fusego/fuseutil/file_system.go

// 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 fuseutil

import (
	"flag"
	"io"
	"math/rand"
	"time"

	"github.com/jacobsa/fuse"
	"github.com/jacobsa/fuse/fuseops"
)

var fRandomDelays = flag.Bool(
	"fuseutil.random_delays", false,
	"If set, randomly delay each op received, to help expose concurrency issues.")

// An interface with a method for each op type in the fuseops package. This can
// be used in conjunction with NewFileSystemServer to avoid writing a "dispatch
// loop" that switches on op types, instead receiving typed method calls
// directly.
//
// Each method is responsible for calling Respond on the supplied op.
//
// See NotImplementedFileSystem for a convenient way to embed default
// implementations for methods you don't care about.
type FileSystem interface {
	Init(*fuseops.InitOp)
	LookUpInode(*fuseops.LookUpInodeOp)
	GetInodeAttributes(*fuseops.GetInodeAttributesOp)
	SetInodeAttributes(*fuseops.SetInodeAttributesOp)
	ForgetInode(*fuseops.ForgetInodeOp)
	MkDir(*fuseops.MkDirOp)
	CreateFile(*fuseops.CreateFileOp)
	CreateSymlink(*fuseops.CreateSymlinkOp)
	RmDir(*fuseops.RmDirOp)
	Unlink(*fuseops.UnlinkOp)
	OpenDir(*fuseops.OpenDirOp)
	ReadDir(*fuseops.ReadDirOp)
	ReleaseDirHandle(*fuseops.ReleaseDirHandleOp)
	OpenFile(*fuseops.OpenFileOp)
	ReadFile(*fuseops.ReadFileOp)
	WriteFile(*fuseops.WriteFileOp)
	SyncFile(*fuseops.SyncFileOp)
	FlushFile(*fuseops.FlushFileOp)
	ReleaseFileHandle(*fuseops.ReleaseFileHandleOp)
	ReadSymlink(*fuseops.ReadSymlinkOp)
}

// Create a fuse.Server that handles ops by calling the associated FileSystem
// method.Respond with the resulting error. Unsupported ops are responded to
// directly with ENOSYS.
//
// Each call to a FileSystem method is made on its own goroutine, and is free
// to block.
//
// (It is safe to naively process ops concurrently because the kernel
// guarantees to serialize operations that the user expects to happen in order,
// cf. http://goo.gl/jnkHPO, fuse-devel thread "Fuse guarantees on concurrent
// requests").
func NewFileSystemServer(fs FileSystem) fuse.Server {
	return fileSystemServer{fs}
}

// A convenience function that makes it easy to ensure you respond to an
// operation when a FileSystem method returns. Responds to op with the current
// value of *err.
//
// For example:
//
//     func (fs *myFS) ReadFile(op *fuseops.ReadFileOp) {
//       var err error
//       defer fuseutil.RespondToOp(op, &err)
//
//       if err = fs.frobnicate(); err != nil {
//         err = fmt.Errorf("frobnicate: %v", err)
//         return
//       }
//
//       // Lots more manipulation of err, and return paths.
//       // [...]
//     }
//
func RespondToOp(op fuseops.Op, err *error) {
	op.Respond(*err)
}

type fileSystemServer struct {
	fs FileSystem
}

func (s fileSystemServer) ServeOps(c *fuse.Connection) {
	for {
		op, err := c.ReadOp()
		if err == io.EOF {
			break
		}

		if err != nil {
			panic(err)
		}

		go s.handleOp(op)
	}
}

func (s fileSystemServer) handleOp(op fuseops.Op) {
	// Delay if requested.
	if *fRandomDelays {
		const delayLimit = 100 * time.Microsecond
		delay := time.Duration(rand.Int63n(int64(delayLimit)))
		time.Sleep(delay)
	}

	// Dispatch to the appropriate method.
	switch typed := op.(type) {
	default:
		op.Respond(fuse.ENOSYS)

	case *fuseops.InitOp:
		s.fs.Init(typed)

	case *fuseops.LookUpInodeOp:
		s.fs.LookUpInode(typed)

	case *fuseops.GetInodeAttributesOp:
		s.fs.GetInodeAttributes(typed)

	case *fuseops.SetInodeAttributesOp:
		s.fs.SetInodeAttributes(typed)

	case *fuseops.ForgetInodeOp:
		s.fs.ForgetInode(typed)

	case *fuseops.MkDirOp:
		s.fs.MkDir(typed)

	case *fuseops.CreateFileOp:
		s.fs.CreateFile(typed)

	case *fuseops.CreateSymlinkOp:
		s.fs.CreateSymlink(typed)

	case *fuseops.RmDirOp:
		s.fs.RmDir(typed)

	case *fuseops.UnlinkOp:
		s.fs.Unlink(typed)

	case *fuseops.OpenDirOp:
		s.fs.OpenDir(typed)

	case *fuseops.ReadDirOp:
		s.fs.ReadDir(typed)

	case *fuseops.ReleaseDirHandleOp:
		s.fs.ReleaseDirHandle(typed)

	case *fuseops.OpenFileOp:
		s.fs.OpenFile(typed)

	case *fuseops.ReadFileOp:
		s.fs.ReadFile(typed)

	case *fuseops.WriteFileOp:
		s.fs.WriteFile(typed)

	case *fuseops.SyncFileOp:
		s.fs.SyncFile(typed)

	case *fuseops.FlushFileOp:
		s.fs.FlushFile(typed)

	case *fuseops.ReleaseFileHandleOp:
		s.fs.ReleaseFileHandle(typed)

	case *fuseops.ReadSymlinkOp:
		s.fs.ReadSymlink(typed)
	}
}