Update fsview to allow type registration

Move erofs implementation to plugin and register with fsview.

Signed-off-by: Derek McGowan <derek@mcg.dev>

plugins/mount/fsview/erofs/erofs.go

@@ -0,0 +1,125 @@
+/*
+   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 erofs
+
+import (
+	"errors"
+	"io"
+	"io/fs"
+	"os"
+	"strings"
+
+	"github.com/containerd/containerd/v2/core/mount"
+	"github.com/containerd/containerd/v2/internal/fsview"
+	"github.com/containerd/errdefs"
+	"github.com/erofs/go-erofs"
+)
+
+func init() {
+	fsview.Register(fsview.FSHandler{
+		HandleMount: handleMount,
+		Getxattr:    getxattr,
+		IsWhiteout:  isWhiteout,
+	})
+}
+
+func handleMount(m mount.Mount) (fsview.View, error) {
+	if m.Type != "erofs" {
+		return nil, errdefs.ErrNotImplemented
+	}
+
+	f, err := os.Open(m.Source)
+	if err != nil {
+		return nil, err
+	}
+
+	var extraDevices []io.ReaderAt
+	var closers []io.Closer
+	closers = append(closers, f)
+
+	for _, opt := range m.Options {
+		if devPath, ok := strings.CutPrefix(opt, "device="); ok {
+			if devPath == "" {
+				continue
+			}
+			df, err := os.Open(devPath)
+			if err != nil {
+				for _, c := range closers {
+					c.Close()
+				}
+				return nil, err
+			}
+			closers = append(closers, df)
+			extraDevices = append(extraDevices, df)
+		}
+	}
+
+	var opts []erofs.OpenOpt
+	if len(extraDevices) > 0 {
+		opts = append(opts, erofs.WithExtraDevices(extraDevices...))
+	}
+
+	efs, err := erofs.Open(f, opts...)
+	if err != nil {
+		for _, c := range closers {
+			c.Close()
+		}
+		return nil, err
+	}
+
+	return &erofsView{
+		FS:      efs,
+		closers: closers,
+	}, nil
+}
+
+type erofsView struct {
+	fs.FS
+	closers []io.Closer
+}
+
+func (v *erofsView) Close() error {
+	var errs []error
+	for _, c := range v.closers {
+		errs = append(errs, c.Close())
+	}
+	return errors.Join(errs...)
+}
+
+func getxattr(f fs.File, name string) (string, bool) {
+	fi, err := f.Stat()
+	if err != nil {
+		return "", false
+	}
+	estatfi, ok := fi.Sys().(*erofs.Stat)
+	if !ok {
+		return "", false
+	}
+	val, ok := estatfi.Xattrs[name]
+	return val, ok
+}
+
+func isWhiteout(fi fs.FileInfo) bool {
+	if (fi.Mode() & fs.ModeCharDevice) == 0 {
+		return false
+	}
+	estatfi, ok := fi.Sys().(*erofs.Stat)
+	if !ok {
+		return false
+	}
+	return estatfi.Rdev == 0
+}