syscall.go

//
// Copyright 2015 The rkt Authors
// Copyright (c) 2016 Intel Corporation
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//

package virtcontainers

import (
	"fmt"
	"os"
	"path/filepath"
	"syscall"
)

const mountPerm = os.FileMode(0755)

// bindMount bind mounts a source in to a destination. This will
// do some bookkeeping:
// * evaluate all symlinks
// * ensure the source exists
// * recursively create the destination
func bindMount(source, destination string, readonly bool) error {
	if source == "" {
		return fmt.Errorf("source must be specified")
	}
	if destination == "" {
		return fmt.Errorf("destination must be specified")
	}

	absSource, err := filepath.EvalSymlinks(source)
	if err != nil {
		return fmt.Errorf("Could not resolve symlink for source %v", source)
	}

	if err := ensureDestinationExists(absSource, destination); err != nil {
		return fmt.Errorf("Could not create destination mount point %v: %v", destination, err)
	} else if err := syscall.Mount(absSource, destination, "bind", syscall.MS_BIND, ""); err != nil {
		return fmt.Errorf("Could not bind mount %v to %v: %v", absSource, destination, err)
	}

	// For readonly bind mounts, we need to remount with the readonly flag.
	// This is needed as only very recent versions of libmount/util-linux support "bind,ro"
	if readonly {
		return syscall.Mount(absSource, destination, "bind", uintptr(syscall.MS_BIND|syscall.MS_REMOUNT|syscall.MS_RDONLY), "")
	}

	return nil
}

// ensureDestinationExists will recursively create a given mountpoint. If directories
// are created, their permissions are initialized to mountPerm
func ensureDestinationExists(source, destination string) error {
	fileInfo, err := os.Stat(source)
	if err != nil {
		return fmt.Errorf("could not stat source location %v: %v", source, err)
	}

	targetPathParent, _ := filepath.Split(destination)
	if err := os.MkdirAll(targetPathParent, mountPerm); err != nil {
		return fmt.Errorf("could not create parent directory %v: %v", targetPathParent, err)
	}

	if fileInfo.IsDir() {
		if err := os.Mkdir(destination, mountPerm); !os.IsExist(err) {
			return err
		}
	} else {
		file, err := os.OpenFile(destination, os.O_CREATE, mountPerm)
		if err != nil {
			return err
		}

		file.Close()
	}
	return nil
}