test: Fix memory/passt tests, --netns-only is not a valid option for passt

This used to work on my setup as I kept reusing an old mbuto
(initramfs) image, but since commit 65923ba798 ("conf: Accept
duplicate and conflicting options, the last one wins"), --netns-only
is, as originally intended, a pasta-only option.

I had used --netns-only, here, to prevent passt from trying to detach
its own user namespace, which is not permitted as we're in a chroot,
see unshare(2). In turn, we need the chroot because passt can't pivot
root directly into its own empty filesystem using an initramfs.

Use switch_root into the tmpfs mountpoint instead of chroot, so that
we can still detach user namespaces.

Note that in the mbuto images, we can't switch to nobody as we have
no password entries at all, so we need to detach a further user
namespace before starting passt, to trick passt into running as UID
0.

Given the new sequence, it's now more convenient to directly switch
to a detached network namespace as well, which means we need to move
the initialisation of the dummy network from the init script into the
test script.

Reported-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Tested-by: David Gibson <david@gibson.dropbear.id.au>

test/memory/passt

@@ -44,7 +44,7 @@ endef
 def	start_stop_diff
 guest	sed /proc/slabinfo -ne 's/^\([^ ]* *[^ ]* *[^ ]* *[^ ]*\).*/\\\1/p' > /tmp/slabinfo.before
 guest	cat /proc/meminfo > /tmp/meminfo.before
-guest	/bin/passt.avx2 -l /tmp/log -s /tmp/sock -P /tmp/pid __OPTS__ --netns-only
+guest	/bin/passt.avx2 -l /tmp/log -s /tmp/sock -P /tmp/pid __OPTS__
 sleep	2
 guest	cat /proc/meminfo > /tmp/meminfo.after
 guest	sed /proc/slabinfo -ne 's/^\([^ ]* *[^ ]* *[^ ]* *[^ ]*\).*/\\\1/p' > /tmp/slabinfo.after
@@ -78,9 +78,16 @@ guest	mount -o bind /proc /test/proc
 guest	mount -o bind /dev /test/dev
 guest	cp -Lr /bin /lib /lib64 /usr /sbin /test/
 
+guest	exec switch_root /test /bin/sh
+
 guest	ulimit -Hn 300000
-guest	unshare -rUm -R /test
+guest	unshare -rUn
-guest	chroot .
+guest	ip link add eth0 type dummy
+guest	ip link set eth0 up
+guest	ip address add 192.0.2.2/24 dev eth0
+guest	ip address add 2001:db8::2/64 dev eth0
+guest	ip route add default via 192.0.2.1
+guest	ip -6 route add default via 2001:db8::1 dev eth0
 
 guest	meminfo_size() { grep "^$2:" $1 | tr -s ' ' | cut -f2 -d ' '; }
 guest	meminfo_diff() { echo $(( $(meminfo_size $2 $3) - $(meminfo_size $1 $3) )); }

test/passt.mem.mbuto

@@ -12,7 +12,7 @@
 
 PROGS="${PROGS:-ash,dash,bash chmod ip mount insmod mkdir ln cat chmod modprobe
        grep mknod sed chown sleep bc ls ps mount unshare chroot cp kill diff
-       head tail sort tr tee cut nm which}"
+       head tail sort tr tee cut nm which switch_root}"
 
 KMODS="${KMODS:- dummy}"
 
@@ -29,13 +29,6 @@ COPIES="${COPIES} ../passt.avx2,/bin/passt.avx2"
 FIXUP="${FIXUP}"'
 ln -s /bin /usr/bin
 chmod 777 /tmp
-ip link add eth0 type dummy
-ip link set eth0 up
-ip address add 192.0.2.2/24 dev eth0
-ip address add 2001:db8::2/64 dev eth0
-ip route add default via 192.0.2.1
-ip -6 route add default via 2001:db8::1 dev eth0
-sleep 2
 sh +m
 '