storagenode/blobstore: minor simplifications

In one case, we don't need to do an extra stat() call at the top of the
function every time we trash a blob, since we os.MkdirAll() a descendant
of that same directory a little bit further down. Any os.IsNotExist
errors coming from the rename call are definitely talking about the
source file, not the destination directory (unless of course the dest
directory was deleted somehow concurrently, but that problem already
existed so we're not making it worse).

In the second case, we don't necessarily need special code to handle the
possibility of a v0PieceAccess, because this is the blob store layer,
which doesn't know anything about pieces. All blobs are blobs, to the
blob store. (Even if that weren't the case, we only put FormatV1 blobs
into the trash, so it still couldn't be a v0PieceAccess.) Add some extra
info to diagnose the situation better if it ever happens.

Change-Id: Idc2c2f79dbd2f6b9e4fdb28da19d0241d4596d47

storagenode/blobstore/filestore/dir.go

@@ -323,13 +323,6 @@ func (dir *Dir) Trash(ctx context.Context, ref blobstore.BlobRef) (err error) {
 
 // TrashWithStorageFormat moves the blob specified by ref to the trash for the specified format version.
 func (dir *Dir) TrashWithStorageFormat(ctx context.Context, ref blobstore.BlobRef, formatVer blobstore.FormatVersion) (err error) {
-	// Ensure trashdir exists so that we know any os.IsNotExist errors below
-	// are not from a missing trash dir
-	_, err = os.Stat(dir.trashdir())
-	if err != nil {
-		return err
-	}
-
 	blobsBasePath, err := dir.blobToBasePath(ref)
 	if err != nil {
 		return err
@@ -475,12 +468,11 @@ func (dir *Dir) EmptyTrash(ctx context.Context, namespace []byte, trashedBefore
 			if errors.Is(err, ErrIsDir) {
 				return nil
 			}
-			// it would be best if we could report the actual problematic path
 			if thisBlobInfo, ok := info.(*blobInfo); ok {
-				errorsEncountered.Add(Error.New("%s: %s", thisBlobInfo.path, err))
+				errorsEncountered.Add(Error.New("%s: %w", thisBlobInfo.path, err))
 			} else {
-				// this is probably a v0PieceAccess; do what we can
-				errorsEncountered.Add(Error.New("blobRef %+v: %s", info.BlobRef(), err))
+				// if this happens, it's time to extend the code to handle the other type
+				errorsEncountered.Add(Error.New("%+v [unexpected type %T]: %w", info, info, err))
 			}
 			return nil
 		}