layers: continue on non-existing volume in dep-scan

When checking for an unused volume, we need to expand all available
volumes. However, in case another deletion process is happening at
the same time, there can be volumes we can list, but no longer
check for dependencies. This would lead to errors during deletion,
even though all volumes are in the expected layout.

As a workaround (a fix would require syncronising volume creation/deletion
between virter invocations): Ignore errors generated because a volume
does no longer exist during checking if a volume is unused.

Author: WanzenBug

internal/virter/layer.go

@@ -11,6 +11,7 @@ import (
 	"compress/gzip"
 	"crypto/sha256"
 	"encoding/hex"
+	"errors"
 	"fmt"
 	"hash"
 	"io"
@@ -503,6 +504,13 @@ func (rl *RawLayer) DeleteIfUnused() (bool, error) {
 		if err != nil {
 			_, isNonVirter := err.(*nonVirterVolumeError)
 			if isNonVirter {
+				// Not a virter format volume -> shouldn't depend on our volumes.
+				continue
+			}
+
+			e := libvirt.Error{}
+			if errors.As(err, &e) && e.Code == uint32(errNoStorageVol) {
+				// Volume already deleted -> can't have a relevant dependency anyways.
 				continue
 			}