Allow split configurations by default: import conf/*.toml by default.

Distro vendor might want to customize their containerd configuration
and might prefer to split it in multiple files. Usually this is done
with a /etc/tool.d/*.conf scheme (for example /etc/sysctl.d). This would
allow distro to put any toml file in /etc/containerd/conf in Linux to
customize the default configuration.

Signed-off-by: Romain Geissler <romain.geissler@amadeus.com>

cmd/containerd/command/config.go

@@ -166,6 +166,7 @@ func platformAgnosticDefaultConfig() *srvconfig.Config {
 		},
 		DisabledPlugins:  []string{},
 		RequiredPlugins:  []string{},
+		Imports:          defaults.DefaultImports,
 		StreamProcessors: streamProcessors(),
 	}
 }

defaults/defaults.go

@@ -30,3 +30,8 @@ const (
 	// default snapshotter
 	DefaultSnapshotterNSLabel = "containerd.io/defaults/snapshotter"
 )
+
+var (
+	// DefaultImports is the default imports for config files.
+	DefaultImports = []string{"conf/*.toml"}
+)

docs/man/containerd-config.toml.5.md

@@ -143,7 +143,7 @@ documentation.
   "io.containerd.timeout.shim.shutdown" = "3s"
   "io.containerd.timeout.task.state" = "2s" -->
 
-**imports**
+**imports** (Default: ["conf/*.toml"])
 : Imports is a list of additional configuration files to include.
 This allows to split the main configuration file and keep some sections
 separately (for example vendors may keep a custom runtime configuration in a