From 8e08e8f51882fd8152eec349117f4f8dd7e056f0 Mon Sep 17 00:00:00 2001
From: Ophestra <cat@gensokyo.uk>
Date: Wed, 7 Jan 2026 03:14:33 +0900
Subject: internal/pkg: automatic overlay mount on work

This directly submits the upperdir to cache. It is primarily used in bootstrapping where tools are limited and should not be used unless there is a very good reason to.

Signed-off-by: Ophestra <cat@gensokyo.uk>
---
 internal/pkg/exec.go | 50 +++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 39 insertions(+), 11 deletions(-)

(limited to 'internal/pkg/exec.go')

diff --git a/internal/pkg/exec.go b/internal/pkg/exec.go
index 6e050b15..8d736b5b 100644
--- a/internal/pkg/exec.go
+++ b/internal/pkg/exec.go
@@ -16,6 +16,9 @@ import (
 	"hakurei.app/message"
 )
 
+// AbsWork is the container pathname [CureContext.GetWorkDir] is mounted on.
+var AbsWork = fhs.AbsRoot.Append("work/")
+
 // ExecContainerPath is an [Artifact] and the [check.Absolute] pathname to make
 // it available under in the container.
 type ExecContainerPath struct {
@@ -90,9 +93,14 @@ func (a *execNetArtifact) Cure(c *CureContext) error {
 // A private instance of /proc and /dev is made available to the container.
 //
 // The working and temporary directories are both created and mounted writable
-// on /work and /tmp respectively. If one or more paths target [fhs.AbsTmp], the
-// final entry is set up as a writable overlay mount on /tmp backed by the host
-// side temporary directory.
+// on [AbsWork] and [fhs.AbsTmp] respectively. If one or more paths target
+// [fhs.AbsTmp], the final entry is set up as a writable overlay mount on /tmp
+// backed by the host side temporary directory. If one or more paths target
+// [AbsWork], the final entry is set up as a writable overlay mount on /work for
+// which the upperdir is the host side work directory. In this configuration,
+// the program must avoid causing whiteout files to be created, cure fails if
+// upperdir ends up with anything other than directory, regular or symlink
+// entries.
 //
 // If the first path targets [fhs.AbsRoot], it is made writable via an overlay
 // mount with writes going to an ephemeral tmpfs bound to the lifetime of the
@@ -186,7 +194,7 @@ func (a *execArtifact) cure(c *CureContext, hostNet bool) (err error) {
 		cures = runtime.NumCPU()
 	}
 
-	overlayTempIndex := -1
+	overlayTempIndex, overlayWorkIndex := -1, -1
 	paths := make([][2]*check.Absolute, len(a.paths))
 	for i, p := range a.paths {
 		if p.P == nil || p.A == nil {
@@ -194,6 +202,8 @@ func (a *execArtifact) cure(c *CureContext, hostNet bool) (err error) {
 		}
 		if p.P.Is(fhs.AbsTmp) {
 			overlayTempIndex = i
+		} else if p.P.Is(AbsWork) {
+			overlayWorkIndex = i
 		}
 		paths[i][1] = p.P
 	}
@@ -280,11 +290,12 @@ func (a *execArtifact) cure(c *CureContext, hostNet bool) (err error) {
 		z.OverlayEphemeral(fhs.AbsRoot, paths[0][0])
 		paths = paths[1:]
 		overlayTempIndex--
+		overlayWorkIndex--
 	}
 
+	temp, work := c.GetTempDir(), c.GetWorkDir()
 	for i, b := range paths {
 		if i == overlayTempIndex {
-			temp := c.GetTempDir()
 			tempUpper := temp.Append("upper")
 			if err = os.MkdirAll(tempUpper.String(), 0700); err != nil {
 				return
@@ -301,14 +312,31 @@ func (a *execArtifact) cure(c *CureContext, hostNet bool) (err error) {
 			)
 			continue
 		}
+		if i == overlayWorkIndex {
+			if err = os.MkdirAll(work.String(), 0700); err != nil {
+				return
+			}
+			tempWork := temp.Append(".work")
+			if err = os.MkdirAll(tempWork.String(), 0700); err != nil {
+				return
+			}
+			z.Overlay(
+				AbsWork,
+				work,
+				tempWork,
+				b[0],
+			)
+			continue
+		}
 		z.Bind(b[0], b[1], 0)
 	}
-	work := c.GetWorkDir()
-	z.Bind(
-		work,
-		fhs.AbsRoot.Append("work"),
-		std.BindWritable|std.BindEnsure,
-	)
+	if overlayWorkIndex < 0 {
+		z.Bind(
+			work,
+			AbsWork,
+			std.BindWritable|std.BindEnsure,
+		)
+	}
 	if overlayTempIndex < 0 {
 		z.Bind(
 			c.GetTempDir(),
-- 
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