unix/dgram: use minimal possible socket buffer for PF_UNIX/SOCK_DGRAM

This change fully splits away PF_UNIX/SOCK_DGRAM from other socket
buffer implementations, without any behavior changes.

Generic socket implementation is reduced down to one STAILQ and very
little code.

Reviewed by:		markj
Differential revision:	https://reviews.freebsd.org/D35300

1 files changed, 8 insertions, 0 deletions

diff --git a/sys/sys/sockbuf.h b/sys/sys/sockbuf.h
index 7800b2790c04..a1fd65d1a9e5 100644
--- a/sys/sys/sockbuf.h
+++ b/sys/sys/sockbuf.h
@@ -133,6 +133,14 @@ struct sockbuf {
 			uint64_t sb_tls_seqno;	/* TLS seqno */
 			struct	ktls_session *sb_tls_info; /* TLS state */
 		};
+		/*
+		 * PF_UNIX/SOCK_DGRAM
+		 *
+		 * Local protocol, thus any socket buffer is a receive buffer.
+		 */
+		struct {
+			STAILQ_HEAD(, mbuf)	uxdg_mb;
+		};
 	};
 };