[kvm-unit-tests PATCH v3 3/8] migration: use a more robust way to wait for background job

Nicholas Piggin
2024-02-09T07:02:21Z

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.

Signed-off-by: Nicholas Piggin <npiggin@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 1e903e83..3689d7c2 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