Use default writable size in erofs snapshotter for non-Linux hosts

dmcgowan · k8s-infra-cherrypick-robot · commit 9da97686d151 · 2025-11-19T00:13:56.000Z
Non-Linux hosts are not expected to be able to directly mount erofs
snapshotters on the host system. Non-Linux hosts should use block mode
by default with a reasonably set default block size.

Signed-off-by: Derek McGowan &lt;derek@mcg.dev&gt;
diff --git a/plugins/snapshots/erofs/erofs.go b/plugins/snapshots/erofs/erofs.go
@@ -95,7 +95,9 @@ type snapshotter struct {
 // NewSnapshotter returns a Snapshotter which uses EROFS+OverlayFS. The layers
 // are stored under the provided root. A metadata file is stored under the root.
 func NewSnapshotter(root string, opts ...Opt) (snapshots.Snapshotter, error) {
-	var config SnapshotterConfig
+	config := SnapshotterConfig{
+		defaultSize: defaultWritableSize,
+	}
 	for _, opt := range opts {
 		opt(&config)
 	}
@@ -104,8 +106,11 @@ func NewSnapshotter(root string, opts ...Opt) (snapshots.Snapshotter, error) {
 		return nil, err
 	}
 
-	if err := checkCompatibility(root); err != nil {
-		return nil, err
+	if config.defaultSize == 0 {
+		// If not block mode, check root compatibility
+		if err := checkCompatibility(root); err != nil {
+			return nil, err
+		}
 	}
 
 	// Check fsverity support if enabled
diff --git a/plugins/snapshots/erofs/erofs_linux.go b/plugins/snapshots/erofs/erofs_linux.go
@@ -33,6 +33,10 @@ import (
 	"github.com/containerd/containerd/v2/internal/erofsutils"
 )
 
+// defaultWritableSize is set to 0 for Linux to match the default behavior of
+// other snapshotters available on Linux.
+const defaultWritableSize = 0
+
 // check if EROFS kernel filesystem is registered or not
 func findErofs() bool {
 	fs, err := os.ReadFile("/proc/filesystems")
diff --git a/plugins/snapshots/erofs/erofs_other.go b/plugins/snapshots/erofs/erofs_other.go
@@ -24,6 +24,11 @@ import (
 	"github.com/containerd/errdefs"
 )
 
+// defaultWritableSize is the default size allocation for writable
+// layers on non-Linux platforms. This is set to 64MiB but may be
+// adjusted in the user configuration or per snapshot.
+const defaultWritableSize = 64 * 1024 * 1024
+
 func checkCompatibility(root string) error {
 	return nil
 }

Original file line number	Diff line number	Diff line change
`@@ -24,6 +24,11 @@ import (`
`24`	`24`	`"github.com/containerd/errdefs"`
`25`	`25`	`)`
`26`	`26`
	`27`	`+// defaultWritableSize is the default size allocation for writable`
	`28`	`+// layers on non-Linux platforms. This is set to 64MiB but may be`
	`29`	`+// adjusted in the user configuration or per snapshot.`
	`30`	`+const defaultWritableSize = 64 * 1024 * 1024`
	`31`	`+`
`27`	`32`	`func checkCompatibility(root string) error {`
`28`	`33`	`return nil`
`29`	`34`	`}`