diff --git a/sys/kern/subr_compressor.c b/sys/kern/subr_compressor.c
--- a/sys/kern/subr_compressor.c
+++ b/sys/kern/subr_compressor.c
@@ -538,6 +538,12 @@
 	return (s);
 }
 
+int
+compressor_format(const struct compressor *stream)
+{
+	return (stream->methods->format);
+}
+
 void
 compressor_reset(struct compressor *stream)
 {
diff --git a/sys/sys/compressor.h b/sys/sys/compressor.h
--- a/sys/sys/compressor.h
+++ b/sys/sys/compressor.h
@@ -42,6 +42,7 @@
 bool		compressor_avail(int format);
 struct compressor *compressor_init(compressor_cb_t cb, int format,
 		    size_t maxiosize, int level, void *arg);
+int		compressor_format(const struct compressor *stream);
 void		compressor_reset(struct compressor *stream);
 int		compressor_write(struct compressor *stream, void *data,
 		    size_t len);