From 5a42bd8565207627314dcee813e78aca8926ff3e Mon Sep 17 00:00:00 2001
From: Michael Marineau <michael.marineau@coreos.com>
Date: Wed, 3 Feb 2016 17:16:28 -0800
Subject: [PATCH 1/8] setup_board: cleanup flags section

Move most flags into the usage message and use a more consistent style.
---
 setup_board | 34 +++++++++++++++++-----------------
 1 file changed, 17 insertions(+), 17 deletions(-)

diff --git a/setup_board b/setup_board
index 725901954f..aa2a1e5d42 100755
--- a/setup_board
+++ b/setup_board
@@ -13,14 +13,26 @@ restart_in_chroot_if_needed "$@"
 assert_not_root_user
 
 # Developer-visible flags.
-DEFINE_string board "$DEFAULT_BOARD" \
+DEFINE_string board "${DEFAULT_BOARD}" \
   "The name of the board to set up."
-DEFINE_boolean default $FLAGS_FALSE \
+DEFINE_boolean default "${FLAGS_FALSE}" \
   "Set board to the default board in your chroot"
-DEFINE_boolean force $FLAGS_FALSE \
+DEFINE_boolean force "${FLAGS_FALSE}" \
   "Force re-creating board root."
-DEFINE_boolean usepkg $FLAGS_TRUE \
-  "Use binary packages to bootstrap."
+DEFINE_boolean usepkg "${FLAGS_TRUE}" \
+  "Use binary packages when possible."
+DEFINE_boolean getbinpkg "${FLAGS_TRUE}" \
+  "Download binary packages from remote repository."
+DEFINE_string getbinpkgver "" \
+  "Use binary packages from a specific version."
+DEFINE_boolean toolchainpkgonly "${FLAGS_FALSE}" \
+  "Use binary packages only for the board toolchain."
+DEFINE_integer jobs "${NUM_JOBS}" \
+  "How many packages to build in parallel at maximum."
+DEFINE_boolean skip_toolchain_update "${FLAGS_FALSE}" \
+  "Don't update toolchain automatically."
+DEFINE_boolean skip_chroot_upgrade "${FLAGS_FALSE}" \
+  "Don't run the chroot upgrade automatically; use with care."
 
 FLAGS_HELP="usage: $(basename $0) [flags]
 
@@ -33,26 +45,14 @@ show_help_if_requested "$@"
 # The following options are advanced options, only available to those willing
 # to read the source code. They are not shown in help output, since they are
 # not needed for the typical developer workflow.
-DEFINE_string getbinpkgver "" \
-  "Use binary packages from a specific version."
-DEFINE_boolean toolchainpkgonly $FLAGS_FALSE \
-  "Use binary packages only for the board toolchain."
-DEFINE_integer jobs "${NUM_JOBS}" \
-  "How many packages to build in parallel at maximum."
 DEFINE_string libc_version "[stable]" \
   "Version of libc to use."
 DEFINE_boolean quiet $FLAGS_FALSE \
   "Don't print warnings when board already exists."
-DEFINE_boolean skip_toolchain_update $FLAGS_FALSE \
-  "Don't update toolchain automatically."
-DEFINE_boolean skip_chroot_upgrade $FLAGS_FALSE \
-  "Don't run the chroot upgrade automatically; use with care."
 DEFINE_string variant "" \
   "Board variant."
 DEFINE_boolean regen_configs ${FLAGS_FALSE} \
   "Regenerate all config files (useful for modifying profiles w/out rebuild)."
-DEFINE_boolean getbinpkg $FLAGS_TRUE \
-  "Passed to update_chroot, ignored by setup_board itself."
 
 
 # builds wrappers like equery-arm-generic.

From 602412fd2af4e31cce8a0c1fb30a5ebcbb656d14 Mon Sep 17 00:00:00 2001
From: Michael Marineau <michael.marineau@coreos.com>
Date: Wed, 3 Feb 2016 17:23:20 -0800
Subject: [PATCH 2/8] build_packages: remove unused --accept_licenses

This flag was dropped from setup_board way back in commit 7d6619df8.
---
 build_packages | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/build_packages b/build_packages
index 23722d68dd..8369b5ba82 100755
--- a/build_packages
+++ b/build_packages
@@ -45,8 +45,6 @@ DEFINE_string getbinpkgver "" \
   "Use binary packages from a specific version."
 DEFINE_boolean toolchainpkgonly $FLAGS_FALSE \
   "Use binary packages only for the board toolchain."
-DEFINE_string accept_licenses "" \
-  "Licenses to append to the accept list."
 DEFINE_integer jobs "${NUM_JOBS}" \
   "How many packages to build in parallel at maximum."
 DEFINE_boolean rebuild "${FLAGS_FALSE}" \
@@ -82,9 +80,6 @@ CHROMITE_BIN="${GCLIENT_ROOT}/chromite/bin"
 
 # Before we can run any tools, we need to update chroot or setup_board.
 UPDATE_ARGS=( --regen_configs )
-if [[ -n ${FLAGS_accept_licenses} ]]; then
-  UPDATE_ARGS+=( --accept_licenses "${FLAGS_accept_licenses}" )
-fi
 if [ "${FLAGS_usepkg}" -eq "${FLAGS_TRUE}" ]; then
   UPDATE_ARGS+=( --usepkg )
   if [[ "${FLAGS_getbinpkg}" -eq "${FLAGS_TRUE}" ]]; then

From 10a7864ff09e30bf4bafeb4a705fd5a5c038f965 Mon Sep 17 00:00:00 2001
From: Michael Marineau <michael.marineau@coreos.com>
Date: Wed, 3 Feb 2016 17:26:20 -0800
Subject: [PATCH 3/8] build_packages: flip weird inverted boolean flag

Use `--workon` and `--noworkon` instead of `--nonoworkon` and `--noworkon`
---
 build_packages | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/build_packages b/build_packages
index 8369b5ba82..ccc5565622 100755
--- a/build_packages
+++ b/build_packages
@@ -18,8 +18,8 @@ DEFINE_boolean usepkg "${FLAGS_TRUE}" \
   "Use binary packages to bootstrap when possible."
 DEFINE_boolean getbinpkg "${FLAGS_TRUE}" \
   "Download binary packages from remote repository."
-DEFINE_boolean noworkon "${FLAGS_FALSE}" \
-  "Don't force-build workon packages."
+DEFINE_boolean workon "${FLAGS_TRUE}" \
+  "Automatically rebuild updated cros-workon packages."
 DEFINE_boolean fetchonly "${FLAGS_FALSE}" \
   "Don't build anything, instead only fetch what is needed."
 
@@ -154,7 +154,7 @@ fi
 
 # Build cros_workon packages when they are changed.
 CROS_WORKON_PKGS=()
-if [ "${FLAGS_noworkon}" -eq "${FLAGS_FALSE}" ]; then
+if [ "${FLAGS_workon}" -eq "${FLAGS_TRUE}" ]; then
   LIST_MODIFIED_PACKAGES="${CHROMITE_BIN}/cros_list_modified_packages"
   CROS_WORKON_PKGS+=( $("${LIST_MODIFIED_PACKAGES}" --board=${FLAGS_board}) )
 fi

From bf104d415e79f4e303957745c0b82650d5f1c8d8 Mon Sep 17 00:00:00 2001
From: Michael Marineau <michael.marineau@coreos.com>
Date: Wed, 3 Feb 2016 17:30:10 -0800
Subject: [PATCH 4/8] build_packages: remove old --reuse_pkgs_from_local_boards
 flag

Removed from setup_board in ancient times e6b3c608.
---
 build_packages | 14 +-------------
 1 file changed, 1 insertion(+), 13 deletions(-)

diff --git a/build_packages b/build_packages
index ccc5565622..8e05c9b485 100755
--- a/build_packages
+++ b/build_packages
@@ -54,14 +54,6 @@ DEFINE_boolean skip_chroot_upgrade "${FLAGS_FALSE}" \
 DEFINE_boolean skip_toolchain_update "${FLAGS_FALSE}" \
   "Don't update toolchain automatically."
 
-# The --reuse_pkgs_from_local_boards flag tells Portage to share binary
-# packages between boards that are built locally, so that the total time
-# required to build several boards is reduced. This flag is only useful
-# when you are not able to use remote binary packages, since remote binary
-# packages are usually more up to date than anything you have locally.
-DEFINE_boolean reuse_pkgs_from_local_boards $FLAGS_FALSE \
-  "Bootstrap from local packages instead of remote packages."
-
 # Parse command line
 FLAGS "$@" || exit 1
 eval set -- "${FLAGS_ARGV}"
@@ -101,9 +93,6 @@ fi
 if [[ "${FLAGS_jobs}" -ne -1 ]]; then
   UPDATE_ARGS+=( --jobs=${FLAGS_jobs} )
 fi
-if [ "${FLAGS_reuse_pkgs_from_local_boards}" -eq "${FLAGS_TRUE}" ]; then
-  UPDATE_ARGS+=( --reuse_pkgs_from_local_boards )
-fi
 if [ "${FLAGS_skip_toolchain_update}" -eq "${FLAGS_TRUE}" ]; then
   UPDATE_ARGS+=( --skip_toolchain_update )
 fi
@@ -128,8 +117,7 @@ fi
 
 EMERGE_CMD+=( ${EXTRA_BOARD_FLAGS} )
 
-if [[ "${FLAGS_usepkg}" -eq "${FLAGS_TRUE}" ||
-      "${FLAGS_reuse_pkgs_from_local_boards}" -eq "${FLAGS_TRUE}" ]]; then
+if [[ "${FLAGS_usepkg}" -eq "${FLAGS_TRUE}" ]]; then
   # Use binary packages. Include all build-time dependencies,
   # so as to avoid unnecessary differences between source
   # and binary builds.

From a42ffcddbbf928d76e751b2f746fed7acf497486 Mon Sep 17 00:00:00 2001
From: Michael Marineau <michael.marineau@coreos.com>
Date: Wed, 3 Feb 2016 17:34:32 -0800
Subject: [PATCH 5/8] build_packages: include all flags in usage message

---
 build_packages | 31 +++++++++++++------------------
 1 file changed, 13 insertions(+), 18 deletions(-)

diff --git a/build_packages b/build_packages
index 8e05c9b485..a2820fdf40 100755
--- a/build_packages
+++ b/build_packages
@@ -15,13 +15,25 @@ assert_not_root_user
 DEFINE_string board "${DEFAULT_BOARD}" \
   "The board to build packages for."
 DEFINE_boolean usepkg "${FLAGS_TRUE}" \
-  "Use binary packages to bootstrap when possible."
+  "Use binary packages when possible."
 DEFINE_boolean getbinpkg "${FLAGS_TRUE}" \
   "Download binary packages from remote repository."
+DEFINE_string getbinpkgver "" \
+  "Use binary packages from a specific version."
+DEFINE_boolean toolchainpkgonly "${FLAGS_FALSE}" \
+  "Use binary packages only for the board toolchain."
 DEFINE_boolean workon "${FLAGS_TRUE}" \
   "Automatically rebuild updated cros-workon packages."
 DEFINE_boolean fetchonly "${FLAGS_FALSE}" \
   "Don't build anything, instead only fetch what is needed."
+DEFINE_integer jobs "${NUM_JOBS}" \
+  "How many packages to build in parallel at maximum."
+DEFINE_boolean rebuild "${FLAGS_FALSE}" \
+  "Automatically rebuild dependencies."
+DEFINE_boolean skip_toolchain_update "${FLAGS_FALSE}" \
+  "Don't update toolchain automatically."
+DEFINE_boolean skip_chroot_upgrade "${FLAGS_FALSE}" \
+  "Don't run the chroot upgrade automatically; use with care."
 
 # include upload options
 . "${BUILD_LIBRARY_DIR}/release_util.sh" || exit 1
@@ -36,23 +48,6 @@ up by the build_image script to put together a bootable CoreOS image.
 If [packages] are specified, only build those specific packages (and any
 dependencies they might need).
 "
-show_help_if_requested "$@"
-
-# The following options are advanced options, only available to those willing
-# to read the source code. They are not shown in help output, since they are
-# not needed for the typical developer workflow.
-DEFINE_string getbinpkgver "" \
-  "Use binary packages from a specific version."
-DEFINE_boolean toolchainpkgonly $FLAGS_FALSE \
-  "Use binary packages only for the board toolchain."
-DEFINE_integer jobs "${NUM_JOBS}" \
-  "How many packages to build in parallel at maximum."
-DEFINE_boolean rebuild "${FLAGS_FALSE}" \
-  "Don't automatically rebuild dependencies."
-DEFINE_boolean skip_chroot_upgrade "${FLAGS_FALSE}" \
-  "Don't run the chroot upgrade automatically; use with care."
-DEFINE_boolean skip_toolchain_update "${FLAGS_FALSE}" \
-  "Don't update toolchain automatically."
 
 # Parse command line
 FLAGS "$@" || exit 1

From 81ee5389c04b655de738fbeed773f595d1932f55 Mon Sep 17 00:00:00 2001
From: Michael Marineau <michael.marineau@coreos.com>
Date: Wed, 3 Feb 2016 17:43:11 -0800
Subject: [PATCH 6/8] build_packages: accept package names as an argument

---
 build_packages | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/build_packages b/build_packages
index a2820fdf40..7fda96034f 100755
--- a/build_packages
+++ b/build_packages
@@ -56,6 +56,12 @@ eval set -- "${FLAGS_ARGV}"
 # Die on any errors.
 switch_to_strict_mode
 
+# TODO(marineam): specify the default top-level ebuild in the portage profile.
+# I could have sworn we did that or similar but maybe got lost at some point.
+if [[ $# -eq 0 ]]; then
+  set -- @system coreos-devel/board-packages
+fi
+
 if [[ -z "${FLAGS_board}" ]]; then
   echo "Error: --board is required."
   exit 1
@@ -200,8 +206,7 @@ break_dep_loop sys-apps/util-linux udev,systemd sys-apps/systemd cryptsetup
 break_dep_loop sys-apps/systemd cryptsetup
 
 info "Merging board packages now"
-sudo -E "${EMERGE_CMD[@]}" "${EMERGE_FLAGS[@]}" \
-    @system coreos-devel/board-packages
+sudo -E "${EMERGE_CMD[@]}" "${EMERGE_FLAGS[@]}" "$@"
 
 info "Removing obsolete packages"
 sudo -E "${EMERGE_CMD[@]}" --quiet --depclean @unavailable

From a3fceb195758d7cce78f1ee3923831c4826a0c87 Mon Sep 17 00:00:00 2001
From: Michael Marineau <michael.marineau@coreos.com>
Date: Wed, 3 Feb 2016 18:10:00 -0800
Subject: [PATCH 7/8] update_chroot: cleanup flags, include all in usage

---
 update_chroot | 24 +++++++++---------------
 1 file changed, 9 insertions(+), 15 deletions(-)

diff --git a/update_chroot b/update_chroot
index ca3bfa4163..665e22a82e 100755
--- a/update_chroot
+++ b/update_chroot
@@ -13,27 +13,21 @@ assert_inside_chroot "$@"
 # Do not run as root
 assert_not_root_user
 
-# Developer-visible flags.
-DEFINE_boolean usepkg $FLAGS_TRUE \
-  "Use binary packages to bootstrap."
-DEFINE_boolean getbinpkg $FLAGS_TRUE \
+DEFINE_boolean usepkg "${FLAGS_TRUE}" \
+  "Use binary packages when possible."
+DEFINE_boolean getbinpkg "${FLAGS_TRUE}" \
   "Download binary packages from remote repository."
+DEFINE_integer jobs "${NUM_JOBS}" \
+  "How many packages to build in parallel at maximum."
+DEFINE_boolean skip_toolchain_update "${FLAGS_FALSE}" \
+  "Don't update the toolchains."
+DEFINE_string toolchain_boards "" \
+  "Extra toolchains to setup for the specified boards."
 
 FLAGS_HELP="usage: $(basename $0) [flags]
 Performs an update of the chroot. This script is called as part of
 build_packages, so there is typically no need to call this script directly.
 "
-show_help_if_requested "$@"
-
-# The following options are advanced options, only available to those willing
-# to read the source code. They are not shown in help output, since they are
-# not needed for the typical developer workflow.
-DEFINE_integer jobs "${NUM_JOBS}" \
-  "How many packages to build in parallel at maximum."
-DEFINE_boolean skip_toolchain_update $FLAGS_FALSE \
-  "Don't update the toolchains."
-DEFINE_string toolchain_boards "" \
-  "Extra toolchains to setup for the specified boards."
 
 # Parse command line flags
 FLAGS "$@" || exit 1

From d327840ce827dd327f3dd3b139dbf5c5ed5b11fb Mon Sep 17 00:00:00 2001
From: Michael Marineau <michael.marineau@coreos.com>
Date: Wed, 3 Feb 2016 18:20:37 -0800
Subject: [PATCH 8/8] *: add --usepkgonly flag to avoid building from source

---
 build_packages | 52 ++++++++++++++++++++++++++++++++++++++------------
 setup_board    | 23 +++++++++++++++++++++-
 update_chroot  | 25 +++++++++++++++++++++---
 3 files changed, 84 insertions(+), 16 deletions(-)

diff --git a/build_packages b/build_packages
index 7fda96034f..39f8b8a914 100755
--- a/build_packages
+++ b/build_packages
@@ -16,6 +16,8 @@ DEFINE_string board "${DEFAULT_BOARD}" \
   "The board to build packages for."
 DEFINE_boolean usepkg "${FLAGS_TRUE}" \
   "Use binary packages when possible."
+DEFINE_boolean usepkgonly "${FLAGS_FALSE}" \
+  "Only use/download binary packages. Implies --noworkon"
 DEFINE_boolean getbinpkg "${FLAGS_TRUE}" \
   "Download binary packages from remote repository."
 DEFINE_string getbinpkgver "" \
@@ -67,6 +69,19 @@ if [[ -z "${FLAGS_board}" ]]; then
   exit 1
 fi
 
+if [[ "${FLAGS_usepkgonly}" -eq "${FLAGS_TRUE}" ]]; then
+  for flag in usepkg getbinpkg; do
+    fvar="FLAGS_${flag}"
+    if [[ "${!fvar}" -ne "${FLAGS_TRUE}" ]]; then
+      die_notrace "--usepkgonly is incompatible with --no${flag}"
+    fi
+  done
+  if [[ "${FLAGS_rebuild}" -eq "${FLAGS_TRUE}" ]]; then
+    die_notrace "--usepkgonly is incompatible with --rebuild"
+  fi
+  FLAGS_workon="${FLAGS_FALSE}"
+fi
+
 check_gsutil_opts
 
 CHROMITE_BIN="${GCLIENT_ROOT}/chromite/bin"
@@ -75,6 +90,11 @@ CHROMITE_BIN="${GCLIENT_ROOT}/chromite/bin"
 UPDATE_ARGS=( --regen_configs )
 if [ "${FLAGS_usepkg}" -eq "${FLAGS_TRUE}" ]; then
   UPDATE_ARGS+=( --usepkg )
+  if [[ "${FLAGS_usepkgonly}" -eq "${FLAGS_TRUE}" ]]; then
+    UPDATE_ARGS+=( --usepkgonly )
+  else
+    UPDATE_ARGS+=( --nousepkgonly )
+  fi
   if [[ "${FLAGS_getbinpkg}" -eq "${FLAGS_TRUE}" ]]; then
     UPDATE_ARGS+=( --getbinpkg )
   else
@@ -121,15 +141,19 @@ EMERGE_CMD+=( ${EXTRA_BOARD_FLAGS} )
 if [[ "${FLAGS_usepkg}" -eq "${FLAGS_TRUE}" ]]; then
   # Use binary packages. Include all build-time dependencies,
   # so as to avoid unnecessary differences between source
-  # and binary builds.
-  EMERGE_FLAGS+=( --usepkg --with-bdeps y )
+  # and binary builds except for --usepkgonly for speed.
+  if [[ "${FLAGS_usepkgonly}" -eq "${FLAGS_TRUE}" ]]; then
+    EMERGE_FLAGS+=( --usepkgonly )
+  else
+    EMERGE_FLAGS+=( --usepkg --with-bdeps y )
+
+    # Only update toolchain when binpkgs are available.
+    EMERGE_FLAGS+=( $(get_binonly_args) )
+    REBUILD_FLAGS+=( $(get_binonly_args) )
+  fi
   if [[ "${FLAGS_getbinpkg}" -eq "${FLAGS_TRUE}" ]]; then
       EMERGE_FLAGS+=( --getbinpkg )
   fi
-
-  # Only update toolchain when binpkgs are available.
-  EMERGE_FLAGS+=( $(get_binonly_args) )
-  REBUILD_FLAGS+=( $(get_binonly_args) )
 fi
 
 if [[ "${FLAGS_jobs}" -ne -1 ]]; then
@@ -199,11 +223,13 @@ break_dep_loop() {
   sudo rm -f "${flag_file}"
 }
 
-# util-linux[udev] -> virtual->udev -> systemd -> util-linux
-break_dep_loop sys-apps/util-linux udev,systemd sys-apps/systemd cryptsetup
+if [[ "${FLAGS_usepkgonly}" -eq "${FLAGS_FALSE}" ]]; then
+  # util-linux[udev] -> virtual->udev -> systemd -> util-linux
+  break_dep_loop sys-apps/util-linux udev,systemd sys-apps/systemd cryptsetup
 
-# systemd[cryptsetup] -> cryptsetup -> lvm2 -> virtual/udev -> systemd
-break_dep_loop sys-apps/systemd cryptsetup
+  # systemd[cryptsetup] -> cryptsetup -> lvm2 -> virtual/udev -> systemd
+  break_dep_loop sys-apps/systemd cryptsetup
+fi
 
 info "Merging board packages now"
 sudo -E "${EMERGE_CMD[@]}" "${EMERGE_FLAGS[@]}" "$@"
@@ -211,8 +237,10 @@ sudo -E "${EMERGE_CMD[@]}" "${EMERGE_FLAGS[@]}" "$@"
 info "Removing obsolete packages"
 sudo -E "${EMERGE_CMD[@]}" --quiet --depclean @unavailable
 
-if "portageq-${BOARD}" list_preserved_libs "${BOARD_ROOT}" >/dev/null; then
-  sudo -E "${EMERGE_CMD[@]}" "${REBUILD_FLAGS[@]}" @preserved-rebuild
+if [[ "${FLAGS_usepkgonly}" -eq "${FLAGS_TRUE}" ]]; then
+  if "portageq-${BOARD}" list_preserved_libs "${BOARD_ROOT}" >/dev/null; then
+    sudo -E "${EMERGE_CMD[@]}" "${REBUILD_FLAGS[@]}" @preserved-rebuild
+  fi
 fi
 
 info "Checking build root"
diff --git a/setup_board b/setup_board
index aa2a1e5d42..c10ca694e6 100755
--- a/setup_board
+++ b/setup_board
@@ -21,6 +21,8 @@ DEFINE_boolean force "${FLAGS_FALSE}" \
   "Force re-creating board root."
 DEFINE_boolean usepkg "${FLAGS_TRUE}" \
   "Use binary packages when possible."
+DEFINE_boolean usepkgonly "${FLAGS_FALSE}" \
+  "Only use/download binary packages."
 DEFINE_boolean getbinpkg "${FLAGS_TRUE}" \
   "Download binary packages from remote repository."
 DEFINE_string getbinpkgver "" \
@@ -135,12 +137,26 @@ if [ -z "$FLAGS_board" ] ; then
   exit 1
 fi
 
+if [[ "${FLAGS_usepkgonly}" -eq "${FLAGS_TRUE}" ]]; then
+  for flag in usepkg getbinpkg; do
+    fvar="FLAGS_${flag}"
+    if [[ "${!fvar}" -ne "${FLAGS_TRUE}" ]]; then
+      die_notrace "--usepkgonly is incompatible with --no${flag}"
+    fi
+  done
+fi
+
 get_board_and_variant $FLAGS_board $FLAGS_variant
 
 # Before we can run any tools, we need to update chroot
 UPDATE_ARGS="--toolchain_boards=${BOARD}"
 if [ "${FLAGS_usepkg}" -eq "${FLAGS_TRUE}" ]; then
   UPDATE_ARGS+=" --usepkg"
+  if [[ "${FLAGS_usepkgonly}" -eq "${FLAGS_TRUE}" ]]; then
+    UPDATE_ARGS+=" --usepkgonly"
+  else
+    UPDATE_ARGS+=" --usepkgonly"
+  fi
   if [[ "${FLAGS_getbinpkg}" -eq "${FLAGS_TRUE}" ]]; then
     UPDATE_ARGS+=" --getbinpkg "
   else
@@ -284,7 +300,12 @@ if [[ ${FLAGS_regen_configs} -eq ${FLAGS_FALSE} ]]; then
   if [[ "${FLAGS_usepkg}" -eq "${FLAGS_TRUE}"  && \
         "${FLAGS_getbinpkg}" -eq "${FLAGS_TRUE}" ]]
   then
-    EMERGE_FLAGS+=" --usepkg --getbinpkg"
+    if [[ "${FLAGS_usepkgonly}" -eq "${FLAGS_TRUE}" ]]; then
+      EMERGE_FLAGS+=" --usepkgonly"
+    else
+      EMERGE_FLAGS+=" --usepkg"
+    fi
+    EMERGE_FLAGS+=" --getbinpkg"
     EMERGE_TOOLCHAIN_FLAGS+=" --usepkgonly --getbinpkg"
   else
     # When binary packages are disabled we need to make sure the cross
diff --git a/update_chroot b/update_chroot
index 665e22a82e..d0a9b35af2 100755
--- a/update_chroot
+++ b/update_chroot
@@ -17,6 +17,10 @@ DEFINE_boolean usepkg "${FLAGS_TRUE}" \
   "Use binary packages when possible."
 DEFINE_boolean getbinpkg "${FLAGS_TRUE}" \
   "Download binary packages from remote repository."
+DEFINE_boolean usepkgonly "${FLAGS_FALSE}" \
+  "Only use/download binary packages. Implies --noworkon"
+DEFINE_boolean workon "${FLAGS_TRUE}" \
+  "Automatically rebuild updated cros-workon packages."
 DEFINE_integer jobs "${NUM_JOBS}" \
   "How many packages to build in parallel at maximum."
 DEFINE_boolean skip_toolchain_update "${FLAGS_FALSE}" \
@@ -37,6 +41,16 @@ eval set -- "${FLAGS_ARGV}"
 # so will die prematurely if 'switch_to_strict_mode' is specified before now.
 switch_to_strict_mode
 
+if [[ "${FLAGS_usepkgonly}" -eq "${FLAGS_TRUE}" ]]; then
+  for flag in usepkg getbinpkg; do
+    fvar="FLAGS_${flag}"
+    if [[ "${!fvar}" -ne "${FLAGS_TRUE}" ]]; then
+      die_notrace "--usepkgonly is incompatible with --no${flag}"
+    fi
+  done
+  FLAGS_workon="${FLAGS_FALSE}"
+fi
+
 . "${BUILD_LIBRARY_DIR}/toolchain_util.sh"
 
 PORTAGE_STABLE_OVERLAY="${REPO_ROOT}/src/third_party/portage-stable"
@@ -166,6 +180,9 @@ EMERGE_FLAGS="-uNv --with-bdeps=y --select"
 REBUILD_FLAGS=""
 if [ "${FLAGS_usepkg}" -eq "${FLAGS_TRUE}" ]; then
   EMERGE_FLAGS="${EMERGE_FLAGS} --usepkg"
+  if [[ "${FLAGS_usepkgonly}" -eq "${FLAGS_TRUE}" ]]; then
+    EMERGE_FLAGS+=" --usepkgonly"
+  fi
   if [ "${FLAGS_getbinpkg}" -eq "${FLAGS_TRUE}" ]; then
     EMERGE_FLAGS="${EMERGE_FLAGS} --getbinpkg"
   fi
@@ -210,9 +227,11 @@ fi
 
 # Build cros_workon packages when they are changed.
 CHROMITE_BIN="${GCLIENT_ROOT}/chromite/bin"
-for pkg in $("${CHROMITE_BIN}/cros_list_modified_packages" --host); do
-  EMERGE_FLAGS+=" --reinstall-atoms=${pkg} --usepkg-exclude=${pkg}"
-done
+if [ "${FLAGS_workon}" -eq "${FLAGS_TRUE}" ]; then
+  for pkg in $("${CHROMITE_BIN}/cros_list_modified_packages" --host); do
+    EMERGE_FLAGS+=" --reinstall-atoms=${pkg} --usepkg-exclude=${pkg}"
+  done
+fi
 
 # Second pass, update everything else.
 EMERGE_FLAGS+=" --deep"