hst/fs: interface filesystem config

This allows mount points to be represented by different underlying structs.

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

hst/fsephemeral.go

@@ -0,0 +1,83 @@
+package hst
+
+import (
+	"encoding/gob"
+	"os"
+	"strings"
+
+	"hakurei.app/container"
+)
+
+func init() { gob.Register(new(FSEphemeral)) }
+
+// FilesystemEphemeral is the [FilesystemConfig.Type] name of a mount point with ephemeral state.
+const FilesystemEphemeral = "ephemeral"
+
+// FSEphemeral represents an ephemeral container mount point.
+type FSEphemeral struct {
+	// mount point in container
+	Dst *container.Absolute `json:"dst,omitempty"`
+	// do not mount filesystem read-only
+	Write bool `json:"write,omitempty"`
+	// upper limit on the size of the filesystem
+	Size int `json:"size,omitempty"`
+	// initial permission bits of the new filesystem
+	Perm os.FileMode `json:"perm,omitempty"`
+}
+
+func (e *FSEphemeral) Type() string { return FilesystemEphemeral }
+
+func (e *FSEphemeral) Target() *container.Absolute {
+	if e == nil {
+		return nil
+	}
+	return e.Dst
+}
+
+func (e *FSEphemeral) Host() []*container.Absolute { return nil }
+
+const fsEphemeralDefaultPerm = os.FileMode(0755)
+
+func (e *FSEphemeral) Apply(ops *container.Ops) {
+	if e == nil || e.Dst == nil {
+		return
+	}
+
+	size := e.Size
+	if size < 0 {
+		size = 0
+	}
+
+	perm := e.Perm
+	if perm == 0 {
+		perm = fsEphemeralDefaultPerm
+	}
+
+	if e.Write {
+		ops.Tmpfs(e.Dst, size, perm)
+	} else {
+		ops.Readonly(e.Dst, perm)
+	}
+}
+
+func (e *FSEphemeral) String() string {
+	if e == nil || e.Dst == nil {
+		return "<invalid>"
+	}
+
+	expr := new(strings.Builder)
+	expr.Grow(15 + len(FilesystemEphemeral) + len(e.Dst.String()))
+
+	if e.Write {
+		expr.WriteString("w")
+	}
+	expr.WriteString("+" + FilesystemEphemeral + "(")
+	if e.Perm != 0 {
+		expr.WriteString(e.Perm.String())
+	} else {
+		expr.WriteString(fsEphemeralDefaultPerm.String())
+	}
+	expr.WriteString("):" + e.Dst.String())
+
+	return expr.String()
+}