For some reason, shared mount propagation between the host
and a container does not work for btrfs, unless container
root directory (i.e. graphdriver home) is a bind mount.
The above issue was reproduced on SLES 12sp3 + btrfs using
the following script:
#!/bin/bash
set -eux -o pipefail
# DIR should not be under a subvolume
DIR=${DIR:-/lib}
MNT=$DIR/my-mnt
FILE=$MNT/file
ID=$(docker run -d --privileged -v $DIR:$DIR:rshared ubuntu sleep 24h)
docker exec $ID mkdir -p $MNT
docker exec $ID mount -t tmpfs tmpfs $MNT
docker exec $ID touch $FILE
ls -l $FILE
umount $MNT
docker rm -f $ID
which fails this way:
+ ls -l /lib/my-mnt/file
ls: cannot access '/lib/my-mnt/file': No such file or directory
meaning the mount performed inside a priviledged container is not
propagated back to the host (even if all the mounts have "shared"
propagation mode).
The remedy to the above is to make graphdriver home a bind mount.
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
(cherry picked from commit 16d822bba8ac5ab22c8697750f700403bca3dbf3)
Upstream-commit: fa8ac946165b8004a15e85744e774ed6ba99fd38
Component: engine
d00ceca6f0