test/system: Use correct device for I/O limit tests

The tests were incorrectly using `/dev/zero`.  These options are
intended to set I/O limits on specific block devices.

The test already sets up a loopback device, so reuse it.

Signed-off-by: Giuseppe Scrivano <[email protected]>

Author: giuseppe

test/system/030-run.bats

@@ -1123,18 +1123,24 @@ EOF
 @test "podman run --device-read-bps" {
     skip_if_rootless "cannot use this flag in rootless mode"
 
+    if test \! -e /dev/nullb0; then
+        skip "/dev/nullb0 not present, use 'modprobe null_blk nr_devices=1' to create it"
+    fi
+
     local cid
+    local dev_maj_min=$(stat -c %Hr:%Lr /dev/nullb0)
+
     # this test is a triple check on blkio flags since they seem to sneak by the tests
     if is_cgroupsv2; then
-        run_podman run -dt --device-read-bps=/dev/zero:1M $IMAGE top
+        run_podman run -dt --device-read-bps=/dev/nullb0:1M $IMAGE top
         cid=$output
         run_podman exec -it $output cat /sys/fs/cgroup/io.max
-        is "$output" ".*1:5 rbps=1048576 wbps=max riops=max wiops=max" "throttle devices passed successfully.*"
+        is "$output" ".*$dev_maj_min rbps=1048576 wbps=max riops=max wiops=max" "throttle devices passed successfully.*"
     else
-        run_podman run -dt --device-read-bps=/dev/zero:1M $IMAGE top
+        run_podman run -dt --device-read-bps=/dev/nullb0:1M $IMAGE top
         cid=$output
         run_podman exec -it $output cat /sys/fs/cgroup/blkio/blkio.throttle.read_bps_device
-        is "$output" ".*1:5 1048576" "throttle devices passed successfully.*"
+        is "$output" ".*$dev_maj_min 1048576" "throttle devices passed successfully.*"
     fi
     run_podman container rm -f -t0 $cid
 }

test/system/280-update.bats

@@ -63,10 +63,10 @@ memory-reservation  =           400M | 2 | $mm.soft_limit_in_bytes  = 419430400
 blkio-weight        =            321 | - | -                                       | io.bfq.weight   = default 321 $lomajmin 98
 blkio-weight-device = $LOOPDEVICE:98 | - | -                                       | io.bfq.weight   = default 321 $lomajmin 98
 
-device-read-bps     = /dev/zero:10mb | - | -                                       | io.max          = $devicemax
-device-read-iops    = /dev/zero:2000 | - | -                                       | io.max          = $devicemax
-device-write-bps    = /dev/zero:30mb | - | -                                       | io.max          = $devicemax
-device-write-iops   = /dev/zero:4000 | - | -                                       | io.max          = $devicemax
+device-read-bps     = $LOOPDEVICE:10mb | - | -                                       | io.max          = $devicemax
+device-read-iops    = $LOOPDEVICE:2000 | - | -                                       | io.max          = $devicemax
+device-write-bps    = $LOOPDEVICE:30mb | - | -                                       | io.max          = $devicemax
+device-write-iops   = $LOOPDEVICE:4000 | - | -                                       | io.max          = $devicemax
 "
 
     # Run a container