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// Copyright 2015 Google Inc. All Rights Reserved.
// 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,
// See the License for the specific language governing permissions and
// limitations under the License.
package fuse
import (
// A type that knows how to serve ops read from a connection.
type Server interface {
// Read and serve ops from the supplied connection until EOF. Do not return
// until all operations have been responded to. Must not be called more than
// once.
// A struct representing the status of a mount operation, with a method that
// waits for unmounting.
type MountedFileSystem struct {
dir string
// The result to return from Join. Not valid until the channel is closed.
joinStatus error
joinStatusAvailable chan struct{}
// Return the directory on which the file system is mounted (or where we
// attempted to mount it.)
func (mfs *MountedFileSystem) Dir() string {
return mfs.dir
// Block until a mounted file system has been unmounted. Do not return
// successfully until all ops read from the connection have been responded to
// (i.e. the file system server has finished processing all in-flight ops).
// The return value will be non-nil if anything unexpected happened while
// serving. May be called multiple times.
func (mfs *MountedFileSystem) Join(ctx context.Context) error {
select {
case <-mfs.joinStatusAvailable:
return mfs.joinStatus
case <-ctx.Done():
return ctx.Err()
// Optional configuration accepted by Mount.
type MountConfig struct {
// The context from which every op read from the connetion by the sever
// should inherit. If nil, context.Background() will be used.
OpContext context.Context
// If non-empty, the name of the file system as displayed by e.g. `mount`.
// This is important because the `umount` command requires root privileges if
// it doesn't agree with /etc/fstab.
FSName string
// Mount the file system in read-only mode. File modes will appear as normal,
// but opening a file for writing and metadata operations like chmod,
// chtimes, etc. will fail.
ReadOnly bool
// A logger to use for logging errors. All errors are logged, with the
// exception of a few blacklisted errors that are expected. If nil, no error
// logging is performed.
ErrorLogger *log.Logger
// A logger to use for logging debug information. If nil, no debug logging is
// performed.
DebugLogger *log.Logger
// OS X only.
// Normally on OS X we mount with the novncache option
// (cf. http://goo.gl/1pTjuk), which disables entry caching in the kernel.
// This is because osxfuse does not honor the entry expiration values we
// return to it, instead caching potentially forever (cf.
// http://goo.gl/8yR0Ie), and it is probably better to fail to cache than to
// cache for too long, since the latter is more likely to hide consistency
// bugs that are difficult to detect and diagnose.
// This field disables the use of novncache, restoring entry caching. Beware:
// the value of ChildInodeEntry.EntryExpiration is ignored by the kernel, and
// entries will be cached for an arbitrarily long time.
EnableVnodeCaching bool
// Additional key=value options to pass unadulterated to the underlying mount
// command. See `man 8 mount`, the fuse documentation, etc. for
// system-specific information.
// For expert use only! May invalidate other guarantees made in the
// documentation for this package.
Options map[string]string
// Convert to mount options to be passed to package fuseshim.
func (c *MountConfig) bazilfuseOptions() (opts []fuseshim.MountOption) {
isDarwin := runtime.GOOS == "darwin"
// Enable permissions checking in the kernel. See the comments on
// InodeAttributes.Mode.
opts = append(opts, fuseshim.SetOption("default_permissions", ""))
// HACK(jacobsa): Work around what appears to be a bug in systemd v219, as
// shipped in Ubuntu 15.04, where it automatically unmounts any file system
// that doesn't set an explicit name.
// When Ubuntu contains systemd v220, this workaround should be removed and
// the systemd bug reopened if the problem persists.
// Cf. https://github.com/bazil/fuse/issues/89
// Cf. https://bugs.freedesktop.org/show_bug.cgi?id=90907
fsname := c.FSName
if runtime.GOOS == "linux" && fsname == "" {
fsname = "some_fuse_file_system"
// Special file system name?
if fsname != "" {
opts = append(opts, fuseshim.FSName(fsname))
// Read only?
if c.ReadOnly {
opts = append(opts, fuseshim.ReadOnly())
// OS X: set novncache when appropriate.
if isDarwin && !c.EnableVnodeCaching {
opts = append(opts, fuseshim.SetOption("novncache", ""))
// OS X: disable the use of "Apple Double" (._foo and .DS_Store) files, which
// just add noise to debug output and can have significant cost on
// network-based file systems.
// Cf. https://github.com/osxfuse/osxfuse/wiki/Mount-options
if isDarwin {
opts = append(opts, fuseshim.SetOption("noappledouble", ""))
// Ask the Linux kernel for larger read requests.
// As of 2015-03-26, the behavior in the kernel is:
// * (http://goo.gl/bQ1f1i, http://goo.gl/HwBrR6) Set the local variable
// ra_pages to be init_response->max_readahead divided by the page size.
// * (http://goo.gl/gcIsSh, http://goo.gl/LKV2vA) Set
// backing_dev_info::ra_pages to the min of that value and what was sent
// in the request's max_readahead field.
// * (http://goo.gl/u2SqzH) Use backing_dev_info::ra_pages when deciding
// how much to read ahead.
// * (http://goo.gl/JnhbdL) Don't read ahead at all if that field is zero.
// Reading a page at a time is a drag. Ask for a larger size.
const maxReadahead = 1 << 20
opts = append(opts, fuseshim.MaxReadahead(maxReadahead))
// Last but not least: other user-supplied options.
for k, v := range c.Options {
opts = append(opts, fuseshim.SetOption(k, v))
// Attempt to mount a file system on the given directory, using the supplied
// Server to serve connection requests. This function blocks until the file
// system is successfully mounted.
func Mount(
dir string,
server Server,
config *MountConfig) (mfs *MountedFileSystem, err error) {
// Initialize the struct.
mfs = &MountedFileSystem{
dir: dir,
joinStatusAvailable: make(chan struct{}),
// Open a fuseshim connection.
bfConn, err := fuseshim.Mount(mfs.dir, config.bazilfuseOptions()...)
if err != nil {
err = fmt.Errorf("fuseshim.Mount: %v", err)
// Choose a parent context for ops.
opContext := config.OpContext
if opContext == nil {
opContext = context.Background()
// Create our own Connection object wrapping it.
connection, err := newConnection(
if err != nil {
err = fmt.Errorf("newConnection: %v", err)
// Serve the connection in the background. When done, set the join status.
go func() {
mfs.joinStatus = connection.close()
// Wait for the connection to say it is ready.
if err = connection.waitForReady(); err != nil {
err = fmt.Errorf("WaitForReady: %v", err)