syscallcompat: retry ops on EINTR

Retry operations that have been shown to throw EINTR
errors on CIFS.

Todo: Solution for this pain in the back:

	warning: unix.Getdents returned errno 2 in the middle of data
	rm: cannot remove 'linux-3.0.old3/Documentation/ABI/removed': Input/output error

Progress towards fixing https://github.com/rfjakob/gocryptfs/issues/483 .

internal/fusefrontend/file.go

@@ -409,7 +409,7 @@ func (f *File) Flush(ctx context.Context) syscall.Errno {
 	if err != nil {
 		return fs.ToErrno(err)
 	}
-	err = syscall.Close(newFd)
+	err = syscallcompat.Close(newFd)
 	return fs.ToErrno(err)
 }
 

internal/fusefrontend/node_dir_ops.go

@@ -306,7 +306,7 @@ retry:
 		return fs.ToErrno(err)
 	}
 	if err != nil {
-		tlog.Warn.Printf("Rmdir: Readdirnames: %v", err)
+		tlog.Warn.Printf("Rmdir: Getdents: %v", err)
 		return fs.ToErrno(err)
 	}
 	// MacOS sprinkles .DS_Store files everywhere. This is hard to avoid for

internal/fusefrontend/root_node.go

@@ -203,6 +203,8 @@ func (rn *RootNode) openWriteOnlyFile(dirfd int, cName string, newFlags int) (rw
 //
 // openBackingDir is secure against symlink races by using Openat and
 // ReadDirIVAt.
+//
+// Retries on EINTR.
 func (rn *RootNode) openBackingDir(relPath string) (dirfd int, cName string, err error) {
 	dirRelPath := nametransform.Dir(relPath)
 	// With PlaintextNames, we don't need to read DirIVs. Easy.
@@ -216,7 +218,7 @@ func (rn *RootNode) openBackingDir(relPath string) (dirfd int, cName string, err
 		return dirfd, cName, nil
 	}
 	// Open cipherdir (following symlinks)
-	dirfd, err = syscall.Open(rn.args.Cipherdir, syscall.O_DIRECTORY|syscallcompat.O_PATH, 0)
+	dirfd, err = syscallcompat.Open(rn.args.Cipherdir, syscall.O_DIRECTORY|syscallcompat.O_PATH, 0)
 	if err != nil {
 		return -1, "", err
 	}

internal/nametransform/diriv.go

@@ -23,6 +23,7 @@ const (
 
 // ReadDirIVAt reads "gocryptfs.diriv" from the directory that is opened as "dirfd".
 // Using the dirfd makes it immune to concurrent renames of the directory.
+// Retries on EINTR.
 func ReadDirIVAt(dirfd int) (iv []byte, err error) {
 	fdRaw, err := syscallcompat.Openat(dirfd, DirIVFilename,
 		syscall.O_RDONLY|syscall.O_NOFOLLOW, 0)

internal/syscallcompat/eintr.go

@@ -0,0 +1,48 @@
+package syscallcompat
+
+import (
+	"syscall"
+)
+
+// retryEINTR executes operation `op` and retries if it gets EINTR.
+//
+// Like ignoringEINTR() in the Go stdlib:
+// https://github.com/golang/go/blob/d2a80f3fb5b44450e0b304ac5a718f99c053d82a/src/os/file_posix.go#L243
+//
+// This is needed because CIFS throws lots of EINTR errors:
+// https://github.com/rfjakob/gocryptfs/issues/483
+func retryEINTR(op func() error) error {
+	for {
+		err := op()
+		if err != syscall.EINTR {
+			return err
+		}
+	}
+}
+
+// retryEINTR2 is like retryEINTR but for functions that return an (int, error)
+// pair like syscall.Create().
+func retryEINTR2(op func() (int, error)) (int, error) {
+	for {
+		ret, err := op()
+		if err != syscall.EINTR {
+			return ret, err
+		}
+	}
+}
+
+// Open wraps syscall.Open.
+// Retries on EINTR.
+func Open(path string, mode int, perm uint32) (fd int, err error) {
+	fd, err = retryEINTR2(func() (int, error) {
+		return syscall.Open(path, mode, perm)
+	})
+	return fd, err
+}
+
+// Close wraps syscall.Close.
+// Retries on EINTR.
+func Close(fd int) (err error) {
+	err = retryEINTR(func() error { return syscall.Close(fd) })
+	return err
+}

internal/syscallcompat/open_nofollow.go

@@ -13,6 +13,7 @@ import (
 // This function is implemented by walking the directory tree, starting at
 // "baseDir", using the Openat syscall with the O_NOFOLLOW flag.
 // Symlinks that are part of the "baseDir" path are followed.
+// Retries on EINTR.
 func OpenDirNofollow(baseDir string, relPath string) (fd int, err error) {
 	if !filepath.IsAbs(baseDir) {
 		tlog.Warn.Printf("BUG: OpenDirNofollow called with relative baseDir=%q", baseDir)
@@ -23,7 +24,9 @@ func OpenDirNofollow(baseDir string, relPath string) (fd int, err error) {
 		return -1, syscall.EINVAL
 	}
 	// Open the base dir (following symlinks)
-	dirfd, err := syscall.Open(baseDir, syscall.O_DIRECTORY|O_PATH, 0)
+	dirfd, err := retryEINTR2(func() (int, error) {
+		return syscall.Open(baseDir, syscall.O_DIRECTORY|O_PATH, 0)
+	})
 	if err != nil {
 		return -1, err
 	}

internal/syscallcompat/sys_common.go

@@ -44,7 +44,8 @@ func Faccessat(dirfd int, path string, mode uint32) error {
 	return unix.Faccessat(dirfd, path, mode, 0)
 }
 
-// Openat wraps the Openat syscall, retrying on EINTR.
+// Openat wraps the Openat syscall.
+// Retries on EINTR.
 func Openat(dirfd int, path string, flags int, mode uint32) (fd int, err error) {
 	if flags&syscall.O_CREAT != 0 {
 		// O_CREAT should be used with O_EXCL. O_NOFOLLOW has no effect with O_EXCL.
@@ -59,24 +60,28 @@ func Openat(dirfd int, path string, flags int, mode uint32) (fd int, err error)
 			flags |= syscall.O_NOFOLLOW
 		}
 	}
-	// Like ignoringEINTR() in the Go stdlib:
-	// https://github.com/golang/go/blob/d2a80f3fb5b44450e0b304ac5a718f99c053d82a/src/os/file_posix.go#L243
-	for {
-		fd, err = unix.Openat(dirfd, path, flags, mode)
-		if err != unix.EINTR {
-			return fd, err
-		}
-	}
+	fd, err = retryEINTR2(func() (int, error) {
+		return unix.Openat(dirfd, path, flags, mode)
+	})
+	return fd, err
 }
 
 // Renameat wraps the Renameat syscall.
+// Retries on EINTR.
 func Renameat(olddirfd int, oldpath string, newdirfd int, newpath string) (err error) {
-	return unix.Renameat(olddirfd, oldpath, newdirfd, newpath)
+	err = retryEINTR(func() error {
+		return unix.Renameat(olddirfd, oldpath, newdirfd, newpath)
+	})
+	return err
 }
 
 // Unlinkat syscall.
+// Retries on EINTR.
 func Unlinkat(dirfd int, path string, flags int) (err error) {
-	return unix.Unlinkat(dirfd, path, flags)
+	err = retryEINTR(func() error {
+		return unix.Unlinkat(dirfd, path, flags)
+	})
+	return err
 }
 
 // Fchownat syscall.
@@ -105,17 +110,22 @@ func Mkdirat(dirfd int, path string, mode uint32) (err error) {
 }
 
 // Fstatat syscall.
+// Retries on EINTR.
 func Fstatat(dirfd int, path string, stat *unix.Stat_t, flags int) (err error) {
 	// Why would we ever want to call this without AT_SYMLINK_NOFOLLOW?
 	if flags&unix.AT_SYMLINK_NOFOLLOW == 0 {
 		tlog.Warn.Printf("Fstatat: adding missing AT_SYMLINK_NOFOLLOW flag")
 		flags |= unix.AT_SYMLINK_NOFOLLOW
 	}
-	return unix.Fstatat(dirfd, path, stat, flags)
+	err = retryEINTR(func() error {
+		return unix.Fstatat(dirfd, path, stat, flags)
+	})
+	return err
 }
 
 // Fstatat2 is a more convenient version of Fstatat. It allocates a Stat_t
 // for you and also handles the Unix2syscall conversion.
+// Retries on EINTR.
 func Fstatat2(dirfd int, path string, flags int) (*syscall.Stat_t, error) {
 	var stUnix unix.Stat_t
 	err := Fstatat(dirfd, path, &stUnix, flags)

internal/syscallcompat/sys_linux.go

@@ -265,9 +265,13 @@ func FutimesNano(fd int, a *time.Time, m *time.Time) (err error) {
 }
 
 // UtimesNanoAtNofollow is like UtimesNanoAt but never follows symlinks.
+// Retries on EINTR.
 func UtimesNanoAtNofollow(dirfd int, path string, a *time.Time, m *time.Time) (err error) {
 	ts := timesToTimespec(a, m)
-	return unix.UtimesNanoAt(dirfd, path, ts, unix.AT_SYMLINK_NOFOLLOW)
+	err = retryEINTR(func() error {
+		return unix.UtimesNanoAt(dirfd, path, ts, unix.AT_SYMLINK_NOFOLLOW)
+	})
+	return err
 }
 
 // Getdents syscall.
@@ -276,6 +280,10 @@ func Getdents(fd int) ([]fuse.DirEntry, error) {
 }
 
 // Renameat2 does not exist on Darwin, so we have to wrap it here.
+// Retries on EINTR.
 func Renameat2(olddirfd int, oldpath string, newdirfd int, newpath string, flags uint) (err error) {
-	return unix.Renameat2(olddirfd, oldpath, newdirfd, newpath, flags)
+	err = retryEINTR(func() error {
+		return unix.Renameat2(olddirfd, oldpath, newdirfd, newpath, flags)
+	})
+	return err
 }