[kvm-unit-tests PATCH v4 3/8] migration: use a more robust way to wait for background job

[Nicholas Piggin]

Starting a pipeline of jobs in the background does not seem to have
a simple way to reliably find the pid of a particular process in the
pipeline (because not all processes are started when the shell
continues to execute).

The way PID of QEMU is derived can result in a failure waiting on a
PID that is not running. This is easier to hit with subsequent
multiple-migration support. Changing this to use $! by swapping the
pipeline for a fifo is more robust.

Reviewed-by: Thomas Huth <thuth at redhat.com>
Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
---
 scripts/arch-run.bash | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/scripts/arch-run.bash b/scripts/arch-run.bash
index c1dd67ab..9a5aaddc 100644
--- a/scripts/arch-run.bash
+++ b/scripts/arch-run.bash
@@ -130,19 +130,22 @@ run_migration ()
 	fi
 
 	trap 'trap - TERM ; kill 0 ; exit 2' INT TERM
-	trap 'rm -f ${migout1} ${migsock} ${qmp1} ${qmp2} ${fifo}' RETURN EXIT
+	trap 'rm -f ${migout1} ${migout_fifo1} ${migsock} ${qmp1} ${qmp2} ${fifo}' RETURN EXIT
 
 	migsock=$(mktemp -u -t mig-helper-socket.XXXXXXXXXX)
 	migout1=$(mktemp -t mig-helper-stdout1.XXXXXXXXXX)
+	migout_fifo1=$(mktemp -u -t mig-helper-fifo-stdout1.XXXXXXXXXX)
 	qmp1=$(mktemp -u -t mig-helper-qmp1.XXXXXXXXXX)
 	qmp2=$(mktemp -u -t mig-helper-qmp2.XXXXXXXXXX)
 	fifo=$(mktemp -u -t mig-helper-fifo.XXXXXXXXXX)
 	qmpout1=/dev/null
 	qmpout2=/dev/null
 
+	mkfifo ${migout_fifo1}
 	eval "$@" -chardev socket,id=mon1,path=${qmp1},server=on,wait=off \
-		-mon chardev=mon1,mode=control | tee ${migout1} &
-	live_pid=`jobs -l %+ | grep "eval" | awk '{print$2}'`
+		-mon chardev=mon1,mode=control > ${migout_fifo1} &
+	live_pid=$!
+	cat ${migout_fifo1} | tee ${migout1} &
 
 	# We have to use cat to open the named FIFO, because named FIFO's, unlike
 	# pipes, will block on open() until the other end is also opened, and that
@@ -150,7 +153,7 @@ run_migration ()
 	mkfifo ${fifo}
 	eval "$@" -chardev socket,id=mon2,path=${qmp2},server=on,wait=off \
 		-mon chardev=mon2,mode=control -incoming unix:${migsock} < <(cat ${fifo}) &
-	incoming_pid=`jobs -l %+ | awk '{print$2}'`
+	incoming_pid=$!
 
 	# The test must prompt the user to migrate, so wait for the "migrate" keyword
 	while ! grep -q -i "Now migrate the VM" < ${migout1} ; do
@@ -164,6 +167,10 @@ run_migration ()
 		sleep 1
 	done
 
+	# Wait until the destination has created the incoming and qmp sockets
+	while ! [ -S ${migsock} ] ; do sleep 0.1 ; done
+	while ! [ -S ${qmp2} ] ; do sleep 0.1 ; done
+
 	qmp ${qmp1} '"migrate", "arguments": { "uri": "unix:'${migsock}'" }' > ${qmpout1}
 
 	# Wait for the migration to complete
-- 
2.42.0