container/init: split setup ops into individual files

This significantly increases readability.

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

container/initbind.go

@@ -0,0 +1,95 @@
+package container
+
+import (
+	"encoding/gob"
+	"fmt"
+	"os"
+	"path/filepath"
+	. "syscall"
+)
+
+func init() { gob.Register(new(BindMountOp)) }
+
+// Bind appends an [Op] that bind mounts host path [BindMountOp.Source] on container path [BindMountOp.Target].
+func (f *Ops) Bind(source, target *Absolute, flags int) *Ops {
+	*f = append(*f, &BindMountOp{nil, source, target, flags})
+	return f
+}
+
+// BindMountOp bind mounts host path Source on container path Target.
+// Note that Flags uses bits declared in this package and should not be set with constants in [syscall].
+type BindMountOp struct {
+	sourceFinal, Source, Target *Absolute
+
+	Flags int
+}
+
+const (
+	// BindOptional skips nonexistent host paths.
+	BindOptional = 1 << iota
+	// BindWritable mounts filesystem read-write.
+	BindWritable
+	// BindDevice allows access to devices (special files) on this filesystem.
+	BindDevice
+)
+
+func (b *BindMountOp) early(*setupState) error {
+	if b.Source == nil || b.Target == nil {
+		return EBADE
+	}
+
+	if pathname, err := filepath.EvalSymlinks(b.Source.String()); err != nil {
+		if os.IsNotExist(err) && b.Flags&BindOptional != 0 {
+			// leave sourceFinal as nil
+			return nil
+		}
+		return wrapErrSelf(err)
+	} else {
+		b.sourceFinal, err = NewAbs(pathname)
+		return err
+	}
+}
+
+func (b *BindMountOp) apply(*setupState) error {
+	if b.sourceFinal == nil {
+		if b.Flags&BindOptional == 0 {
+			// unreachable
+			return EBADE
+		}
+		return nil
+	}
+
+	source := toHost(b.sourceFinal.String())
+	target := toSysroot(b.Target.String())
+
+	// this perm value emulates bwrap behaviour as it clears bits from 0755 based on
+	// op->perms which is never set for any bind setup op so always results in 0700
+	if fi, err := os.Stat(source); err != nil {
+		return wrapErrSelf(err)
+	} else if fi.IsDir() {
+		if err = os.MkdirAll(target, 0700); err != nil {
+			return wrapErrSelf(err)
+		}
+	} else if err = ensureFile(target, 0444, 0700); err != nil {
+		return err
+	}
+
+	var flags uintptr = MS_REC
+	if b.Flags&BindWritable == 0 {
+		flags |= MS_RDONLY
+	}
+	if b.Flags&BindDevice == 0 {
+		flags |= MS_NODEV
+	}
+
+	return hostProc.bindMount(source, target, flags, b.sourceFinal == b.Target)
+}
+
+func (b *BindMountOp) Is(op Op) bool { vb, ok := op.(*BindMountOp); return ok && *b == *vb }
+func (*BindMountOp) prefix() string  { return "mounting" }
+func (b *BindMountOp) String() string {
+	if b.Source == b.Target {
+		return fmt.Sprintf("%q flags %#x", b.Source, b.Flags)
+	}
+	return fmt.Sprintf("%q on %q flags %#x", b.Source, b.Target, b.Flags)
+}