From ce463670f554b4bb121ce4953c869bfededc714c Mon Sep 17 00:00:00 2001
From: Chunjie Zhu <chunjie.zhu@cloud.com>
Date: Fri, 9 Jan 2026 15:43:25 +0800
Subject: [PATCH] CA-395093: sync between tapback slave process and xenopsd

Signed-off-by: Chunjie Zhu <chunjie.zhu@cloud.com>
---
 ocaml/xenopsd/scripts/block | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/ocaml/xenopsd/scripts/block b/ocaml/xenopsd/scripts/block
index a622f922289..ed825cb8979 100755
--- a/ocaml/xenopsd/scripts/block
+++ b/ocaml/xenopsd/scripts/block
@@ -15,6 +15,25 @@ syslog ()
 	logger -tscripts-block "$*"
 }
 
+wait_tapback_ready()
+{
+	local statefile="/var/run/tapback.${DOMID}.statefile"
+	while true; do
+		if [[ -f "$statefile" ]]; then
+			content=$(cat "$statefile")
+			if [[ "$content" == *"ping"* ]]; then
+				syslog "${XENBUS_PATH}: tapback ready"
+				break
+			fi
+		fi
+		syslog "${XENBUS_PATH}: tapback not ready"
+		sleep 1
+	done
+	syslog "${XENBUS_PATH}: signal tapback to continue"
+	echo -n "pong" > "$statefile.tmp"
+	mv "$statefile.tmp" "$statefile"
+}
+
 case "$1" in
 add)
 	if [ "$XENBUS_PREFIX" = "" ]; then
@@ -27,6 +46,8 @@ add)
 		if [ "$TYPE" != "9pfs" ]; then
 			if [[ $params =~ nbd:unix:([^:]*) ]]
 			then
+				# tapback slave process should be ready to process xenstore watch event
+				wait_tapback_ready
 				physical_device_path=$(readlink -f ${BASH_REMATCH[1]})
 				syslog "${XENBUS_PATH}: physical-device-path=${physical_device_path}"
 				xenstore-exists "${XENBUS_PATH}/physical-device-path"