internal/pkg: automatic overlay mount on tmp

This sets up the last Artifact to target /tmp as a writable overlay mount backed by the host side temp directory. This is useful for an Artifact containing source code to be built for another Artifact for example.

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

internal/pkg/dir_test.go

@@ -380,6 +380,36 @@ func TestFlatten(t *testing.T) {
 			{Mode: fs.ModeDir | 0700, Path: "temp"},
 			{Mode: fs.ModeDir | 0700, Path: "work"},
 		}, pkg.MustDecode("gFT9kprYBqEJKifJIl2sHn_3TgULWVLTU4DrYAHiGcRmcdFRZ0YtjiROW820cAEc")},
+
+		{"sample exec container overlay temp", fstest.MapFS{
+			".": {Mode: fs.ModeDir | 0700},
+
+			"checksum": {Mode: fs.ModeDir | 0700},
+			"checksum/GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9":       {Mode: fs.ModeDir | 0500},
+			"checksum/GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9/check": {Mode: 0400, Data: []byte{0}},
+			"checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU":       {Mode: fs.ModeDir | 0500},
+
+			"identifier": {Mode: fs.ModeDir | 0700},
+			"identifier/3ELJ8l42g6XeIoLGR9LheVhMIwSIleD6VrhsliBuon5DAdBOwFSMqd7aiUI4fll7": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9")},
+			"identifier/nfeISfLeFDr1k-g3hpE1oZ440kTqDdfF8TDpoLdbTPqaMMIl95oiqcvqjRkMjubA": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU")},
+
+			"temp": {Mode: fs.ModeDir | 0700},
+			"work": {Mode: fs.ModeDir | 0700},
+		}, []pkg.FlatEntry{
+			{Mode: fs.ModeDir | 0700, Path: "."},
+
+			{Mode: fs.ModeDir | 0700, Path: "checksum"},
+			{Mode: fs.ModeDir | 0500, Path: "checksum/GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9"},
+			{Mode: 0400, Path: "checksum/GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9/check", Data: []byte{0}},
+			{Mode: fs.ModeDir | 0500, Path: "checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU"},
+
+			{Mode: fs.ModeDir | 0700, Path: "identifier"},
+			{Mode: fs.ModeSymlink | 0777, Path: "identifier/3ELJ8l42g6XeIoLGR9LheVhMIwSIleD6VrhsliBuon5DAdBOwFSMqd7aiUI4fll7", Data: []byte("../checksum/GPa4aBakdSJd7Tz7LYj_VJFoojzyZinmVcG3k6M5xI6CZ821J5sXLhLDDuS47gi9")},
+			{Mode: fs.ModeSymlink | 0777, Path: "identifier/nfeISfLeFDr1k-g3hpE1oZ440kTqDdfF8TDpoLdbTPqaMMIl95oiqcvqjRkMjubA", Data: []byte("../checksum/MGWmEfjut2QE2xPJwTsmUzpff4BN_FEnQ7T0j7gvUCCiugJQNwqt9m151fm9D1yU")},
+
+			{Mode: fs.ModeDir | 0700, Path: "temp"},
+			{Mode: fs.ModeDir | 0700, Path: "work"},
+		}, pkg.MustDecode("_r1IBeMWCkLwQ9Im9w0tV9_CWIOfQlXkkP2CogPHLmZp_AB6W3_8HVZqDV00dNAm")},
 	}
 	for _, tc := range testCases {
 		t.Run(tc.name, func(t *testing.T) {

internal/pkg/exec.go

@@ -89,7 +89,9 @@ 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.
+// 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.
 //
 // 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
@@ -273,18 +275,46 @@ func (a *execArtifact) cure(c *CureContext, hostNet bool) (err error) {
 		z.OverlayEphemeral(fhs.AbsRoot, paths[0][0])
 		paths = paths[1:]
 	}
+	var overlayTemp *check.Absolute
 	for _, b := range paths {
+		if b[1].Is(fhs.AbsTmp) {
+			if overlayTemp != nil {
+				z.Bind(overlayTemp, fhs.AbsTmp, 0)
+			}
+			overlayTemp = b[0]
+			continue
+		}
 		z.Bind(b[0], b[1], 0)
 	}
 	z.Bind(
 		c.GetWorkDir(),
 		fhs.AbsRoot.Append("work"),
 		std.BindWritable|std.BindEnsure,
-	).Bind(
-		c.GetTempDir(),
-		fhs.AbsTmp,
-		std.BindWritable|std.BindEnsure,
-	).Proc(fhs.AbsProc).Dev(fhs.AbsDev, true)
+	)
+	if overlayTemp == nil {
+		z.Bind(
+			c.GetTempDir(),
+			fhs.AbsTmp,
+			std.BindWritable|std.BindEnsure,
+		)
+	} else {
+		temp := c.GetTempDir()
+		tempUpper := temp.Append("upper")
+		if err = os.MkdirAll(tempUpper.String(), 0700); err != nil {
+			return
+		}
+		tempWork := temp.Append("work")
+		if err = os.MkdirAll(tempWork.String(), 0700); err != nil {
+			return
+		}
+		z.Overlay(
+			fhs.AbsTmp,
+			tempUpper,
+			tempWork,
+			overlayTemp,
+		)
+	}
+	z.Proc(fhs.AbsProc).Dev(fhs.AbsDev, true)
 
 	if err = z.Start(); err != nil {
 		return

internal/pkg/exec_test.go

@@ -11,6 +11,7 @@ import (
 	"testing"
 
 	"hakurei.app/container/check"
+	"hakurei.app/container/fhs"
 	"hakurei.app/container/stub"
 	"hakurei.app/hst"
 	"hakurei.app/internal/pkg"
@@ -189,6 +190,48 @@ func TestExec(t *testing.T) {
 
 			testtoolDestroy(t, base, c)
 		}, pkg.MustDecode("gFT9kprYBqEJKifJIl2sHn_3TgULWVLTU4DrYAHiGcRmcdFRZ0YtjiROW820cAEc")},
+
+		{"overlay temp", nil, func(t *testing.T, base *check.Absolute, c *pkg.Cache) {
+			c.SetStrict(true)
+			testtool, testtoolDestroy := newTesttool()
+
+			msg := message.New(log.New(os.Stderr, "container: ", 0))
+			msg.SwapVerbose(testing.Verbose())
+
+			cureMany(t, c, []cureStep{
+				{"container", pkg.NewExec(
+					t.Context(),
+					msg,
+					0,
+					nil,
+					check.MustAbs("/work"),
+					[]string{"HAKUREI_TEST=1", "HAKUREI_ROOT=1"},
+					check.MustAbs("/tmp/bin/testtool"),
+					[]string{"testtool"},
+
+					pkg.MustPath("/", stubArtifact{
+						kind:   pkg.KindTar,
+						params: []byte("empty directory"),
+						cure: func(c *pkg.CureContext) error {
+							return os.MkdirAll(c.GetWorkDir().String(), 0700)
+						},
+					}),
+					pkg.MustPath("/tmp/", stubArtifact{
+						kind:   pkg.KindTar,
+						params: []byte("empty directory"),
+						cure: func(c *pkg.CureContext) error {
+							return os.MkdirAll(c.GetWorkDir().String(), 0700)
+						},
+					}),
+					pkg.ExecContainerPath{
+						P: fhs.AbsTmp,
+						A: testtool,
+					},
+				), ignorePathname, wantChecksumOffline, nil},
+			})
+
+			testtoolDestroy(t, base, c)
+		}, pkg.MustDecode("_r1IBeMWCkLwQ9Im9w0tV9_CWIOfQlXkkP2CogPHLmZp_AB6W3_8HVZqDV00dNAm")},
 	})
 }
 

internal/pkg/testdata/main.go

@@ -39,11 +39,19 @@ func main() {
 	if !slices.Equal(wantEnv, os.Environ()) {
 		log.Fatalf("Environ: %q, want %q", os.Environ(), wantEnv)
 	}
-	const wantExec = "/opt/bin/testtool"
+
+	var overlayTmp bool
+	const (
+		wantExec        = "/opt/bin/testtool"
+		wantExecOverlay = "/tmp/bin/testtool"
+	)
 	if got, err := os.Executable(); err != nil {
 		log.Fatalf("Executable: error = %v", err)
 	} else if got != wantExec {
-		log.Fatalf("Executable: %q, want %q", got, wantExec)
+		if got != wantExecOverlay {
+			log.Fatalf("Executable: %q, want %q", got, wantExec)
+		}
+		overlayTmp = true
 	}
 
 	wantHostname := "cure"
@@ -105,7 +113,6 @@ func main() {
 		if path.Base(lowerdir) != checksumEmptyDir {
 			log.Fatal("unexpected artifact checksum")
 		}
-
 	} else {
 		if hostNet {
 			ident = "I3T53NtN6HPAyyodHtq2B0clcsoS1nPdvCEb-Zc5K-hoqFGL2od1mftHhwG7gX1S"
@@ -126,7 +133,16 @@ func main() {
 		}
 	}
 
-	next() // testtool artifact
+	if !overlayTmp {
+		next() // testtool artifact
+	} else {
+		ident = "3ELJ8l42g6XeIoLGR9LheVhMIwSIleD6VrhsliBuon5DAdBOwFSMqd7aiUI4fll7"
+
+		next()
+		if path.Base(m.Root) != checksumEmptyDir || m.Target != "/tmp" {
+			log.Fatal("unexpected artifact checksum")
+		}
+	}
 
 	next()
 	if path.Base(m.Root) != ident || m.Target != "/work" {
@@ -134,8 +150,16 @@ func main() {
 	}
 
 	next()
-	if path.Base(m.Root) != ident || m.Target != "/tmp" {
-		log.Fatal("unexpected temp mount entry")
+	if !overlayTmp {
+		if path.Base(m.Root) != ident || m.Target != "/tmp" {
+			log.Fatal("unexpected temp mount entry")
+		}
+	} else {
+		// testtool artifact
+		if m.Root != "/" || m.Target != "/tmp" ||
+			m.Source != "overlay" || m.FsType != "overlay" {
+			log.Fatal("unexpected temp mount entry")
+		}
 	}
 
 	next()