Since these are registered and the interface is what matters, these
Service types do not need to be exported.
Signed-off-by: Michael Crosby <crosbymichael@gmail.com>
With this change, we integrate all the plugin changes into the
introspection service.
All plugins can be listed with the following command:
```console
$ ctr plugins
TYPE ID PLATFORM STATUS
io.containerd.content.v1 content - ok
io.containerd.metadata.v1 bolt - ok
io.containerd.differ.v1 walking linux/amd64 ok
io.containerd.grpc.v1 containers - ok
io.containerd.grpc.v1 content - ok
io.containerd.grpc.v1 diff - ok
io.containerd.grpc.v1 events - ok
io.containerd.grpc.v1 healthcheck - ok
io.containerd.grpc.v1 images - ok
io.containerd.grpc.v1 namespaces - ok
io.containerd.snapshotter.v1 btrfs linux/amd64 error
io.containerd.snapshotter.v1 overlayfs linux/amd64 ok
io.containerd.grpc.v1 snapshots - ok
io.containerd.monitor.v1 cgroups linux/amd64 ok
io.containerd.runtime.v1 linux linux/amd64 ok
io.containerd.grpc.v1 tasks - ok
io.containerd.grpc.v1 version - ok
```
There are few things to note about this output. The first is that it is
printed in the order in which plugins are initialized. This useful for
debugging plugin initialization problems. Also note that even though the
introspection GPRC api is a itself a plugin, it is not listed. This is
because the plugin takes a snapshot of the initialization state at the
end of the plugin init process. This allows us to see errors from each
plugin, as they happen. If it is required to introspect the existence of
the introspection service, we can make modifications to include it in
the future.
The last thing to note is that the btrfs plugin is in an error state.
This is a common state for containerd because even though we load the
plugin, most installations aren't on top of btrfs and the plugin cannot
be used. We can actually view this error using the detailed view with a
filter:
```console
$ ctr plugins --detailed id==btrfs
Type: io.containerd.snapshotter.v1
ID: btrfs
Platforms: linux/amd64
Exports:
root /var/lib/containerd/io.containerd.snapshotter.v1.btrfs
Error:
Code: Unknown
Message: path /var/lib/containerd/io.containerd.snapshotter.v1.btrfs must be a btrfs filesystem to be used with the btrfs snapshotter
```
Along with several other values, this is a valuable tool for evaluating the
state of components in containerd.
Signed-off-by: Stephen J Day <stephen.day@docker.com>
