providers/system: support .d directory for base config fragments

Fixes #1101
This change was inspired by coreos/fedora-coreos-config#626, which allows
the two distros to carry different base.ign files with common elements. Also,
this will support an additional .d directory for each platform ID.

dracut/30ignition/ignition-setup-base.sh

@@ -5,15 +5,15 @@ copy_file_if_exists() {
     src="${1}"; dst="${2}"
     if [ -f "${src}" ]; then
         echo "Copying ${src} to ${dst}"
-        cp "${src}" "${dst}"
+        cp -r "${src}" "${dst}"
     else
         echo "File ${src} does not exist.. Skipping copy"
     fi
 }
 
-destination=/usr/lib/ignition
+destination=/usr/lib/ignition/base.${PLATFORM_ID}.d
 mkdir -p $destination
 
-# We will support grabbing a platform specific base.ign config
-# from the initrd at /usr/lib/ignition/platform/${PLATFORM_ID}/base.ign
-copy_file_if_exists "/usr/lib/ignition/platform/${PLATFORM_ID}/base.ign" "${destination}/base.ign"
+# We will support grabbing platform-specific config fragments
+# from the initrd at /usr/lib/ignition/platform/${PLATFORM_ID}/
+copy_file_if_exists "/usr/lib/ignition/platform/${PLATFORM_ID}/" "${destination}/"

internal/providers/system/system.go

@@ -15,10 +15,13 @@
 package system
 
 import (
+	"fmt"
 	"io/ioutil"
 	"os"
 	"path/filepath"
+	"strings"
 
+	latest "github.com/coreos/ignition/v2/config/v3_2_experimental"
 	"github.com/coreos/ignition/v2/config/v3_2_experimental/types"
 	"github.com/coreos/ignition/v2/internal/distro"
 	"github.com/coreos/ignition/v2/internal/log"
@@ -30,12 +33,26 @@ import (
 )
 
 const (
-	baseFilename = "base.ign"
 	userFilename = "user.ign"
 )
 
 func FetchBaseConfig(logger *log.Logger) (types.Config, report.Report, error) {
-	return fetchConfig(logger, baseFilename)
+	baseDirectory := "base.d"
+	// Assuming we get only single directory which is either
+	// a `base.d` or a `base.${PLATFORM_ID}.d`.
+	contents, err := ioutil.ReadDir(distro.SystemConfigDir())
+	if err != nil {
+		return types.Config{}, report.Report{}, err
+	}
+	for _, content := range contents {
+		if content.IsDir() {
+			if strings.Contains(content.Name(), "base") && len(strings.Split(content.Name(), ".")) == 3 {
+				baseDirectory = content.Name()
+			}
+		}
+	}
+	path := filepath.Join(distro.SystemConfigDir(), baseDirectory)
+	return fetchBaseConfig(logger, path)
 }
 
 func FetchConfig(f *resource.Fetcher) (types.Config, report.Report, error) {
@@ -56,3 +73,24 @@ func fetchConfig(logger *log.Logger, filename string) (types.Config, report.Repo
 	}
 	return util.ParseConfig(logger, rawConfig)
 }
+
+func fetchBaseConfig(logger *log.Logger, path string) (types.Config, report.Report, error) {
+	var baseConfig, fullSystemBaseConfig types.Config
+	configs, err := ioutil.ReadDir(path)
+	if os.IsNotExist(err) {
+		logger.Info("no config dir at %q", path)
+		return types.Config{}, report.Report{}, err
+	} else if err != nil {
+		logger.Err("couldn't read config dir %q: %v", path, err)
+		return types.Config{}, report.Report{}, err
+	}
+	for _, config := range configs {
+		file := fmt.Sprintf("%s/%s", path, config.Name())
+		systemBaseConfig, _, err := fetchConfig(logger, file)
+		if err != nil {
+			return types.Config{}, report.Report{}, err
+		}
+		fullSystemBaseConfig = latest.Merge(baseConfig, systemBaseConfig)
+	}
+	return fullSystemBaseConfig, report.Report{}, nil
+}