tools/packaging: Fix error path in 'kata-deploy-binaries.sh -s'

`make kata-tarball` relies on `kata-deploy-binaries.sh -s` which
silently ignores errors, and you may end up with an incomplete
tarball without noticing it because `make`'s exit status is 0.

`kata-deploy-binaries.sh` does set the `errexit` option and all the
code in the script seems to assume that since it doesn't do error
checking. Unfortunately, bash automatically disables `errexit` when
calling a function from a conditional pipeline, like done in the `-s`
case:

	if [ "${silent}" == true ]; then
		if ! handle_build "${t}" &>"$log_file"; then
                ^^^^^^
           this disables `errexit`

and `handle_build` ends with a `tar tvf` that always succeeds.

Adding error checking all over the place isn't really an option
as it would seriously obfuscate the code. Drop the conditional
pipeline instead and print the final error message from a `trap`
handler on the special ERR signal. This requires the `errtrace`
option as `trap`s aren't propagated to functions by default.

Since all outputs of `handle_build` are redirected to the build
log file, some file descriptor duplication magic is needed for
the handler to be able to write to the orignal stdout and stderr.

Fixes #3757

Signed-off-by: Greg Kurz <groug@kaod.org>

tools/packaging/kata-deploy/local-build/kata-deploy-binaries.sh

@@ -8,6 +8,7 @@
 set -o errexit
 set -o nounset
 set -o pipefail
+set -o errtrace
 
 readonly project="kata-containers"
 
@@ -196,6 +197,18 @@ handle_build() {
 	tar tvf "${tarball_name}"
 }
 
+silent_mode_error_trap() {
+	local stdout="$1"
+	local stderr="$2"
+	local t="$3"
+	local log_file="$4"
+	exec 1>&${stdout}
+	exec 2>&${stderr}
+	error "Failed to build: $t, logs:"
+	cat "${log_file}"
+	exit 1
+}
+
 main() {
 	local build_targets
 	local silent
@@ -248,11 +261,15 @@ main() {
 		(
 			cd "${builddir}"
 			if [ "${silent}" == true ]; then
-				if ! handle_build "${t}" &>"$log_file"; then
-					error "Failed to build: $t, logs:"
-					cat "${log_file}"
-					exit 1
-				fi
+				local stdout
+				local stderr
+				# Save stdout and stderr, to be restored
+				# by silent_mode_error_trap() in case of
+				# build failure.
+				exec {stdout}>&1
+				exec {stderr}>&2
+				trap "silent_mode_error_trap $stdout $stderr $t \"$log_file\"" ERR
+				handle_build "${t}" &>"$log_file"
 			else
 				handle_build "${t}"
 			fi