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

[Thomas Huth]

On 09/02/2024 08.01, Nicholas Piggin wrote:

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 <npig...@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

Reviewed-by: Thomas Huth <th...@redhat.com>