block/012: add comment explaning second --setro

Closes #73.

Signed-off-by: Omar Sandoval <osandov@fb.com>

diff --git a/tests/block/012 b/tests/block/012
index 3b0bed5b789a8bf2d3f1150f72c4a2f771528f0b..c92f5b4b8dd23bf077d6252fae67bfad6cabe79f 100755 (executable)
--- a/tests/block/012
+++ b/tests/block/012
@@ -20,6 +20,7 @@ test_device() {
        xfs_io -c "pwrite -w -S 0xaa -b 2M 0 2M" -d "$TEST_DEV" >>"$FULL"
        dd if="$TEST_DEV" bs=2M count=1 2>>"$FULL" | hexdump
        blockdev --setro "$TEST_DEV"
+       # It is valid to set a device that is already read-only to read-only.
        blockdev --setro "$TEST_DEV"
        blockdev --getro "$TEST_DEV"
        # writes should fail while device is read-only