v4 won't (re) start if _.vsm preexists -- starts fine if deleted 1st

[grantksupport at operamail.com]

Hi,

Still working on my v3->v4 upgrade.

I've noticed that while v3 stopped/started without any problems, my v4
instance starts -- but only (?) if there's no previous "_.vsm" lying
around.

Here's what I'm seeing:

systemctl start varnish-custom.service
	-> RUNS/OK
ls -al /usr/local/var/varnish/TEST/
	total 82M
	drwxrwxrwt  2 root    root      80 May  5 06:55 ./
	drwxrwxr-x+ 3 grant   users   4.0K May  5 06:05 ../
	-rwxr-xr-x  1 nobody  nogroup  77K May  5 06:55 vcl.vLB_IZSL.so*
	-rw-r--r--  1 root    root     81M May  5 06:55 _.vsm

systemctl stop varnish-custom.service
ls -al /usr/local/var/varnish/TEST/
	total 120M
	drwxrwxrwt  2 root    root    80 May  5 06:56 ./
	drwxrwxr-x+ 3 grant   users 4.0K May  5 06:05 ../
	-rw-r--r--  1 root    root   81M May  5 06:55 _.vsm
	-rw-r--r--  1 root    root   39M May  5 06:56 _.vsm.13175

systemctl start varnish-custom.service
	Job for varnish-custom.service failed. See 'systemctl status
	varnish-custom.service' and 'journalctl -xn' for details.

systemctl stop varnish-custom.service
systemctl start varnish-custom.service
	Job for varnish-custom.service failed. See 'systemctl status
	varnish-custom.service' and 'journalctl -xn' for details.

systemctl stop varnish-custom.service
ls -al /usr/local/var/varnish/TEST/
	total 120M
	drwxrwxrwt  2 root    root    80 May  5 06:56 ./
	drwxrwxr-x+ 3 grant   users 4.0K May  5 06:05 ../
	-rw-r--r--  1 root    root   81M May  5 06:55 _.vsm
	-rw-r--r--  1 root    root   39M May  5 06:56 _.vsm.13175

rm -f /usr/local/var/varnish/TEST/_.vsm*
ls -al /usr/local/var/varnish/TEST/
	total 4.0K
	drwxrwxrwt  2 root    root    40 May  5 07:01 ./
	drwxrwxr-x+ 3 grant   users 4.0K May  5 06:05 ../

systemctl start varnish-custom.service
	-> RUNS/OK
ls -al /usr/local/var/varnish/TEST/
	total 82M
	drwxrwxrwt  2 root    root      80 May  5 07:03 ./
	drwxrwxr-x+ 3 grant   users   4.0K May  5 06:05 ../
	-rwxr-xr-x  1 nobody  nogroup  77K May  5 07:03 vcl.qH7WsF0n.so*
	-rw-r--r--  1 root    root     81M May  5 07:03 _.vsm

Reading here,
https://www.varnish-cache.org/docs/trunk/reference/vsm.html, iiuc (?)
the vsm should be cleared on stop?

I can reproduce this ^^^ on two different machines, so if it's something
I'm (not) doing, I'm at least consistent.

Grant