this mode as
default.

Signed-off-by: Roman Penyaev <[email protected]>

Makefile

@@ -295,11 +295,19 @@ DOCKER_GO = _() { $(SET_X); mkdir -p $(CURDIR)/.go/src/$${3:-dummy} ; mkdir -p $
 
 PARSE_PKGS=$(if $(strip $(EVE_HASH)),EVE_HASH=)$(EVE_HASH) DOCKER_ARCH_TAG=$(DOCKER_ARCH_TAG) KERNEL_TAG=$(KERNEL_TAG) ./tools/parse-pkgs.sh
 LINUXKIT=$(BUILDTOOLS_BIN)/linuxkit
-LINUXKIT_VERSION=3a0405298aab1632524a6ccd074969b417e1ee92
+LINUXKIT_VERSION=e6b0ae05eb3a2b99e84d9ffc03a3a5c9c3e7e371
 LINUXKIT_SOURCE=https://github.com/linuxkit/linuxkit.git
 LINUXKIT_OPTS=$(if $(strip $(EVE_HASH)),--hash) $(EVE_HASH) $(if $(strip $(EVE_REL)),--release) $(EVE_REL)
 LINUXKIT_PKG_TARGET=build
 LINUXKIT_PATCHES_DIR=tools/linuxkit/patches
+
+ifdef LIVE_FAST
+# Check the makerootfs.sh and the linuxkit tool invocation, the --input-tar
+# parameter specifically. This will create a new tar based on the old one
+# (already generated), which speeds tar generation up a bit.
+UPDATE_TAR=-u
+endif
+
 RESCAN_DEPS=FORCE
 # set FORCE_BUILD to --force to enforce rebuild
 FORCE_BUILD=
@@ -643,7 +651,7 @@ $(ROOTFS)-%.img: $(ROOTFS_IMG)
 
 $(ROOTFS_TAR): images/out/rootfs-$(HV)-$(PLATFORM).yml | $(INSTALLER)
 	$(QUIET): $@: Begin
-	./tools/makerootfs.sh tar -y $< -t $@ -d $(INSTALLER) -a $(ZARCH)
+	./tools/makerootfs.sh tar $(UPDATE_TAR) -y $< -t $@ -d $(INSTALLER) -a $(ZARCH)
 	$(QUIET): $@: Succeeded
 ifdef KERNEL_IMAGE
 	# Consider this as a cry from the heart: enormous amount of time is

tools/makerootfs.sh

@@ -41,9 +41,23 @@ do_tar() {
   if [ -n "$arch" ]; then
     ARCHARG="--arch ${arch}"
   fi
-  # sbom disabled for now; will be re-enabled later
-  # shellcheck disable=SC2086
-  linuxkit build --no-sbom --docker ${ARCHARG} --o "${tarfile}" "$ymlfile"
+  if [ -z "$updatetar" ] || [ ! -e "${tarfile}" ]; then
+    # sbom disabled for now; will be re-enabled later
+    # shellcheck disable=SC2086
+    linuxkit build --no-sbom --docker ${ARCHARG} --o "${tarfile}" "$ymlfile"
+  else
+    # sbom disabled for now; will be re-enabled later
+    # shellcheck disable=SC2086
+    linuxkit build --no-sbom --docker ${ARCHARG} --o "${tarfile}.new" --input-tar "${tarfile}"  "$ymlfile"
+    newmd5=$(md5sum "${tarfile}.new" | awk '{print $1}')
+    oldmd5=$(md5sum "${tarfile}" | awk '{print $1}')
+    # Don't touch the modification time if files are equal. Crucial for Makefile.
+    if [ "$newmd5" != "$oldmd5" ]; then
+      mv "${tarfile}.new" "${tarfile}"
+    else
+      rm "${tarfile}.new"
+    fi
+  fi
 }
 
 # mode 2 - generate image from tarfile
@@ -113,8 +127,8 @@ help() {
 mode="$1"
 shift
 
-unset tarfile imgfile arch format ymlfile execidr
-while getopts "t:i:a:f:y:d:h" o
+unset tarfile imgfile arch format ymlfile execidr updatetar
+while getopts "t:i:a:f:y:d:uh" o
 do
   case $o in
     t)
@@ -135,6 +149,9 @@ do
     d)
       execdir=$(abspath "$OPTARG")
       ;;
+    u)
+      updatetar=1
+      ;;
     h)
       help
       ;;