container/initoverlay: configure via fsconfig

This works around the page size limit at the cost of negligible performance regressions.

Closes #34.

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

container/initoverlay.go

@@ -4,9 +4,9 @@ import (
 	"encoding/gob"
 	"fmt"
 	"slices"
-	"strings"
 
 	"hakurei.app/check"
+	"hakurei.app/ext"
 	"hakurei.app/fhs"
 )
 
@@ -150,7 +150,7 @@ func (o *MountOverlayOp) early(_ *setupState, k syscallDispatcher) error {
 			if v, err := k.evalSymlinks(o.Upper.String()); err != nil {
 				return err
 			} else {
-				o.upper = check.EscapeOverlayDataSegment(toHost(v))
+				o.upper = toHost(v)
 			}
 		}
 
@@ -158,7 +158,7 @@ func (o *MountOverlayOp) early(_ *setupState, k syscallDispatcher) error {
 			if v, err := k.evalSymlinks(o.Work.String()); err != nil {
 				return err
 			} else {
-				o.work = check.EscapeOverlayDataSegment(toHost(v))
+				o.work = toHost(v)
 			}
 		}
 	}
@@ -168,12 +168,39 @@ func (o *MountOverlayOp) early(_ *setupState, k syscallDispatcher) error {
 		if v, err := k.evalSymlinks(a.String()); err != nil {
 			return err
 		} else {
-			o.lower[i] = check.EscapeOverlayDataSegment(toHost(v))
+			o.lower[i] = toHost(v)
 		}
 	}
 	return nil
 }
 
+// mountOverlay sets up an overlay mount via [ext.FS].
+func mountOverlay(target string, options [][2]string) error {
+	fs, err := ext.OpenFS(SourceOverlay, 0)
+	if err != nil {
+		return err
+	}
+	if err = fs.SetString("source", SourceOverlay); err != nil {
+		_ = fs.Close()
+		return err
+	}
+	for _, option := range options {
+		if err = fs.SetString(option[0], option[1]); err != nil {
+			_ = fs.Close()
+			return err
+		}
+	}
+	if err = fs.SetFlag(OptionOverlayUserxattr); err != nil {
+		_ = fs.Close()
+		return err
+	}
+	if err = fs.Mount(target, 0); err != nil {
+		_ = fs.Close()
+		return err
+	}
+	return fs.Close()
+}
+
 func (o *MountOverlayOp) apply(state *setupState, k syscallDispatcher) error {
 	target := o.Target.String()
 	if !o.noPrefix {
@@ -194,7 +221,7 @@ func (o *MountOverlayOp) apply(state *setupState, k syscallDispatcher) error {
 		}
 	}
 
-	options := make([]string, 0, 4)
+	options := make([][2]string, 0, 2+len(o.lower))
 
 	if o.upper == zeroString && o.work == zeroString { // readonly
 		if len(o.Lower) < 2 {
@@ -205,15 +232,16 @@ func (o *MountOverlayOp) apply(state *setupState, k syscallDispatcher) error {
 		if len(o.Lower) == 0 {
 			return &OverlayArgumentError{OverlayEmptyLower, zeroString}
 		}
-		options = append(options,
-			OptionOverlayUpperdir+"="+o.upper,
-			OptionOverlayWorkdir+"="+o.work)
+		options = append(options, [][2]string{
+			{OptionOverlayUpperdir, o.upper},
+			{OptionOverlayWorkdir, o.work},
+		}...)
+	}
+	for _, lower := range o.lower {
+		options = append(options, [2]string{OptionOverlayLowerdir + "+", lower})
 	}
-	options = append(options,
-		OptionOverlayLowerdir+"="+strings.Join(o.lower, check.SpecialOverlayPath),
-		OptionOverlayUserxattr)
 
-	return k.mount(SourceOverlay, target, FstypeOverlay, 0, strings.Join(options, check.SpecialOverlayOption))
+	return k.mountOverlay(target, options)
 }
 
 func (o *MountOverlayOp) late(*setupState, syscallDispatcher) error { return nil }