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

Thomas Huth
2024-02-09T07:43:43Z

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 <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

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