Re: [kvm-unit-tests PATCH v2 4/9] migration: use a more robust way to wait for background job

On Fri, Feb 02, 2024 at 04:57 PM +1000, Nicholas Piggin [off-list ref] 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>
---

[…snip…]

 
+	# 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

There should be timeout implemented, otherwise we might end in an
endless loop in case of a bug. Or is the global timeout good enough to
handle this situation?

+
 	qmp ${qmp1} '"migrate", "arguments": { "uri": "unix:'${migsock}'" }' > ${qmpout1}
 
 	# Wait for the migration to complete
-- 
2.42.0

-- 
Kind regards / Beste Grüße
   Marc Hartmayer

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