feat(vfscore): Introduce vfscore automount parameterization

In preparation for individual volume auto-mounting to Unikraft[0],
introduce a helper library to serialize command-line arguments
representing the in-kernel mount path for a device and its options.

[0]: unikraft/unikraft#979

Signed-off-by: Alexander Jung <alex@unikraft.io>

unikraft/export/v0/vfscore/library.go

@@ -0,0 +1,7 @@
+// SPDX-License-Identifier: BSD-3-Clause
+// Copyright (c) 2022, Unikraft GmbH and The KraftKit Authors.
+// Licensed under the BSD-3-Clause License (the "License").
+// You may not use this file except in compliance with the License.
+package vfscore
+
+const LibraryName = "vfscore"

unikraft/export/v0/vfscore/params.go

@@ -0,0 +1,50 @@
+// SPDX-License-Identifier: BSD-3-Clause
+// Copyright (c) 2022, Unikraft GmbH and The KraftKit Authors.
+// Licensed under the BSD-3-Clause License (the "License").
+// You may not use this file except in compliance with the License.
+package vfscore
+
+import (
+	"strings"
+
+	"kraftkit.sh/unikraft/export/v0/ukargparse"
+)
+
+var ParamVfsAutomount = ukargparse.NewParamStrSlice("vfs", "automount", nil)
+
+// ExportedParams returns the parameters available by this exported library.
+func ExportedParams() []ukargparse.Param {
+	return []ukargparse.Param{
+		ParamVfsAutomount,
+	}
+}
+
+// Automount is a vfscore mount entry.
+type Automount struct {
+	sourceDevice string
+	mountTarget  string
+	fsDriver     string
+	options      string
+}
+
+// NewAutomount generates a structure that is representative of one of
+// Unikraft's vfscore automounts.
+func NewAutomount(sourceDevice, mountTarget, fsDriver, options string) Automount {
+	return Automount{
+		sourceDevice,
+		mountTarget,
+		fsDriver,
+		options,
+	}
+}
+
+// String implements fmt.Stringer and returns a valid vfs.automount-formatted
+// entry.
+func (automount Automount) String() string {
+	return strings.Join([]string{
+		automount.sourceDevice,
+		automount.mountTarget,
+		automount.fsDriver,
+		automount.options,
+	}, ":")
+}