[PATCH v3 5/9] Move buildchroot mounts into dpkg-base class

[Jan Kiszka <jan.kiszka@siemens.com>]

From: Jan Kiszka <jan.kiszka@siemens.com>

This avoids the unfortunate setup_mounts task which is either not
executed on rebuilds or causes excessive package rebuilds. We just need
ensure prior to switching into the buildchroot that all mount points are
populated. The mounts may race with parallel build, so lock-protect the
check if they are needed and their execution.

Note that the more beautiful syntax using ( flock -n 9; ... ) 9>lockfile
as described in the flock man page does not work in bitbake shell
functions.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---

Changes in v3:
 - use flock instead of unreliable check pattern

 meta/classes/dpkg-base.bbclass                   | 11 ++++++++-
 meta/recipes-devtools/buildchroot/buildchroot.bb | 30 +++---------------------
 2 files changed, 13 insertions(+), 28 deletions(-)

diff --git a/meta/classes/dpkg-base.bbclass b/meta/classes/dpkg-base.bbclass
index a45fbce..895ff26 100644
--- a/meta/classes/dpkg-base.bbclass
+++ b/meta/classes/dpkg-base.bbclass
@@ -2,7 +2,7 @@
 # Copyright (C) 2017 Siemens AG
 
 # Add dependency from buildchroot creation
-do_build[depends] = "buildchroot:do_setup_mounts"
+do_build[depends] = "buildchroot:do_build"
 
 # Add dependency between Isar recipes
 DEPENDS ?= ""
@@ -20,11 +20,20 @@ dpkg_runbuild() {
     die "This should never be called, overwrite it in your derived class"
 }
 
+MOUNT_LOCKFILE = "${TMPDIR}/buildchroot-mount.lock"
+
 # Wrap the function dpkg_runbuild with the bind mount for buildroot
 do_build() {
     mkdir -p ${BUILDROOT}
     sudo mount --bind ${WORKDIR} ${BUILDROOT}
 
+    sudo flock ${MOUNT_LOCKFILE} -c ' \
+        if ! grep -q ${BUILDCHROOT_DIR}/isar-apt /proc/mounts; then \
+            mount --bind ${DEPLOY_DIR_APT}/${DISTRO} ${BUILDCHROOT_DIR}/isar-apt; \
+            mount -t devtmpfs -o mode=0755,nosuid devtmpfs ${BUILDCHROOT_DIR}/dev; \
+            mount -t proc none ${BUILDCHROOT_DIR}/proc; \
+        fi'
+
     dpkg_runbuild
 
     sudo umount ${BUILDROOT} 2>/dev/null || true
diff --git a/meta/recipes-devtools/buildchroot/buildchroot.bb b/meta/recipes-devtools/buildchroot/buildchroot.bb
index 570c0ad..cd91228 100644
--- a/meta/recipes-devtools/buildchroot/buildchroot.bb
+++ b/meta/recipes-devtools/buildchroot/buildchroot.bb
@@ -60,7 +60,9 @@ do_build() {
         -e 's|##DIR_HOOKS##|./'"$WORKDIR_REL"'/hooks_multistrap|g' \
            "${WORKDIR}/multistrap.conf.in" > "${WORKDIR}/multistrap.conf"
 
-    do_setup_mounts
+    sudo mount --bind ${DEPLOY_DIR_APT}/${DISTRO} ${BUILDCHROOT_DIR}/isar-apt
+    sudo mount -t devtmpfs -o mode=0755,nosuid devtmpfs ${BUILDCHROOT_DIR}/dev
+    sudo mount -t proc none ${BUILDCHROOT_DIR}/proc
 
     # Create root filesystem
     sudo -E multistrap -a ${DISTRO_ARCH} -d "${BUILDCHROOT_DIR}" -f "${WORKDIR}/multistrap.conf"
@@ -70,30 +72,4 @@ do_build() {
 
     # Configure root filesystem
     sudo chroot ${BUILDCHROOT_DIR} /configscript.sh
-
-    do_cleanup_mounts
-}
-
-# Invalidate stamp for do_setup_mounts before each build start.
-# This will guarantee that this function will be executed once
-# per build.
-python __anonymous() {
-    stamp = d.getVar("STAMP") + ".do_setup_mounts." + d.getVarFlag("do_setup_mounts", 'stamp-extra-info')
-    os.remove(stamp) if os.path.exists(stamp) else None
-}
-
-do_setup_mounts[stamp-extra-info] = "${DISTRO}-${DISTRO_ARCH}"
-
-do_setup_mounts() {
-    sudo mount --bind ${DEPLOY_DIR_APT}/${DISTRO} ${BUILDCHROOT_DIR}/isar-apt
-    sudo mount -t devtmpfs -o mode=0755,nosuid devtmpfs ${BUILDCHROOT_DIR}/dev
-    sudo mount -t proc none ${BUILDCHROOT_DIR}/proc
-}
-
-addtask setup_mounts after do_build
-
-do_cleanup_mounts() {
-    sudo umount ${BUILDCHROOT_DIR}/isar-apt 2>/dev/null || true
-    sudo umount ${BUILDCHROOT_DIR}/dev 2>/dev/null || true
-    sudo umount ${BUILDCHROOT_DIR}/proc 2>/dev/null || true
 }
-- 
2.13.6