cgroups test: log a warning if the scheduler does not appear to be cfq

Of the schedulers we compile, only cfq supports the block I/O weighting
feature that is exercised by test_blkio_weights_random_read and
test_blkio_weights_sequential_read.

Related to <https://bugs.apertis.org/show_bug.cgi?id=635

>

Reviewed-by: Philip Withnall <philip.withnall@collabora.co.uk>
Signed-off-by: Simon McVittie <simon.mcvittie@collabora.co.uk>
Differential Revision: https://phabricator.apertis.org/D2165

cgroups/automated/run-test.sh

@@ -142,6 +142,18 @@ _write_random_files() {
 
 # Setup for blkio tests
 _setup_blkio() {
+    root_partition="$(grep ' / ' /proc/self/mounts | cut -d' ' -f1 | grep -v '^rootfs$')"
+    root_drive="$(echo "${root_partition}" | sed -e 's,p\?[0-9]\+$,,')"
+    root_drive="${root_drive#/dev/}"
+    head -v /sys/block/${root_drive}/queue/scheduler 2>&1 | sed -e 's/^/# /'
+    case "$(cat /sys/block/${root_drive}/queue/scheduler)" in
+        (*\[cfq\]*)
+            ;;
+        (*)
+            echo "WARNING: Block device scheduler does not appear to be cfq."
+            echo "This is probably not going to work, but trying it anyway..."
+    esac
+
     _reset_cgroup blkio
     # Set the resource allocation proportion
     echo "# Configuring $MID_CG cgroup with blkio.weight = 1000"