Implements fallback if rootfs image not found

config/config.go

@@ -150,6 +150,12 @@ func (dt DistroType) MarshalTOML() (data []byte, err error) {
 	return
 }
 
+type ByRootFS []KernelInfo
+
+func (a ByRootFS) Len() int           { return len(a) }
+func (a ByRootFS) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
+func (a ByRootFS) Less(i, j int) bool { return a[i].RootFS < a[j].RootFS }
+
 type KernelInfo struct {
 	DistroType    DistroType
 	DistroRelease string // 18.04/7.4.1708/9.1

main.go

@@ -9,12 +9,46 @@ import (
 	"os"
 	"os/exec"
 	"os/user"
+	"sort"
 
 	kingpin "gopkg.in/alecthomas/kingpin.v2"
 
 	"github.com/jollheef/out-of-tree/config"
 )
 
+func findFallback(kcfg config.KernelConfig, ki config.KernelInfo) (rootfs string) {
+	for _, k := range kcfg.Kernels {
+		if !exists(k.RootFS) || k.DistroType != ki.DistroType {
+			continue
+		}
+		if k.RootFS < ki.RootFS {
+			rootfs = k.RootFS
+			return
+		}
+	}
+	return
+}
+
+func handleFallbacks(kcfg config.KernelConfig) {
+	sort.Sort(sort.Reverse(config.ByRootFS(kcfg.Kernels)))
+
+	for i, k := range kcfg.Kernels {
+		if !exists(k.RootFS) {
+			newRootFS := findFallback(kcfg, k)
+
+			s := k.RootFS + " does not exists "
+			if newRootFS != "" {
+				s += "(fallback to " + newRootFS + ")"
+			} else {
+				s += "(no fallback found)"
+			}
+
+			kcfg.Kernels[i].RootFS = newRootFS
+			log.Println(s)
+		}
+	}
+}
+
 func main() {
 	app := kingpin.New(
 		"out-of-tree",
@@ -109,6 +143,8 @@ func main() {
 		}
 	}
 
+	handleFallbacks(kcfg)
+
 	switch kingpin.MustParse(app.Parse(os.Args[1:])) {
 	case pewCommand.FullCommand():
 		err = pewHandler(kcfg, *path, *pewKernel, *pewBinary,