What happened:

Block device tests running inside the KinD cluster are flaky (kubernetes-csi/csi-driver-host-path#119). It looks like this is because the Docker container in which kubelet runs has a static copy of the host's /dev. In devfs, new loop devices are added by the kernel as needed. But inside the container only those /dev/loop* devices are available which existed already on the host when the container was created, causing losetup to fail:

losetup: /tmp/testfile: failed to set up loop device: No such file or directory

What you expected to happen:

/dev needs to be shared with the host. This isn't nice from a security perspective, but I don't see another solution.

How to reproduce it (as minimally and precisely as possible):

Create a KinD cluster, pick one container with docker ps, then run losetup repeatedly:

$ docker exec f049e80f378a sh -c 'ls /dev/loop*'
/dev/loop-control
/dev/loop0
/dev/loop1
/dev/loop2
/dev/loop3
/dev/loop4
/dev/loop5
/dev/loop6
/dev/loop7
$ docker exec f049e80f378a sh -c 'truncate -s 1G /tmp/testfile; losetup -f --show /tmp/testfile'
/dev/loop0
....
$ docker exec f049e80f378a sh -c 'truncate -s 1G /tmp/testfile; losetup -f --show /tmp/testfile'
/dev/loop7
$ docker exec f049e80f378a sh -c 'truncate -s 1G /tmp/testfile; losetup -f --show /tmp/testfile'
losetup: /tmp/testfile: failed to set up loop device: No such file or directory

Environment:

• kind version: (use kind version): v0.6.0-alpha