Move mount to core/mount

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

core/mount/temp.go

@@ -0,0 +1,82 @@
+/*
+   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 mount
+
+import (
+	"context"
+	"fmt"
+	"os"
+
+	"github.com/containerd/log"
+)
+
+var tempMountLocation = getTempDir()
+
+// WithTempMount mounts the provided mounts to a temp dir, and pass the temp dir to f.
+// The mounts are valid during the call to the f.
+// Finally we will unmount and remove the temp dir regardless of the result of f.
+func WithTempMount(ctx context.Context, mounts []Mount, f func(root string) error) (err error) {
+	root, uerr := os.MkdirTemp(tempMountLocation, "containerd-mount")
+	if uerr != nil {
+		return fmt.Errorf("failed to create temp dir: %w", uerr)
+	}
+	// We use Remove here instead of RemoveAll.
+	// The RemoveAll will delete the temp dir and all children it contains.
+	// When the Unmount fails, RemoveAll will incorrectly delete data from
+	// the mounted dir. However, if we use Remove, even though we won't
+	// successfully delete the temp dir and it may leak, we won't loss data
+	// from the mounted dir.
+	// For details, please refer to #1868 #1785.
+	defer func() {
+		if uerr = os.Remove(root); uerr != nil {
+			log.G(ctx).WithError(uerr).WithField("dir", root).Error("failed to remove mount temp dir")
+		}
+	}()
+
+	// We should do defer first, if not we will not do Unmount when only a part of Mounts are failed.
+	defer func() {
+		if uerr = UnmountMounts(mounts, root, 0); uerr != nil {
+			uerr = fmt.Errorf("failed to unmount %s: %w", root, uerr)
+			if err == nil {
+				err = uerr
+			} else {
+				err = fmt.Errorf("%s: %w", uerr.Error(), err)
+			}
+		}
+	}()
+	if uerr = All(mounts, root); uerr != nil {
+		return fmt.Errorf("failed to mount %s: %w", root, uerr)
+	}
+	if err := f(root); err != nil {
+		return fmt.Errorf("mount callback failed on %s: %w", root, err)
+	}
+	return nil
+}
+
+// WithReadonlyTempMount mounts the provided mounts to a temp dir as readonly,
+// and pass the temp dir to f. The mounts are valid during the call to the f.
+// Finally we will unmount and remove the temp dir regardless of the result of f.
+func WithReadonlyTempMount(ctx context.Context, mounts []Mount, f func(root string) error) (err error) {
+	return WithTempMount(ctx, readonlyMounts(mounts), f)
+}
+
+func getTempDir() string {
+	if xdg := os.Getenv("XDG_RUNTIME_DIR"); xdg != "" {
+		return xdg
+	}
+	return os.TempDir()
+}