A Go package for implementing a FUSE file system (fork with 'almost' zero-copy read/write)
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fusego/mount.go

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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,
// 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 fuse
import (
"context"
"fmt"
"log"
"net"
"os"
"os/exec"
"strings"
"syscall"
)
// Server is an interface for any 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.
ServeOps(*Connection)
}
// Mount attempts to mount a file system on the given directory, using the
// supplied Server to serve connection requests. It blocks until the file
// system is successfully mounted.
func Mount(
dir string,
server Server,
config *MountConfig) (*MountedFileSystem, error) {
// Sanity check: make sure the mount point exists and is a directory. This
// saves us from some confusing errors later on OS X.
if err := checkMountPoint(dir); err != nil {
return nil, err
}
// Initialize the struct.
mfs := &MountedFileSystem{
dir: dir,
joinStatusAvailable: make(chan struct{}),
}
// Begin the mounting process, which will continue in the background.
if config.DebugLogger != nil {
config.DebugLogger.Println("Beginning the mounting kickoff process")
}
ready := make(chan error, 1)
dev, err := mount(dir, config, ready)
if err != nil {
return nil, fmt.Errorf("mount: %v", err)
}
if config.DebugLogger != nil {
config.DebugLogger.Println("Completed the mounting kickoff process")
}
// Choose a parent context for ops.
cfgCopy := *config
if cfgCopy.OpContext == nil {
cfgCopy.OpContext = context.Background()
}
if config.DebugLogger != nil {
config.DebugLogger.Println("Creating a connection object")
}
// Create a Connection object wrapping the device.
connection, err := newConnection(
cfgCopy,
config.DebugLogger,
config.ErrorLogger,
dev)
if err != nil {
return nil, fmt.Errorf("newConnection: %v", err)
}
if config.DebugLogger != nil {
config.DebugLogger.Println("Successfully created the connection")
}
// Serve the connection in the background. When done, set the join status.
go func() {
server.ServeOps(connection)
mfs.joinStatus = connection.close()
close(mfs.joinStatusAvailable)
}()
if config.DebugLogger != nil {
config.DebugLogger.Println("Waiting for mounting process to complete")
}
// Wait for the mount process to complete.
if err := <-ready; err != nil {
return nil, fmt.Errorf("mount (background): %v", err)
}
return mfs, nil
}
func checkMountPoint(dir string) error {
if strings.HasPrefix(dir, "/dev/fd") {
return nil
}
fi, err := os.Stat(dir)
switch {
case os.IsNotExist(err):
return err
case err != nil:
return fmt.Errorf("Statting mount point: %v", err)
case !fi.IsDir():
return fmt.Errorf("Mount point %s is not a directory", dir)
}
return nil
}
func fusermount(binary string, argv []string, additionalEnv []string, wait bool, debugLogger *log.Logger) (*os.File, error) {
if debugLogger != nil {
debugLogger.Println("Creating a socket pair")
}
// Create a socket pair.
fds, err := syscall.Socketpair(syscall.AF_UNIX, syscall.SOCK_STREAM, 0)
if err != nil {
return nil, fmt.Errorf("Socketpair: %v", err)
}
if debugLogger != nil {
debugLogger.Println("Creating files to wrap the sockets")
}
// Wrap the sockets into os.File objects that we will pass off to fusermount.
writeFile := os.NewFile(uintptr(fds[0]), "fusermount-child-writes")
defer writeFile.Close()
readFile := os.NewFile(uintptr(fds[1]), "fusermount-parent-reads")
defer readFile.Close()
if debugLogger != nil {
debugLogger.Println("Starting fusermount/os mount")
}
// Start fusermount/mount_macfuse/mount_osxfuse.
cmd := exec.Command(binary, argv...)
cmd.Env = append(os.Environ(), "_FUSE_COMMFD=3")
cmd.Env = append(cmd.Env, additionalEnv...)
cmd.ExtraFiles = []*os.File{writeFile}
cmd.Stderr = os.Stderr
// Run the command.
if wait {
err = cmd.Run()
} else {
err = cmd.Start()
}
if err != nil {
return nil, fmt.Errorf("running %v: %v", binary, err)
}
if debugLogger != nil {
debugLogger.Println("Wrapping socket pair in a connection")
}
// Wrap the socket file in a connection.
c, err := net.FileConn(readFile)
if err != nil {
return nil, fmt.Errorf("FileConn: %v", err)
}
defer c.Close()
if debugLogger != nil {
debugLogger.Println("Checking that we have a unix domain socket")
}
// We expect to have a Unix domain socket.
uc, ok := c.(*net.UnixConn)
if !ok {
return nil, fmt.Errorf("Expected UnixConn, got %T", c)
}
if debugLogger != nil {
debugLogger.Println("Read a message from socket")
}
// Read a message.
buf := make([]byte, 32) // expect 1 byte
oob := make([]byte, 32) // expect 24 bytes
_, oobn, _, _, err := uc.ReadMsgUnix(buf, oob)
if err != nil {
return nil, fmt.Errorf("ReadMsgUnix: %v", err)
}
// Parse the message.
scms, err := syscall.ParseSocketControlMessage(oob[:oobn])
if err != nil {
return nil, fmt.Errorf("ParseSocketControlMessage: %v", err)
}
// We expect one message.
if len(scms) != 1 {
return nil, fmt.Errorf("expected 1 SocketControlMessage; got scms = %#v", scms)
}
scm := scms[0]
if debugLogger != nil {
debugLogger.Println("Successfully read the socket message.")
}
// Pull out the FD returned by fusermount
gotFds, err := syscall.ParseUnixRights(&scm)
if err != nil {
return nil, fmt.Errorf("syscall.ParseUnixRights: %v", err)
}
if len(gotFds) != 1 {
return nil, fmt.Errorf("wanted 1 fd; got %#v", gotFds)
}
if debugLogger != nil {
debugLogger.Println("Converting FD into os.File")
}
// Turn the FD into an os.File.
return os.NewFile(uintptr(gotFds[0]), "/dev/fuse"), nil
}