[PATCH] iotests/108: probe loop device setup

[Ilya Leoshkevich <iii@linux.ibm.com>]

Running iotests/108 in a Docker container, that has passwordless sudo
configured, fails with:

    losetup: /home/user/src/qemu/build/scratch/qcow2-file-108/t.qcow2: failed to set up loop device: No such file or directory

because it incorrectly assumes losetup is allowed to do loop device
setup, when in reality it can only list devices.

Fix by probing loop device setup, using the test script as a backing
file. With this, the test is correctly skipped.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 tests/qemu-iotests/108 | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tests/qemu-iotests/108 b/tests/qemu-iotests/108
index 1de718188aa..adbaaf87095 100755
--- a/tests/qemu-iotests/108
+++ b/tests/qemu-iotests/108
@@ -53,7 +53,8 @@ _supported_os Linux
 _unsupported_imgopts 'refcount_bits=\([^1]\|.\([^6]\|$\)\)' data_file
 
 # This test either needs sudo -n losetup or FUSE exports to work
-if sudo -n losetup &>/dev/null; then
+if probe_dev=$(sudo -n losetup -r --show -f "$0" 2>/dev/null); then
+    sudo -n losetup -d "$probe_dev"
     loopdev=true
 else
     loopdev=false
-- 
2.56.0