unix: Add comments about icons and external sockets

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

include/image.h

@@ -17,6 +17,19 @@
  */
 #define REMAP_GHOST	(1 << 31)
 
+/*
+ * By-default, when dumping a unix socket, we should dump its peer
+ * as well. Which in turn means, we should dump the task(s) that have
+ * this peer opened.
+ *
+ * Sometimes, we can break this rule and dump only one end of the
+ * unix sockets pair, and on restore time connect() this end back to
+ * its peer.
+ *
+ * So, to resolve this situation we mark the peers we don't dump
+ * as "external" and require the --ext-unix-sk option.
+ */
+
 #define USK_EXTERN	(1 << 0)
 
 #define VMA_AREA_NONE		(0 <<  0)

sk-unix.c

@@ -242,6 +242,12 @@ dump:
 	if (pb_write_one(fdset_fd(glob_fdset, CR_FD_UNIXSK), &ue, PB_UNIX_SK))
 		goto err;
 
+	/*
+	 * If a stream listening socket has non-zero rqueue, this
+	 * means there are in-flight connections waiting to get
+	 * accept()-ed. We handle them separately with the "icons"
+	 * (i stands for in-flight, cons -- for connections) things.
+	 */
 	if (sk->rqlen != 0 && !(sk->type == SOCK_STREAM &&
 				sk->state == TCP_LISTEN))
 		if (dump_sk_queue(lfd, ue.id))