cmd/app: alternative merged template layout

This implements an optional, alternative template layout to accommodate
ZFS and equivalent setups where each template occupies a different
filesystem. In such a setup, the default, separate workdir is unusable
as overlayfs requires the workdir to reside on the same filesystem as
the writable upperdir. The "merge" build tag enables this alternative
behaviour.

Signed-off-by: Ophestra <cat@gensokyo.uk>

1 files changed, 18 insertions, 17 deletions

diff --git a/cmd/app/main.go b/cmd/app/main.go
index 5f796cfc..9b51d601 100644
--- a/cmd/app/main.go
+++ b/cmd/app/main.go
@@ -37,7 +37,7 @@ func main() {
 		flagBase     string
 		flagInsecure bool
 
-		base, template, initial *check.Absolute
+		b *base
 	)
 	c := command.New(os.Stderr, log.Printf, "app", func([]string) (err error) {
 		msg.SwapVerbose(flagVerbose)
@@ -45,14 +45,15 @@ func main() {
 		if flagBase == "" {
 			flagBase = "state"
 		}
+
+		var a *check.Absolute
 		if flagBase, err = filepath.Abs(flagBase); err != nil {
 			return
-		} else if base, err = check.NewAbs(flagBase); err != nil {
+		} else if a, err = check.NewAbs(flagBase); err != nil {
 			return
 		}
+		b = (*base)(a)
 
-		template = base.Append("template")
-		initial = base.Append("initial")
 		return
 	}).Flag(
 		&flagVerbose,
@@ -77,7 +78,7 @@ func main() {
 			"enter", "Enter mutable state template",
 			func(args []string) error {
 				if len(args) != 1 {
-					return list(template, true)
+					return list(b.append("template"), true)
 				}
 
 				config := hst.Config{
@@ -87,9 +88,9 @@ func main() {
 						Filesystem: []hst.FilesystemConfigJSON{
 							{FilesystemConfig: &hst.FSOverlay{
 								Target: fhs.AbsRoot,
-								Lower:  []*check.Absolute{initial},
-								Upper:  template.Append(args[0]),
-								Work:   base.Append("work", args[0]),
+								Lower:  []*check.Absolute{b.initial()},
+								Upper:  b.template(args[0]),
+								Work:   b.work(args[0]),
 							}},
 							{FilesystemConfig: &hst.FSEphemeral{
 								Target: fhs.AbsTmp,
@@ -123,7 +124,7 @@ func main() {
 					config.Container.Home = a
 				}
 
-				remove, err := acquireTemplate(base, args[0])
+				remove, err := acquireTemplate(b, args[0])
 				if err != nil {
 					return err
 				}
@@ -149,19 +150,19 @@ func main() {
 			"run", "Start the named application",
 			func(args []string) error {
 				if len(args) < 1 {
-					return list(base.Append("app"), false)
+					return list(b.append("app"), false)
 				}
 
 				var config *hst.Config
 				var r io.Reader
-				f, err := os.Open(base.Append("app", args[0]).String())
+				f, err := os.Open(b.append("app", args[0]).String())
 				if err != nil {
 					return err
 				}
 				r = f
 
 				var common *os.File
-				if common, err = os.Open(base.Append("common").String()); err != nil {
+				if common, err = os.Open(b.append("common").String()); err != nil {
 					if !errors.Is(err, os.ErrNotExist) {
 						_ = f.Close()
 						return err
@@ -171,7 +172,7 @@ func main() {
 				}
 
 				var name string
-				config, err = parse(args[0], base, r, &name)
+				config, err = parse(args[0], b, r, &name)
 				if closeErr := f.Close(); err == nil {
 					err = closeErr
 				}
@@ -188,7 +189,7 @@ func main() {
 					config.Container.Args[2] = flagCommand
 				}
 
-				if err = enterTemplate(base, name); err != nil {
+				if err = enterTemplate(b, name); err != nil {
 					return err
 				}
 				return run(ctx, msg, flagInsecure, config, args[1:]...)
@@ -231,7 +232,7 @@ func main() {
 		"next", "Find next unused identity",
 		func([]string) error {
 			var names []string
-			if dents, err := os.ReadDir(base.Append("app").String()); err != nil {
+			if dents, err := os.ReadDir(b.append("app").String()); err != nil {
 				return err
 			} else {
 				names = make([]string, 0, len(dents))
@@ -246,12 +247,12 @@ func main() {
 
 			apps := make([]*hst.Config, len(names))
 			for i, name := range names {
-				r, err := os.Open(base.Append("app", name).String())
+				r, err := os.Open(b.append("app", name).String())
 				if err != nil {
 					return err
 				}
 
-				apps[i], err = parse(name, base, r, nil)
+				apps[i], err = parse(name, b, r, nil)
 				if closeErr := r.Close(); err == nil {
 					err = closeErr
 				}