containerd · fidencio · May 9, 2024 · AkihiroSuda · Jul 20, 2025 · fidencio
diff --git a/plugins/snapshots/blockfile/blockfile.go b/plugins/snapshots/blockfile/blockfile.go
@@ -19,16 +19,13 @@ package blockfile
 import (
 	"context"
 	"fmt"
-	"io"
 	"os"
 	"path/filepath"
-	"runtime"
 	"slices"
 
 	"github.com/containerd/containerd/v2/core/mount"
 	"github.com/containerd/containerd/v2/core/snapshots"
 	"github.com/containerd/containerd/v2/core/snapshots/storage"
-	"github.com/containerd/continuity/fs"
 	"github.com/containerd/log"
 	"github.com/containerd/plugin"
 )
@@ -452,31 +449,3 @@ func (o *snapshotter) mounts(s storage.Snapshot) []mount.Mount {
 func (o *snapshotter) Close() error {
 	return o.ms.Close()
 }
-
-func copyFileWithSync(target, source string) error {
-	// The Go stdlib does not seem to have an efficient os.File.ReadFrom
-	// routine for other platforms like it does on Linux with
-	// copy_file_range. For Darwin at least we can use clonefile
-	// in its place, otherwise if we have a sparse file we'd have
-	// a fun surprise waiting below.
-	//
-	// TODO: Enlighten other platforms (windows?)
-	if runtime.GOOS == "darwin" {
-		return fs.CopyFile(target, source)
-	}
-
-	src, err := os.Open(source)
-	if err != nil {
-		return fmt.Errorf("failed to open source %s: %w", source, err)
-	}
-	defer src.Close()
-	tgt, err := os.Create(target)
-	if err != nil {
-		return fmt.Errorf("failed to open target %s: %w", target, err)
-	}
-	defer tgt.Close()
-	defer tgt.Sync()
-
-	_, err = io.Copy(tgt, src)
-	return err
-}
diff --git a/plugins/snapshots/blockfile/blockfile_darwin.go b/plugins/snapshots/blockfile/blockfile_darwin.go
@@ -0,0 +1,27 @@
+/*
+   Copyright The containerd Authors.
+
+   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 blockfile
+
+import "github.com/containerd/continuity/fs"
+
+func copyFileWithSync(target, source string) error {
+	// The Go stdlib does not seem to have an efficient os.File.ReadFrom
+	// routine for other platforms like it does on Linux with
+	// copy_file_range. For Darwin at least we can use clonefile
+	// in its place.
+	return fs.CopyFile(target, source)
+}
diff --git a/plugins/snapshots/blockfile/blockfile_default.go b/plugins/snapshots/blockfile/blockfile_default.go
@@ -0,0 +1,46 @@
+//go:build !linux && !darwin
+
+/*
+   Copyright The containerd Authors.
+
+   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 blockfile
+
+import (
+	"fmt"
+	"io"
+	"os"
+)
+
+func copyFileWithSync(target, source string) error {
+	src, err := os.Open(source)
+	if err != nil {
+		return fmt.Errorf("failed to open source %s: %w", source, err)
+	}
+	defer src.Close()
+	tgt, err := os.Create(target)
+	if err != nil {
+		return fmt.Errorf("failed to open target %s: %w", target, err)
+	}
+	defer tgt.Close()
+	defer tgt.Sync()
+
+	_, err = io.Copy(tgt, src)
+	if err != nil {
+		return fmt.Errorf("failed to copy file to target %s: %w", target, err)
+	}
+
+	return err
+}
diff --git a/plugins/snapshots/blockfile/blockfile_linux.go b/plugins/snapshots/blockfile/blockfile_linux.go
@@ -0,0 +1,114 @@
+/*
+   Copyright The containerd Authors.
+
+   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 blockfile
+
+import (
+	"fmt"
+	"os"
+	"syscall"
+
+	"golang.org/x/sys/unix"
+)
+
+func copyFileWithSync(target, source string) error {
+	src, err := os.Open(source)
+	if err != nil {
+		return fmt.Errorf("failed to open source %s: %w", source, err)
+	}
+	defer src.Close()
+	tgt, err := os.Create(target)
+	if err != nil {
+		return fmt.Errorf("failed to open target %s: %w", target, err)
+	}
+	defer tgt.Close()
+	defer tgt.Sync()
+
+	info, err := src.Stat()
+	if err != nil {
+		return fmt.Errorf("failed to stat the source %s: %w", source, err)
+	}
+
+	srcSize := info.Size()
+	if err = tgt.Truncate(srcSize); err != nil {
+		return fmt.Errorf("failed to truncate the target %s: %w", target, err)
+	}
+
+	srcFd := int(src.Fd())
+	tgtFd := int(tgt.Fd())
+	offset := int64(0)
+	for offset < srcSize {
+		// search for the next hole segment
+		holeStart, err := unix.Seek(srcFd, offset, unix.SEEK_HOLE)
+		if err != nil {
+			if errno, ok := err.(syscall.Errno); ok && errno == syscall.ENXIO {
+				// no more holes found
+				// copy everything from the current offset till the end of the file
+				return doCopyFileRange(target, srcFd, tgtFd, &offset, int(srcSize-holeStart), 0)
+			}
+			return fmt.Errorf("failed to seek for holes in source %s: %w", source, err)
+		}
+
+		// this should never happen under normal conditions
+		// but better be safe than sorry, in case something goes VERY wrong
+		if holeStart < offset {
+			return fmt.Errorf("SEEK_HOLE returned a unexpected position, most likely due to an issue with the file (%s) or the filesystem themselves", source)
+		}
+
+		// a hole was found
+		if holeStart > offset {
+			// copy everything from the current offset till where the hole starts
+			if err := doCopyFileRange(target, srcFd, tgtFd, &offset, int(holeStart-offset), 0); err != nil {
+				return err
+			}
+		}
+
+		// search for the next data segment
+		dataStart, err := unix.Seek(srcFd, holeStart, unix.SEEK_DATA)
+		if err != nil {
+			if errno, ok := err.(syscall.Errno); ok && errno == syscall.ENXIO {
+				// no more data found, we reached the end of file for one of the two reasons:
+				// - we actually went through the whole file
+				// - the file's been created with `truncate -s ...` (or similar)
+				//   - meaning that there are no data segements at all
+				return nil
+			}
+			return fmt.Errorf("failed to seek for next data segment in source %s: %w", source, err)
+		}
+
+		// this should never happen under normal conditions
+		// but, again, better be safe than sorry, in case something goes VERY wrong
+		if dataStart == offset {
+			return fmt.Errorf("no progress happened in this copy iteration for the file %s, indicating a unexpected error", source)
+		}
+
+		// update the offset and do everything again till we reach the end of the file
+		offset = dataStart
+	}
+	return nil
+
+}
+
+func doCopyFileRange(target string, srcFd, tgtFd int, offset *int64, length int, flags uint) error {
+	for length > 0 {
+		copied, err := unix.CopyFileRange(srcFd, offset, tgtFd, offset, length, 0)
+		if err != nil || copied == 0 {
+			return fmt.Errorf("failed to copy file to target %s: %w", target, err)
+		}
+		length -= copied
+	}
+	return nil
+}