syscallcompat: OSX: add Renamat wrapper

Adds a poor man's renameat implementation for OSX.

internal/fusefrontend/fs.go

@@ -4,6 +4,7 @@ package fusefrontend
 
 import (
 	"encoding/base64"
+	"fmt"
 	"os"
 	"path/filepath"
 	"sync"
@@ -17,6 +18,7 @@ import (
 	"github.com/rfjakob/gocryptfs/internal/contentenc"
 	"github.com/rfjakob/gocryptfs/internal/cryptocore"
 	"github.com/rfjakob/gocryptfs/internal/nametransform"
+	"github.com/rfjakob/gocryptfs/internal/syscallcompat"
 	"github.com/rfjakob/gocryptfs/internal/tlog"
 )
 
@@ -385,6 +387,7 @@ func (fs *FS) Rename(oldPath string, newPath string, context *fuse.Context) (cod
 		}
 		defer oldDirFd.Close()
 		finalOldDirFd = int(oldDirFd.Fd())
+		// Use relative path
 		finalOldPath = cOldName
 	}
 	// Handle long destination file name
@@ -399,6 +402,7 @@ func (fs *FS) Rename(oldPath string, newPath string, context *fuse.Context) (cod
 		}
 		defer newDirFd.Close()
 		finalNewDirFd = int(newDirFd.Fd())
+		// Use relative path
 		finalNewPath = cNewName
 		// Create destination .name file
 		err = fs.nameTransform.WriteLongName(newDirFd, cNewName, newPath)
@@ -407,7 +411,8 @@ func (fs *FS) Rename(oldPath string, newPath string, context *fuse.Context) (cod
 		}
 	}
 	// Actual rename
-	err = syscall.Renameat(finalOldDirFd, finalOldPath, finalNewDirFd, finalNewPath)
+	fmt.Printf("Renameat oldfd=%d oldpath=%s newfd=%d newpath=%s\n", finalOldDirFd, finalOldPath, finalNewDirFd, finalNewPath)
+	err = syscallcompat.Renameat(finalOldDirFd, finalOldPath, finalNewDirFd, finalNewPath)
 	if err == syscall.ENOTEMPTY || err == syscall.EEXIST {
 		// If an empty directory is overwritten we will always get an error as
 		// the "empty" directory will still contain gocryptfs.diriv.
@@ -416,7 +421,7 @@ func (fs *FS) Rename(oldPath string, newPath string, context *fuse.Context) (cod
 		// again.
 		tlog.Debug.Printf("Rename: Handling ENOTEMPTY")
 		if fs.Rmdir(newPath, context) == fuse.OK {
-			err = syscall.Renameat(finalOldDirFd, finalOldPath, finalNewDirFd, finalNewPath)
+			err = syscallcompat.Renameat(finalOldDirFd, finalOldPath, finalNewDirFd, finalNewPath)
 		}
 	}
 	if err != nil {

internal/fusefrontend/fs_dir.go

@@ -14,6 +14,7 @@ import (
 	"github.com/rfjakob/gocryptfs/internal/configfile"
 	"github.com/rfjakob/gocryptfs/internal/cryptocore"
 	"github.com/rfjakob/gocryptfs/internal/nametransform"
+	"github.com/rfjakob/gocryptfs/internal/syscallcompat"
 	"github.com/rfjakob/gocryptfs/internal/tlog"
 )
 
@@ -168,7 +169,7 @@ func (fs *FS) Rmdir(path string, context *fuse.Context) (code fuse.Status) {
 		// Protect against concurrent readers.
 		fs.dirIVLock.Lock()
 		defer fs.dirIVLock.Unlock()
-		err = syscall.Renameat(int(dirfd.Fd()), nametransform.DirIVFilename,
+		err = syscallcompat.Renameat(int(dirfd.Fd()), nametransform.DirIVFilename,
 			int(parentDirFd.Fd()), tmpName)
 		if err != nil {
 			tlog.Warn.Printf("Rmdir: Renaming %s to %s failed: %v",
@@ -182,7 +183,7 @@ func (fs *FS) Rmdir(path string, context *fuse.Context) (code fuse.Status) {
 		if err != nil {
 			// This can happen if another file in the directory was created in the
 			// meantime, undo the rename
-			err2 := syscall.Renameat(int(parentDirFd.Fd()), tmpName,
+			err2 := syscallcompat.Renameat(int(parentDirFd.Fd()), tmpName,
 				int(dirfd.Fd()), nametransform.DirIVFilename)
 			if err != nil {
 				tlog.Warn.Printf("Rmdir: Rename rollback failed: %v", err2)

internal/syscallcompat/sys_darwin.go

@@ -2,44 +2,87 @@ package syscallcompat
 
 import (
 	"os"
+	"path/filepath"
 	"sync"
 	"syscall"
 )
 
-// prealloc - preallocate space without changing the file size. This prevents
-// us from running out of space in the middle of an operation.
-func Prealloc(fd int, off int64, len int64) (err error) {
-	//
-	// Sorry, fallocate is not available on OSX at all and
-	// fcntl F_PREALLOCATE is not accessible from Go.
-	//
-	// See https://github.com/rfjakob/gocryptfs/issues/18 if you want to help.
+// Sorry, fallocate is not available on OSX at all and
+// fcntl F_PREALLOCATE is not accessible from Go.
+// See https://github.com/rfjakob/gocryptfs/issues/18 if you want to help.
+func EnospcPrealloc(fd int, off int64, len int64) (err error) {
 	return nil
 }
 
-var openatLock sync.Mutex
-
-// Poor man's Openat:
-// 1) fchdir to the dirfd
-// 2) open the file
-// 3) chdir back.
-func Openat(dirfd int, path string, flags int, mode uint32) (fd int, err error) {
-	openatLock.Lock()
-	defer openatLock.Unlock()
-
-	oldWd, err := os.Getwd()
-	if err != nil {
-		return -1, err
-	}
-	err = syscall.Fchdir(dirfd)
-	if err != nil {
-		return -1, err
-	}
-	defer os.Chdir(oldWd)
-
-	return syscall.Open(path, flags, mode)
-}
-
+// See above.
 func Fallocate(fd int, mode uint32, off int64, len int64) (err error) {
 	return syscall.EOPNOTSUPP
 }
+
+var chdirMutex sync.Mutex
+
+// Poor man's Openat
+func Openat(dirfd int, path string, flags int, mode uint32) (fd int, err error) {
+	chdirMutex.Lock()
+	defer chdirMutex.Unlock()
+	if !filepath.IsAbs(path) {
+		// Save the old working directory
+		oldWd, err := os.Getwd()
+		if err != nil {
+			return -1, err
+		}
+		// Chdir to target directory
+		err = syscall.Fchdir(dirfd)
+		if err != nil {
+			return -1, err
+		}
+		// Chdir back at the end
+		defer os.Chdir(oldWd)
+	}
+	return syscall.Open(path, flags, mode)
+}
+
+// Poor man's Renameat
+func Renameat(olddirfd int, oldpath string, newdirfd int, newpath string) (err error) {
+	chdirMutex.Lock()
+	defer chdirMutex.Unlock()
+	// Unless both paths are absolute we have to save the old working dir and
+	// Chdir(oldWd) back to it in the end. If we error out before the first
+	// chdir, Chdir(oldWd) is unneccassary but does no harm.
+	if !filepath.IsAbs(oldpath) || !filepath.IsAbs(newpath) {
+		oldWd, err := os.Getwd()
+		if err != nil {
+			return err
+		}
+		defer os.Chdir(oldWd)
+	}
+	// Make oldpath absolute
+	oldpath, err = dirfdAbs(olddirfd, oldpath)
+	if err != nil {
+		return err
+	}
+	// Make newpath absolute
+	newpath, err = dirfdAbs(newdirfd, newpath)
+	if err != nil {
+		return err
+	}
+	return syscall.Rename(oldpath, newpath)
+}
+
+// dirfdAbs transforms the dirfd-relative "path" to an absolute one. If the
+// path is not already absolute, this function will change the working
+// directory. The caller has to chdir back.
+func dirfdAbs(dirfd int, path string) (absPath string, err error) {
+	if filepath.IsAbs(path) {
+		return path, nil
+	}
+	err = syscall.Fchdir(dirfd)
+	if err != nil {
+		return "", err
+	}
+	wd, err := os.Getwd()
+	if err != nil {
+		return "", err
+	}
+	return filepath.Join(wd, path), nil
+}

internal/syscallcompat/sys_linux.go

@@ -37,10 +37,14 @@ func EnospcPrealloc(fd int, off int64, len int64) (err error) {
 	}
 }
 
+func Fallocate(fd int, mode uint32, off int64, len int64) (err error) {
+	return syscall.Fallocate(fd, mode, off, len)
+}
+
 func Openat(dirfd int, path string, flags int, mode uint32) (fd int, err error) {
 	return syscall.Openat(dirfd, path, flags, mode)
 }
 
-func Fallocate(fd int, mode uint32, off int64, len int64) (err error) {
-	return syscall.Fallocate(fd, mode, off, len)
+func Renameat(olddirfd int, oldpath string, newdirfd int, newpath string) (err error) {
+	return syscall.Renameat(olddirfd, oldpath, newdirfd, newpath)
 }