it traverses and watch plugin directory and its sub directory recursively,
plugin socket file only need be unique within one directory,
- plugin socket directory
- |
- ---->sub directory 1
- | |
- | -----> socket1, socket2 ...
- ----->sub directory 2
- |
- ------> socket1, socket2 ...
the design itself allow sub directory be anything,
but in practical, each plugin type could just use one sub directory.
four bonus changes added as below
1. extract example handler out from test, it is easier to read the code
with the seperation.
2. there are two variables here: "Watcher" and "watcher".
"Watcher" is the plugin watcher, and "watcher" is the fsnotify watcher.
so rename the "watcher" to "fsWatcher" to make code easier to
understand.
3. change RegisterCallbackFn() return value order, it is
conventional to return error last, after this change,
the pkg/volume/csi is compliance with golint, so remove it
from hack/.golint_failures
4. refactor errors handling at invokeRegistrationCallbackAtHandler()
to make error message more clear.
Automatic merge from submit-queue (batch tested with PRs 64416, 63625, 60967, 64767, 64588). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.
Remove mount.GetMountRefs in favor of mounter.GetMountRefs
**What this PR does / why we need it**:
Currently, there are two `GetMountRefs` functions:
- `mount.GetMountRefs`: used in various volume plugins
- `<mounter>.GetMountRefs` (previously `mount.GetMountRefsByDev` introduced in [#49988](https://github.com/kubernetes/kubernetes/pull/49988/files#diff-0c0020e71c995790a90ad9c61ede7632R154), moved to `Mounter` interface in #62903)
This is confusing, and it's better to implement `GetMountRefs` on mounter interface, because different mounters can have their own implementation (especially for nsenter).
This pr removes `mount.GetMountRefs` in favor of mounter.GetMountRefs.
More discussions: https://github.com/kubernetes/kubernetes/pull/62102#issuecomment-390081884 and https://github.com/kubernetes/kubernetes/pull/62102#issuecomment-390123022.
**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixes #
**Special notes for your reviewer**:
**Release note**:
```release-note
NONE
```
