[OE-core] [PATCH] image: Attempt to work around do_image_complete race

[Mike Crowe]

If two do_image_complete tasks run in parallel they risk both trying to put
their image into ${DEPLOY_DIR_IMAGE} at the same time. Both will contain a
README_-_DO_NOT_DELETE_FILES_IN_THIS_DIRECTORY.txt file. In theory this
should be safe because "cp -alf" will just cause one to overwrite the
other. Unfortunately, coreutils cp also has a race which means that if one
copy creates the file at just the wrong point the other will fail with:

 cp: cannot create hard link ‘..../tmp-glibc/deploy/images/pantera/README_-_DO_NOT_DELETE_FILES_IN_THIS_D.txt’ to ‘..../tmp-glibc/work/rage_against-oe-linux-gnueabi/my-own-image/1.0-r0/deploy-my-own-image-complete/README_-_DO_NOT_DELETE_FILES_IN_THIS_DIRECTORY.txt’: File exists

The coreutils bug has been reported and fixed upstream as
https://debbugs.gnu.org/cgi/bugreport.cgi?bug=25680 , but it will take
a while for host distributions to catch up.

In the meantime, let's try and avoid the race altogether by causing
sstate.bbclass:sstate_install to take a lock file in
${DEPLOY_DIR_IMAGE} whilst writing. This lock is probably a bit broad,
but it's better than the build failing.

Signed-off-by: Mike Crowe <mac at mcrowe.com>
---
 meta/classes/image.bbclass | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/meta/classes/image.bbclass b/meta/classes/image.bbclass
index b5a4fb4a33..5c2f183446 100644
--- a/meta/classes/image.bbclass
+++ b/meta/classes/image.bbclass
@@ -298,6 +298,10 @@ SSTATE_SKIP_CREATION_task-image-complete = '1'
 do_image_complete[sstate-inputdirs] = "${IMGDEPLOYDIR}"
 do_image_complete[sstate-outputdirs] = "${DEPLOY_DIR_IMAGE}"
 do_image_complete[stamp-extra-info] = "${MACHINE}"
+# Defend against copying two different images to ${DEPLOY_DIR_IMAGE}
+# at the same time because they risk both trying to create
+# README_-_DO_NOT_DELETE_FILES_IN_THIS_DIRECTORY.txt at the same time.
+do_image_complete[sstate-lockfile-shared] = "${DEPLOY_DIR_IMAGE}/image-complete-output.lock"
 addtask do_image_complete after do_image before do_build
 
 # Add image-level QA/sanity checks to IMAGE_QA_COMMANDS
-- 
2.12.0.rc0