This commit is a set of fixes and improvement for zfs graph driver,
in particular:
1. Remove mount point after umount in `Get()` error path, as well
as in `Put()` (with `MNT_DETACH` flag). This should solve "failed
to remove root filesystem for <ID> .... dataset is busy" error
reported in Moby issue 35642.
To reproduce the issue:
- start dockerd with zfs
- docker run -d --name c1 --rm busybox top
- docker run -d --name c2 --rm busybox top
- docker stop c1
- docker rm c1
Output when the bug is present:
```
Error response from daemon: driver "zfs" failed to remove root
filesystem for XXX : exit status 1: "/sbin/zfs zfs destroy -r
scratch/docker/YYY" => cannot destroy 'scratch/docker/YYY':
dataset is busy
```
Output when the bug is fixed:
```
Error: No such container: c1
```
(as the container has been successfully autoremoved on stop)
2. Fix/improve error handling in `Get()` -- do not try to umount
if `refcount` > 0
3. Simplifies unmount in `Get()`. Specifically, remove call to
`graphdriver.Mounted()` (which checks if fs is mounted using
`statfs()` and check for fs type) and `mount.Unmount()` (which
parses `/proc/self/mountinfo`). Calling `unix.Unmount()` is
simple and sufficient.
4. Add unmounting of driver's home to `Cleanup()`.
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
Upstream-commit: a450a575a672b90f02a4b1d3d9300ce1d70a6311
Component: engine
f1cfd038e2